marshian

Target temp of 65 is pretty high if you have decently sized rads - I'm unsure of how you LLH would react but try turning the flow temp down gradually say 5 deg at a time and see if the house stays at the desired temp - if it starts to lose temp in rooms and more and more rooms aare calling for heat and not being satisfied you can notch it back up again a deg or two at a time The efficiency gains in a condensing boiler come from the lower return temps Return Temp Boiler % Eff 65.0 88% 60.0 88% 55.0 88% 50.0 91% 45.0 93% 40.0 94% Regarding the cost - depends on size of your house and heat loss Mine is 113 m2 floor area (across 2 floors so 56 m2 per floor) std 2.4 m Ceilings so 290m3 of heated space My heat loss calculations say it's 4.5kW per hour at -2 Last 5 days have been an average of £3.74 per day at 7p per kW in gas (Not including daily standing charge or the 5% vat)

I think that once the boiler starts cycling more than 6 times an hour you've probably wasting more gas on each cycle start up than you are saving with the condensing benefit of a lower flow temperature I can't run lower than 48 deg on my boiler (when the house is close to target temp) because even when range rated down to min (10kW) it still fires for a few secs at 75% of max (18kW) and at anything below 48 it over shoots the set point without really putting a lot of heat into the CH circuit (the min temp I can set the boiler to is 39 deg (38 deg is OFF) As a result I tend to use 55 Flow for house warm up and 48 to 50 flow for when the house/rooms are closer to target temp It's a compromise that I'll resolve in the summer when I replace the boiler for one which can cope with lower flow temps and has a better modulation ratio

Lots of things that confuse me there Modulation Take it off "Automatic" modulation and set the kW ouput to something closer to what you need?? Have you got an installation manual for it - that will tell you how to adjust the kW If the boiler modulation level is 2 - it's got a 10kW min and 30 kW max I reckon these are probably your kW v modulation settings kW Mod Set 10 0 14 1 18 2 22 3 26 4 30 5 With 21 Rads as well as underfloor your circuit vol must be huge I've got 13 rads (no underfloor) and a circuit volume of about 135 L At a cold start that circuit is at around 15 deg C (rough temp of the rooms) without accounting for boiler efficiencies I would take 7kW to raise the water temp in the circuit to 60 deg C Bearing in mind that I have a heat loss of 4.5 kW and I'm using that circuit to heat rads in rooms I want to temp I have the boiler range rated to 15kW because I want the circuit heated to temp quickly but not so quickly that the difference between flow and return exceeds 20 deg which Glow Worm / Valiant Boilers don't like much So I'd be looking at setting it at 3 or setting the kW to 22 to decrease the warm up time Flow and return temps You said "the boiler flow temp reached 61C (d.40), boiler return temp - 52C (d.41)" That's pretty poor in a circuit that size at a flow temp of 65 Deg Set point - as a rule of thumb return temp should be 70% of the flow temp so 45 Deg would be what I would be targetting At 52 Deg Return it's "only just" still condensing - It should be in the mid to high 40's and condensing all the time I hasten to add I know nothing of LLH and the impact on the circuit

Unfortunately you are correct in the main but there are good heating engineers out there - you just need to track them down - my preferred gas engineer is really good but he jokes he's learnt a few things from me about setting up a boiler to suit the house or usage 😉 My 24kW Glow worm boiler is 10 kW min I've range rated to 15kW because 24kW for HW with a 3kW coil is bloody stupid (15kW is still stupid but it modulates down to 10kW on HW real quick) House heat loss at -2 deg is 4.5kW so 24kW for that is mental too but I run heating on timed slots and if I range rate it down to 10kW min the warm up times are extended and what I save in lower and slower I lose in needing longer timed slots When your boiler isn't sized for heat loss and doesn't have a wide modulation ratio (or turndown) life is full of compromises All you can do is work with the parameters you have to try to make the boiler work at it's best in the house it's in PS Glow worms are a rabbit hole as far as parameters go esp ACT settings (Anti cycle Time)

You missed one Is the circuit noisy I'll leave it to the OP to answer - my bet is as soon as a few rads that are too open start to shut down it is PS 14 deg at the boiler at the flow temps stated is not really good at all

Doesn't matter if the hot end is a TRV or a lockshield end (provided the TRV bodies are bi-directional - if they are unidirectional it maters) Were these temps taken during the warm up phase or when the rooms were up to temp? Can you list the rads type/size and the flow and return temps for each rad you are getting If you are counting towel rails as rads they are terrible for having a decent difference between flow and return - at best I can just scrap a 2 or 3 deg difference On your vertical rads do they have diverters built in?

