EinTopaz Posted March 15 Posted March 15 (edited) Hey all, Investigating some ongoing weirdness with the CH on the ground floor and looking for some insight. On the ground floor we have a Worcester Bosch Greenstar life 8000 System boiler (35kw variant). It powers 15 radiators on the ground floor which are a mix of large type 22 double panels, and some triple column designer types too. Total wattage of those at T50 is around 29kw total, ish. Also worth mentioning this boiler does not power any hot water in the property, that's dealt with elsewhere. This boiler is CH only. I'm getting three annoying symptoms that I can't seem to eliminate no matter how many times I balance and bleed etc. They are:- When I turn on the boiler the LCD for flow temp goes up real quick though the radiators take a long time to get heat in them. Eventually the boiler ends up getting to 70degrees or so, then modulating itself down to 50% or so before some of the radiators are anything more than warm. Im seeing an inconsistency where sometimes some radiators will be fine temperature wise, and other times they wont get hot. I.e radiator 5 was piping hot when I ran the heating last time, this time it's cooler than some of the others (with no balancing between the tests). I seem to need to let air out of the towel radiator in the bathroom every couple weeks or so. (this is the radiator in the circuit that has no TRV). Could the above be caused by an insufficiently sized Expansion vessel? Or would it suggest something else? Thoughts and insights greatly appreciated. thanks! Ged Edited March 15 by EinTopaz
EinTopaz Posted March 18 Author Posted March 18 Bumping this - anyone on here knowledgeable of the above? 🙂
JohnMo Posted March 18 Posted March 18 How old is the system? Was it ok in the past? Are you also having to top up water in the system? Have you checked the expansion vessel for charge pressure? On 15/03/2025 at 14:22, EinTopaz said: Could the above be caused by an insufficiently sized Expansion vessel Expand I doubt it, the expansion vessel is there to stop the system exploding by giving an expansion route.
EinTopaz Posted March 18 Author Posted March 18 On 18/03/2025 at 21:46, JohnMo said: How old is the system? Was it ok in the past? Are you also having to top up water in the system? Have you checked the expansion vessel for charge pressure? I doubt it, the expansion vessel is there to stop the system exploding by giving an expansion route. Expand Always had the symptoms though i originally thought some of it was due to poor balance, but its been balanced over and over and over, still the same inconsistencies. 12 months old system, brand new boiler, all pipework, all rads. All went in at the same time. Have not checked the chare pressure yet as its a system boiler with everything inside. Wasn't really sure how to check it in this type of setup. I did check the manual for what they recommend and saw this graph however.... i plotted the red X on where we are. I calculated we're at 150L or so based on all the specs of my radiators. (the designer triple column ones take up so much water!) I can't see the size of the vessel inside referenced in the manual,. but looking on ebay for replacement parts, it would suggest the one i have inside is a 10L one.
marshian Posted March 18 Posted March 18 On 15/03/2025 at 14:22, EinTopaz said: Hey all, Investigating some ongoing weirdness with the CH on the ground floor and looking for some insight. On the ground floor we have a Worcester Bosch Greenstar life 8000 System boiler (35kw variant). It powers 15 radiators on the ground floor which are a mix of large type 22 double panels, and some triple column designer types too. Total wattage of those at T50 is around 29kw total, ish. Also worth mentioning this boiler does not power any hot water in the property, that's dealt with elsewhere. This boiler is CH only. I'm getting three annoying symptoms that I can't seem to eliminate no matter how many times I balance and bleed etc. They are:- When I turn on the boiler the LCD for flow temp goes up real quick though the radiators take a long time to get heat in them. Eventually the boiler ends up getting to 70degrees or so, then modulating itself down to 50% or so before some of the radiators are anything more than warm. Im seeing an inconsistency where sometimes some radiators will be fine temperature wise, and other times they wont get hot. I.e