This is when having a good read of the installation manual helps if you have it I think 75 Deg is the default for the heating temp - you can change it in the diagnostic menu d.71 should be where you adjust it All glow worms seem to have differences in how to adjust parameters but fundamentally the process is the same Don't know your particular boiler but on mine diagnostic codes/adjustments to parameters that can be changes is press and hold mode button for several seconds untll you see 00 then + or - till you get to 96 then press mode again you should see d00 Then you can scroll thro using + or - to get to d71 Press mode again and it will show the value - if it's 75 then it's almost certainly the one you want Press - to decrease or + to increase - example change to 60 Press and hold mode to confirm and again to exit (it gets a bit sketchy about this point) To check the setting has been saved start again and get to the same place - if the display shows 60 result it's remembered it if it doesn't try a longer press of mode to make it remember it A proper installation manual for your specific boiler model would tell you exactly what you need to do

Oh forgot to add - on all 11 rads and both towel rails the lockshield valves are wide open - I use Drayton EB TRV bodies - the balancing is all done on the presets. Most Lockshield valves have terrible valve authority which means all of the closing is done in the last 3/4 of a turn - once open more than 3/4 of a turn they are effectively wide open from a flow perspective Have a watch of this video - it will explain why some lockshield valves really don't help you balance the system easily

Sorry but why would you say that? In a well balanced circuit the faster the pump speed the higher the return temp is going to be as you are forcing water thro the rads before it's had chance to shed the heat to the room. You are also using more electricity - for that pump Speed 1 45W Speed 2 65W Speed 3 90W So Speed 3 is twice the consumption of Speed 1 and unless you have a very large circuit you are likely to get a lot more system noise Appreciate that the OP may well not have a well balanced circuit from the original post but you want to balance the circuit with the lowest pump speed possible IMO I'd be dropping it to speed two and seeing if all the rads still get hot - if they do drop down to speed 1 and then just check that when the boiler is firing the temp doesn't overshoot the set point too quickly. Right now my boiler is running at 48 Deg Flow temp - I'm getting a return of 32 - 34 and the whole house is up to temp (11 rads and 2 towel rails) The lower the flow temp you run the lower the delta between the two will be Typically your return temp should be 70% of your flow temp so table below gives a pretty good guide to the delta you should aim to achieve at various flow temps Flow Temp Return Temp Diff 80 56.0 24.0 75 52.5 22.5 70 49.0 21.0 65 45.5 19.5 60 42.0 18.0 55 38.5 16.5 50 35.0 15.0 45 31.5 13.5 40 28.0 12.0 More info can be found here https://www.heatgeek.com/do-we-really-need-dt20/ On warm up I can run the pump on speed 1 but as the TRV's start shutting down the boiler short cycles too much because the boiler overshoots the flow temp set point so I compromised and run speed 2 all the time.

I've got a drain on the flow and return CH pipes that comes from the lowest point under the suspended wood floor and go straight out thro the wall and drain points are accessible via a small hatch in my decking and drain onto the gravel under my decking. only thing that is outside is the drain valve - I really should check one day if either of them actually get warm??? Picture taken before the pipes were lagged and before I put the 75mm PIR insulation above them under the floor Drains valves are to the right to (External to the house) Upper 22mm is the end of the flow and return pipes The pipes going to the left and up and to the left and the feed and return for the last rad on the system The pipework for this rad was a real dogs breakfast as it had been moved from one wall to another and the extended pipework wasn't lagged at all!!! I found similar around the rest of the house when I was under the floor

Why would you turn the lockshields down unless it's to remove the radiator If the system is balanced and you need to remove a rad so close the LS - count the turns to close and note it down so you can restore it when the rad is refitted If you don't want to heat all rooms in the winter turn the TRV down to the frost setting - leave the LS alone No flow at one end is no flow thro the rad