radiator 5 was piping hot when I ran the heating last time, this time it's cooler than some of the others (with no balancing between the tests). I seem to need to let air out of the towel radiator in the bathroom every couple weeks or so. (this is the radiator in the circuit that has no TRV). Could the above be caused by an insufficiently sized Expansion vessel? Or would it suggest something else? Thoughts and insights greatly appreciated. thanks! Ged Expand Lot to go at there............. For a boiler to get to 70 deg flow really quickly yet the rads don't get there as fast is a bit odd - have you got an ABV in circuit that is allowing too much flow back to the boiler?? Why are you running the CH circuit at 70 deg C - that's way too high to get condensing benefit Whats the return temp coming back to the boiler? Could you list out Room / Rad Type / Size / Comment By comment I mean if it's a rad affected or one that seems to be fine all the time Vertical Rads are a whole different ball game if they don't have diverters in them If you can borrow a thermal camera it might give you some good clues on the flow internally thro the rad Below is one of my K22 or K33 rads running on a flow temp of ~30 Deg C And here is one of my vertical rads (with the modification internally) Below is a link to the issues I had with 2 vertical rads that were fitted with a diverter 1
Temp Posted March 19 Posted March 19 How old is the system? When you say it's always done it do you mean since built it or since you bought the house? My first thought is the system has a slot of sludge in it. Possibly no or not enough corrosion inhibitor? This could explain both the "air" and inconsistent flow. If that's a possibility I'd look at draining and refilling the system, turning it on to stir it up and repeat until the water is reasonably clear. Then dose it with the right amount of Fernox F1 or similar. Read the instructions. It's likely to need several bottles. Helps if you can measure the volume of water when you drained out earlier. Putting too much inhibitor in doesn't usually hurt. You can also get test kits to check the concentration. Other possibilities could be an intermittent of failing pump? Undersize or faulty expansion vessel normally caused water out of the PRV. 1
Nickfromwales Posted March 19 Posted March 19 Undersized capacity for expansion is number one issue here, and what happens is the system expands, a bit of loss from PRV to atmosphere, then the system cools down and creates a vacuum. That results in air being sucked in through the automatic air vents, and then repeat. You need to add another 14-18L of expansion vessel capacity before further diagnosing, as that may resolve more than one symptom here. If there’s insufficient inhibitor install is 12 months old then you need to get the original fitter back to do this FOC as they should have calculated the system volume and installed this from day 1; this may have now provoked the PRV to dribble even when back to normal duty so you’ll have to monitor this for discharge after the second expansion vessel is installed. Common to see tbh, as most don’t ever read the book word for word as they’re just wanting to be in and out asap on price. I think it’s a mix of gas and air that’s accumulating in the radiator that you’re routinely bleeding, and if there’s insufficient inhibitor then the corrosion process releases nitrogen (iirc) which gets released by a) the auto vents and b), you manually bleeding the rads. The issue of the boiler achieving such high temps so quickly points at pump flow rates being too low. One other possibility is that the pump isolation valves may have been inadvertently left part open instead of fully open (took me and 2 of my mates half a day of head scratching, to find this faux pas, where we had the same issues on a brand new job !!). How we laughed…… 1
marshian Posted March 19 Posted March 19 On 19/03/2025 at 11:19, Temp said: How old is the system? When you say it's always done it do you mean since built it or since you bought the house? Expand From a post from @EinTopaz above On 18/03/2025 at 21:54, EinTopaz said: 12 months old system, brand new boiler, all pipework, all rads. All went in at the same time. Expand