Well the supplier initially offered £30 "compensation" and I could keep the Rad that short circuits - I rejected it and they came back with £50 "compensation" & Keep the rad - I asked at what point they were going to get to agree to replace the rad or refund me completely as that was the only thing that was going to resolve the issue. Replacement arrived yesterday - I've looked in the inlet and shone a torch thro it and there are just 4 pin pricks of light visible so this one should perform as good as the other one which gives a good drop between flow and return and heats up well Not sure what to do with the defective rad but I did find this on the web for £30 ish https://www.bestheating.com/milano-flow-diverter-15mm-inlet-chrome-63476 I reckon if I knock out the blank completely it would fix the issue and I can use the rad in another room (this was my back up plan if the supplier didn't replace it) In other news following reading posts on here by @JohnMo I've been looking at Buffer Tanks to see if I can help to alleviate my Boiler oversize issue TL:DR - Can a HW Tank act as a buffer in when the HW coil is in circuit with the CH Well I've had a bit of a break through but I've thought I've got this damn boiler and heating system sorted before and I haven't but this time I really think I've cracked it. Flow temp 55 Return when TRV's start shutting down is up to 40 Pump speed still on speed 2 ACT (anti cycle time) still 35 (so 14 mins ish at 55 Deg Flow) PO (Pump Over-run) Still 6 mins RR (Range rated) 14 kW Running 55 deg flow temps is fine at the start of a heating period when all rads are calling for heat. I get a nice long heat up burn, rooms warm up and there are no issues but as rooms get up to temp and the TRV's start shutting down the boiler has to wait for 14 mins (ish) due to the ACT setting between burns. If I shorten the ACT parameter the CH circuit is still too hot when the boiler fires it overshoots in under a min. With the ACT set to 35 it gives a decent length of time for the flow temps to drop into the mid 30's so I get a longer burn (2 mins) but it's still not long enough to heat the circuit.... Result is the few rooms still needing heat just don't ever reach target temp as 2 min of heat into the CH circuit isn't enough to make a difference at the rads I really need about 4 to 5 mins of burn for the CH system to get the rad temp up into the mid 40's where it starts to make a difference to room temp. If I drop the pump speed to 1 it makes the burn cycle shorter still so that's not an option If I increase the pump speed to 3 it makes the system incredibly noisy when just one or two rads are in circuit (it's a bit noisy on pump speed 2 but I can live with it) In summary with a 10kW min output from the boiler and a house that is not leaking heat at a fast rate I'm a bit screwed because until more rooms call for heat the last remaining rooms don't actually get any warmer (they don't lose heat admittedly but Mrs BC says they aren't warm). So as above I've been reading up on buffer tanks - they are just an insulated tank with a volume that can be put in the heating circuit to increase the system vol (when rad TRV's shut down and reduce the size of the circuit) I haven't got one but I have got a HW tank (Well a heating coil in a HW tank which adds a bit of volume) Now I know heat transfer is a lot slower at lower temps (ideal way to heat water is high flow temp - large differential - quick heat up) but if I close the gate valve to give somewhere for the excess pressure to go to as the TRV's start shutting down the HW tank coil and circuit can act as a bit of a buffer. Hell it can't hurt So last night I tried it for two hours 3 rads calling for heat plus HW with restricted flow (13% open) system was quieter initially I thought it was a bust as the HW circuit stole a lot more heat than expected but as the tank came up to low 40's it worked much better. HW tank ended at 44 deg. Watching the tank temps (I have probes top and bottom) when the boiler was firing the bottom tank temp went up - when it wasn't firing the temp bottom temp went down - overall the top of the tank was gaining temp over the period. The 3 rads in circuit were a lot warmer (I think they were stealing heat from the tank) There was less system noise Return temp at the boiler ranged between 36 and 42 It seemed like a plan so I left the set up like that for this morning - I lose about 0.5 Deg an hour from the tank overnight as long as I don't over heat it. House warmed up fine 0620 hrs to 0745 hrs (so 85 mins of CH and HW combined) - Tank temp got to 46 Deg in that time and I used a little less gas than previous morning (where first HW ran for 30 mins at 72 Deg Flow to get to 48 Deg and then CH ran for 60 mins at 55 Dec Flow) but that was probably down to having the tank heated the previous night. This evening was going to be the test (OK today was a little milder and we got a little solar gain in some south facing rooms) but to be fairer I extended the evening CH cycle by an hour So 1630 to 1700 Just CH because all rads would be calling for heat for first 30 mins From 1700 to 2000 it was CH and HW together with same gate valve 13% open configuration House felt much warmer went we walked thro the door at 1800 Gas usage From 0620 to 1800 Yesterday 31 kW Today 23.7 kW Gas Usage from 1800 to 2000 Yesterday 12.4 kW Today 4.4 kW Last 1hr boiler activity when CH system only had 2 Rads in circuit - I think best I've got down to before was 3 Rads 4.5 Min Boiler On 13.0 Min Boiler Off (Pump On) 3.5 Min Boiler On 14.0 Min Boiler Off (Pump On 5 Min Boiler On 14.5 Min Boiler Off (Pump On) 4.0 Min Boiler On So roughly 17mins of boiler firing and 41 mins of pump running not firing (4 cycles per hour) and during that hour it used 1.7 kW of gas Return temp never went above 40 Deg HW tank temp went from 40 Deg to 45.5 Deg so not overheating the water but that's a temp I'm perfectly comfortable with. It will lose some overnight as we normally only heat the water once a day but it will reduce the load on the system in the morning when it's a shorter window so it's a loss I can live with. I'm going to see how it goes but it seems promising...........