marshian Posted March 19 Posted March 19 On 19/03/2025 at 12:40, Nickfromwales said: The issue of the boiler achieving such high temps so quickly points at pump flow rates being too low. One other possibility is that the pump isolation valves may have been inadvertently left part open instead of fully open (took me and 2 of my mates half a day of head scratching, to find this faux pas, where we had the same issues on a brand new job !!). How we laughed…… Expand Oh I'd have laughed about that one too (in sympathy * rather than at you) * Note - I left a valve on a "magnaclean assembly" not fully open once - Boiler didn't like that at all - luckily it was the previous boiler cos it didn't half kettle when it tried to run!!! 1
EinTopaz Posted March 19 Author Posted March 19 On 18/03/2025 at 23:40, marshian said: Lot to go at there............. For a boiler to get to 70 deg flow really quickly yet the rads don't get there as fast is a bit odd - have you got an ABV in circuit that is allowing too much flow back to the boiler?? Why are you running the CH circuit at 70 deg C - that's way too high to get condensing benefit Whats the return temp coming back to the boiler? Could you list out Room / Rad Type / Size / Comment By comment I mean if it's a rad affected or one that seems to be fine all the time Vertical Rads are a whole different ball game if they don't have diverters in them If you can borrow a thermal camera it might give you some good clues on the flow internally thro the rad Below is one of my K22 or K33 rads running on a flow temp of ~30 Deg C And here is one of my vertical rads (with the modification internally) Below is a link to the issues I had with 2 vertical rads that were fitted with a diverter Expand As far as I know there's no ABV. I cannot see one externally anyway. There is solely one radiator in the circuit (towel rad in bathroom) that has no TRV Running 73 degrees because thats how hot i like the radiators. It does modulate down to 44% eventually after maybe an hour or so. and I can see fluid coming out of the condense pipe. So it is condensing. return temp, not sure. i'll list the rads out properly in a future post. good shout. also good shout on the vertical rads, i do have a FLIR camera so i'll take a look. Out of interest should they or should they not have diverters in there? the place i bought them off told me the TRV should be diagonally opposite the bleed valve because of something. I imagine that's related to what you're saying?
marshian Posted March 19 Posted March 19 On 19/03/2025 at 13:58, EinTopaz said: As far as I know there's no ABV. I cannot see one externally anyway. There is solely one radiator in the circuit (towel rad in bathroom) that has no TRV Expand OK so the next logical step is to see what the valves on each end of the bypass rad are doing - if one end has a knob on it and the other a cap cover remove the cap cover count the turns to fully closed Count the turns from closed to fully open Post up the results - it could be that this rad is allowing too much flow back to the boiler effectively slowing down house/rads warm up On 19/03/2025 at 13:58, EinTopaz said: Running 73 degrees because thats how hot i like the radiators. It does modulate down to 44% eventually after maybe an hour or so. and I can see fluid coming out of the condense pipe. So it is condensing. Expand I get the personal preference element but if the circuit is running at that temp unless the house is absolutely massive and has a horrendous heat loss when it's up to temp the boiler is going to cycle a lot 44% of 35kW is 15.4 kWh - that is pretty heavy usage!!! On 19/03/2025 at 13:58, EinTopaz said: return temp, not sure. Expand Sometimes you can view it in the boiler parmeters menu Below 54 deg is essential for condensing 73 deg flow some boilers get upset if the return flow is greater than 20 -25 deg C so I'd guess your return once house is up to temp would be between 48 and 53 Deg C so only just scraping into condensing mode so running at maybe 90% efficiency as opposed to a 55 deg flow and a 35 Deg Return returning 96% Efficiency On 19/03/2025 at 13:58, EinTopaz said: i'll list the rads out properly in a future post. good shout. Expand Please do On 19/03/2025 at 13:58, EinTopaz said: also good shout on the vertical rads, i do have a FLIR camera so i'll take a look. Expand If you already have a FLIR camera then the images will tell you a lot about where the heat and the flow is moving round I never took a picture of my verticals that had a problem but the bottom rail of the rad was hot and the vertical bars were stone cold!!!! On 19/03/2025 at 13:58, EinTopaz said: Out of interest should they or should they not have diverters in there? the place i bought them off told me the TRV should be diagonally opposite the bleed valve because of something. I imagine that's related to what you're saying? Expand Modern TRV's that are bi-directional don't care which end they are on Vertical rads should have diverters in there to help them work in lower flow temp systems Good manufacturers clearly mark up the position of the diverter, the in and out One of the pages of instructions with my big double vertical is below as you can hopefully see the instruction are very specific 1
John Carroll Posted March 19 Posted March 19 On 18/03/2025 at 21:54, EinTopaz said: Always had the symptoms though i originally thought some of it was due to poor balance, but its been balanced over and over and over, still the same inconsistencies. 12 months old system, brand new boiler, all pipework, all rads. All went in at the same time. Have not checked the chare pressure yet as its a system boiler with everything inside. Wasn't really sure how to check it in this type of setup. I did check the manual for what they recommend and saw this graph however.... i plotted the red X on where we are. I calculated we're at 150L or so based on all the specs of my radiators. (the designer triple column ones take up so much water!) I can't see the size of the vessel inside referenced in the manual,. but looking on ebay for replacement parts, it would suggest the one i have inside is a 10L one. Expand The above gives different precharge pressures but no charging pressures which makes a big difference to the system volumes that can be accomodated by a (the) 10L EV. For example they indicate that at a system mean temp of 65C that the EV wiil be sufficient for 180/185L, it will, (my calcs) but just about with precharge/filling pressures of 0.75/1.25bar, I would allways calculate for a final pressure of 2.5bar so the 10L EV will comfortably accomodate 150L with precharge/filling pressures of 0.75bar/1.25bar with a final pressure of 2.5bar. Commonly used precharge/filling pressures of 1.0bar/1.5bar should give a final pressure of 3.0bar with a system vol of 163L but only 125L at a final pressure of 2.5bar. A "trick" thats sometimes used is to have the precharge and filling pressures the same which gives a huge increase in system volume, for example the 125L above at precharge/filling pressures of 1.0/1.5bar can be increased to over 230L with precharge/filling pressures of 1.0bar/1.0bar and still not exceed a final pressure of 2.5bar, of course no reserve vol then to make up for tiny leakages/microbubbles which can lead to frequent top ups, or, far worse, the installation of a auto top up (PRV) valve set to 1.0bar. EV Rev 0.xlsxFetching info... 1
Temp Posted March 19 Posted March 19 On 15/03/2025 at 14:22, EinTopaz said: When I turn on the boiler the LCD for flow temp goes up real quick though the radiators take a long time to get heat in them. Eventually the boiler ends up getting to 70degrees or so, then modulating itself down to 50% or so before some of the radiators are anything more than warm. Expand When it starts modulating down prematurely what actually happens to the the flow and return temperature? Think the return temperature should give clues. 1
EinTopaz Posted March 21 Author Posted March 21 (edited) On 19/03/2025 at 15:07, marshian said: OK so the next logical step is to see what the valves on each end of the bypass rad are doing - if one end has a knob on it and the other a cap cover remove the cap cover count the turns to fully closed Count the turns from closed to fully open Post up the results - it could be that this rad is allowing too much flow back to the boiler effectively slowing down house/rads warm up I get the personal preference element but if the circuit is running at that temp unless the house is absolutely massive and has a horrendous heat loss when it's up to temp the boiler is going to cycle a lot 44% of 35kW is 15.4 kWh - that is pretty heavy usage!!! Sometimes you can view it in the boiler parmeters menu Below 54 deg is essential for condensing 73 deg flow some boilers get upset if the return flow is greater than 20 -25 deg C so I'd guess your return once house is up to temp would be between 48 and 53 Deg C so only just scraping into condensing mode so running at maybe 90% efficiency as opposed to a 55 deg flow and a 35 Deg Return returning 96% Efficiency Please do If you already have a FLIR camera then the images will tell you a lot about where the heat and the flow is moving round I never took a picture of my verticals that had a problem but the bottom rail of the rad was hot and the vertical bars were stone cold!!!! Modern TRV's that are bi-directional don't care which end they are on Vertical rads should have diverters in there to help them work in lower flow temp systems Good manufacturers clearly mark up the position of the diverter, the in and out One of the pages of instructions with my big double vertical is below as you can hopefully see the instruction are very specific Expand Yeah nice, thankyou for this. I will put the thermal cam on this weekend and see what's going on. The designer radiators are called "Milano Windsor" from Bestheating.com I called their "technical support team" and asked about whether they have a diverter already in etc, they said they're required because these rads are specifically designed for water to go not simply pass through the bottom. So sounds like they have an internal baffle of some sort already, they also said it doesn't matter which way they're fitted, front to back, upside down. They said the design is symmetrical in box axis.... That said I've not put the thermal cam on yet. Appreciate your point about heating temp, it is a large property, hence why we put this second boiler on the ground floor solely to do rads. Tbh most rooms do get nicely to temp, just the inconsistency of which rads get hot and the boiler modulating down prematurely are the two things giving me a headache. The rad without the TRV is actually a towel radiator. Like the one below. Which do I adjust to essentially dial the bypassing down? Edited March 21 by EinTopaz
EinTopaz Posted March 21 Author Posted March 21 On 19/03/2025 at 17:13, Temp said: When it starts modulating down prematurely what actually happens to the the flow and return temperature? Think the return temperature should give clues. Expand Return temp i've got no idea, it doesn't let you see that on the LCD display.I need to monitor it myself with one of those fish tank thermometer things. On the flow temp, it does one of two things. Either hits target temp, of 73' or so, then goes entirely off (burner goes off) for maybe 30-60seconds? during that time the flow temp drops by about 25-30 degrees. Then modulates down to a lower % and gradually creeps back up to 73' then stays there stably. Sometimes it just gets to temp and modulates down incrementally. But either way its showing a higher number there than what i'm "feeling" on the rads for the first hour. Though interestingly when i whack it into "chimney sweep mode" everything gets dead hot.
EinTopaz Posted March 21 Author Posted March 21 On 19/03/2025 at 15:25, John Carroll said: The above gives different precharge pressures but no charging pressures which makes a big difference to the system volumes that can be accomodated by a (the) 10L EV. For example they indicate that at a system mean temp of 65C that the EV wiil be sufficient for 180/185L, it will, (my calcs) but just about with precharge/filling pressures of 0.75/1.25bar, I would allways calculate for a final pressure of 2.5bar so the 10L EV will comfortably accomodate 150L with precharge/filling pressures of 0.75bar/1.25bar with a final pressure of 2.5bar. Commonly used precharge/filling pressures of 1.0bar/1.5bar should give a final pressure of 3.0bar with a system vol of 163L but only 125L at a final pressure of 2.5bar. A "trick" thats sometimes used is to have the precharge and filling pressures the same which gives a huge increase in system volume, for example the 125L above at precharge/filling pressures of 1.0/1.5bar can be increased to over 230L with precharge/filling pressures of 1.0bar/1.0bar and still not exceed a final pressure of 2.5bar, of course no reserve vol then to make up for tiny leakages/microbubbles which can lead to frequent top ups, or, far worse, the installation of a auto top up (PRV) valve set to 1.0bar. EV Rev 0.xlsx 11.72 kB · 2 downloads Expand thanks, the graph i posted above does allude to the fact it might be fine if I run a really low charge pressure. But based on the fact that I guess there's no such thing as too much expansion capacity. I may as well just add another 18L rather than fiddling about with the internals of the boiler.
John Carroll Posted March 21 Posted March 21 (edited) You might also consider getting this service valve installed as it means the system does not require draining to check the EV precharge pressure at the normal boiler service intervals. Edited March 21 by John Carroll 1
marshian Posted March 21 Posted March 21 On 21/03/2025 at 13:38, EinTopaz said: Yeah nice, thankyou for this. I will put the thermal cam on this weekend and see what's going on. Expand Yeah regardless of the flow temp they show whats going on flow wise inside a rad On 21/03/2025 at 13:38, EinTopaz said: The designer radiators are called "Milano Windsor" from Bestheating.com I called their "technical support team" and asked about whether they have a diverter already in etc, they said they're required because these rads are specifically designed for water to go not simply pass through the bottom. So sounds like they have an internal baffle of some sort already, they also said it doesn't matter which way they're fitted, front to back, upside down. They said the design is symmetrical in box axis.... That said I've not put the thermal cam on yet. Expand Good news that they are fitted - hopefully they are better quality than two I bought from a different manufacturer On 21/03/2025 at 13:38, EinTopaz said: Appreciate your point about heating temp, it is a large property, hence why we put this second boiler on the ground floor solely to do rads. Tbh most rooms do get nicely to temp, just the inconsistency of which rads get hot and the boiler modulating down prematurely are the two things giving me a headache. Expand I'm still surprised that you need that high a flow temp unless you are heating to a schedule (ie morning on - daytime off and evening on) I'll cover the boiler issue in a separate reply On 21/03/2025 at 13:38, EinTopaz said: The rad without the TRV is actually a towel radiator. Like the one below. Which do I adjust to essentially dial the bypassing down? Expand You can do either (or both equally because towel rails are a PITA) I'd feel the pipes to see which one gets hot first and throttle that one back
marshian Posted March 21 Posted March 21 On 21/03/2025 at 13:42, EinTopaz said: Return temp i've got no idea, it doesn't let you see that on the LCD display.I need to monitor it myself with one of those fish tank thermometer things. Expand Or even your thermal camera wil give you a half decent answer 😉 On 21/03/2025 at 13:42, EinTopaz said: On the flow temp, it does one of two things. Either hits target temp, of 73' or so, then goes entirely off (burner goes off) for maybe 30-60seconds? during that time the flow temp drops by about 25-30 degrees. Then modulates down to a lower % and gradually creeps back up to 73' then stays there stably. Expand Ahh I'm so familar with this symptom - it's very common on Glow-worm or Valiant - I reckon the boiler is not liking the delta (difference between flow and return) it's seeing being way above 20 deg C Example Cold start lets say circuit temp is 20 deg C (Rads same temps as rooms) - Boiler fires up and gives the circuit 75-85 of max output and boiler set point is 73 Deg so hits that temp. It's a big circuit will a lot of rads - return doesn't rise very quickly and the boiler is seeing 20 deg still - Delta is 53 Deg C As a result the boiler either shuts down or throttles back to min modulation - flow temp drops down to 40's and the boiler waits to put more energy into the circuit when the return temps start to rise before adding more heat again Several ways to delay with this - one is drop the target flow temp so the delta isn't so big but you clearly don't want to do that On 21/03/2025 at 13:42, EinTopaz said: Sometimes it just gets to temp and modulates down incrementally. But either way its showing a higher number there than what i'm "feeling" on the rads for the first hour. Expand Boiler isn't happy - may even be the case that the flow temp displayed isn't the flow temp being sent out of the boiler On 21/03/2025 at 13:42, EinTopaz said: Though interestingly when i whack it into "chimney sweep mode" everything gets dead hot. Expand I'm not a gas engineer (just an enthusiast that quite likes the mechanics of house heating systems and I quite like reading boiler manuals) but I really don't think that is a very good idea and you could potentially damage the heat exchanger as a result of the thermal shock or the large temp differential.
John Carroll Posted March 21 Posted March 21 On 15/03/2025 at 14:22, EinTopaz said: Hey all, Investigating some ongoing weirdness with the CH on the ground floor and looking for some insight. On the ground floor we have a Worcester Bosch Greenstar life 8000 System boiler (35kw variant). It powers 15 radiators on the ground floor which are a mix of large type 22 double panels, and some triple column designer types too. Total wattage of those at T50 is around 29kw total, ish. Also worth mentioning this boiler does not power any hot water in the property, that's dealt with elsewhere. This boiler is CH only. I'm getting three annoying symptoms that I can't seem to eliminate no matter how many times I balance and bleed etc. They are:- When I turn on the boiler the LCD for flow temp goes up real quick though the radiators take a long time to get heat in them. Eventually the boiler ends up getting to 70degrees or so, then modulating itself down to 50% or so before some of the radiators are anything more than warm. Im seeing an inconsistency where sometimes some radiators will be fine temperature wise, and other times they wont get hot. I.e radiator 5 was piping hot when I ran the heating last time, this time it's cooler than some of the others (with no balancing between the tests). I seem to need to let air out of the towel radiator in the bathroom every couple weeks or so. (this is the radiator in the circuit that has no TRV). Could the above be caused by an insufficiently sized Expansion vessel? Or would it suggest something else? Thoughts and insights greatly appreciated. thanks! Ged Expand Get someone to check the circ pump settings, possibly require setting 5 or 6 to give a residual head of 3.5 to 4.0M .
EinTopaz Posted March 22 Author Posted March 22 On 21/03/2025 at 22:52, John Carroll said: Get someone to check the circ pump settings, possibly require setting 5 or 6 to give a residual head of 3.5 to 4.0M . Expand Yep this was my first plan of attack funnily enough, as i suspected it perhaps wasn't getting the heat away from the boiler quickly enough. Ive been running it at 6 for the past few weeks, no discernable difference really. There is another pump mode you can put the pump in where it's speed is relative to the burner output. In the manual that reads as if the max in that mode is far higher than 400mbar....but when I tried that mode i got some very bizarre results, even worse than constant pressure.
EinTopaz Posted March 22 Author Posted March 22 On 21/03/2025 at 16:12, John Carroll said: You might also consider getting this service valve installed as it means the system does not require draining to check the EV precharge pressure at the normal boiler service intervals. Expand will that work with a system boiler where the expansion is internal?
EinTopaz Posted March 22 Author Posted March 22 On 18/03/2025 at 23:40, marshian said: Lot to go at there............. For a boiler to get to 70 deg flow really quickly yet the rads don't get there as fast is a bit odd - have you got an ABV in circuit that is allowing too much flow back to the boiler?? Why are you running the CH circuit at 70 deg C - that's way too high to get condensing benefit Whats the return temp coming back to the boiler? Could you list out Room / Rad Type / Size / Comment By comment I mean if it's a rad affected or one that seems to be fine all the time Vertical Rads are a whole different ball game if they don't have diverters in them If you can borrow a thermal camera it might give you some good clues on the flow internally thro the rad Below is one of my K22 or K33 rads running on a flow temp of ~30 Deg C And here is one of my vertical rads (with the modification internally) Below is a link to the issues I had with 2 vertical rads that were fitted with a diverter Expand No issue with the designer rads in and of themselves, as far as I can see.
marshian Posted March 22 Posted March 22 On 22/03/2025 at 10:16, EinTopaz said: No issue with the designer rads in and of themselves, as far as I can see. Expand Not showing much of a temp gradient either.............. Not exactly what I would expect to see but they are heating up evenly and a vertical rad will do that at high temps even if there is no baffle/diverter - the hot water wants to rise above the cold so you'll get a very similar picture. It's exactly the problem I had with a couple of verticals - at 55 deg flow temps they heated up nicely but as I dropped the flow temps to 40 deg it became really clear that there was an issue with the baffle as the heat differential wasn't big enough and the flow to fast for the hotter water to have time to rise. Can you run the boiler at a lower flow temp and do the pictures again - maybe down at 40 deg - that should provide a better picture Now I know I'm using low flow temps to heat my house (32 deg C max) but the above is a large vertical and shows clearly the impact of the diverter. At this time of year your heat losses should be much lower so 73 deg flow temp is just going to drive room overheat or if TRV controlled rooms a circuit shrinking and boiler cycling (all of which is bad for energy consumption) 1
marshian Posted March 22 Posted March 22 Just to add before I had WC control of flow temps I was manually adjusting flow temps on the boiler - roughly in line with Autumn 45 - 50 Deg C Winter 50 - 60 Deg C (really cold days I'd have to bump it up to 65 Deg C) Spring 45 - 50 Deg C My old boiler min flow temp was 39 deg C but practically it was effectively 45 deg C as a lowest flow temp Occasional colder days in the shoulder seasons where I needed to put a bit of heat in the house I'd just boost the heating for an hour at 50 deg Despite insulation improvements parts of my house do need heating unless outside temps are consistently above 16.5 deg C South facing side is normally fine - sunshine on that side means living room, Dining room and two bedrooms will soak up some solar gain and need minimal contribution from CH circuit during daytime North side is not so good and temps in study, bedroom, kitchen, toilet, utility, front hall, both bathrooms and the hallway, stairs and landing all can be 4 to 5 deg lower in daylight hours. 1
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