might as well sling this here My return temps are still too high IMO even at 52 deg flow temps Add to this one of the new vertical rads isn’t heating up very well The en-suite one warms two vertical bars up before the warm water returns via the other six vertical bars Flow temp in 44.0 deg and return is 35.2 so nearly a 10 deg drop The bathroom one (identical to the en-suite) just seems to heat the bottom of the rad and the flow and returns are nearly identical. So I thought I’ve clearly dropped a clanger and fitted it upside down so the flow is short circuiting the rad (there is a blank in the bottom rail that stops this happening) I drained that rad and took it off the wall - shone a torch in the bottom and the blank was at the bottom so I hadn’t fitted it wrong. I was confused and I’m still not sure what made me do it but I looked thro it with a torch on at the other end - this is what I saw https://thumbsnap.com/s/Dgccj4CJ.jpg And from the other end https://thumbsnap.com/s/muHuRPpG.jpg That’ll be a gap round half the blank leading to a short circuit - raised the issue with the supplier as I’m pretty sure that’s the issue with poor heat output and very little difference between flow and return. If I up the flow temp to 70 the rad heats up well but I think thats just a consequence of heat rising much faster at higher temps. Either way I think I’ve found one reason for my higher than expected return temps The other reason was my own fault one rad had been left with the trv body set to six when I thought I’d set it to two. Left the bathroom rad off and isolated - fixed my error on the rad with the wrong setting and hey presto knocked 3 degrees off my return temps compared to earlier in the day when I was checking flow and returns to tweak a few rads that were heating up rooms faster than others

Over sensitive lock shield valves is why I went for drayton EB bodies for the TRV's - 6 available presets does all the coarse adjustment and if you need to fine tune you can use the lock shield (only had to do that on towel rails)

Same way as if the TRV is on the inlet and the lockshield is on the outlet - where the LS and the TRV are makes no difference to balancing IMO if you throttle the flow on the inlet or throttle the flow on the outlet you are still throttling the flow......

That's an approach I haven't heard of before but in my head it makes sense. Any chance of some pictures?

Under floor insulation for me is the biggest improvement in the house in terms of energy reduction - I'm absolutely sure it did the lions share of reducing my annual gas consumption from 15,000 kW to 8,500 kW - however it's built just off a flood plain and has a sizeable void under the ground floor with a lot of ventilation - the CH pipes also run under the floor and the main flow and return 22mm pipes were lagged together which seems nuts from an efficiency point of view 2 16kW units for an 8kW heat loss is madness - it sounds like we will have a oversizing heat pump epidemic and consequences for energy wastage like we did with condensing gas boilers.

It's stated output from manufactures installation and operation documentation - it's a Nuaire unit

I though modern combi boilers could be range rated for CH requirement and have a decent modulation ratio and left un range rated for HW 16 - 17 lpm is a good flow rate for bath taps (compared to my house) can you fit flow restrictor to the hot tap to match the boiler output rate - save fiddling around with taps to balance flow and temp

How big is the extension to double the heat loss and yet comply with current building regs as far as build structure and insulation is concerned!!!!

Don't know how to break up your post to deal with each point so formatting is going to be a bit meh - sorry in advance PIV unit was purchased and fitted because after I installed the PIR under the floor it sealed up the house a bit to much - for the first time in 15 years we got condensation on the inside of the SUDG windows and humidity levels were much higher than before - we thought we'd left that behind when they replaced the single glazing (we didn't get ice on the inside like we used to get with SG but wet windows were a new thing for us) Before PIR living room needed to be 21 or higher to be "nice" after 18 is fine and anything over 20 is way too hot Bathroom rates - I get that they need to be higher but as I said it's not a 24/7 thing - two of us have showers humidity before 60 humidity peaks with extractor on at 80 - after 20 mins with extractor on it's 70 and after an hour with PIV (Extract off) it's 60 again I have tried occasionally forgot to turn on extract and it's not far off same result with just PIV - just the fall off is slower and takes a little longer I'm sure the mcs rules just use worst case - I don't believe using worst case is representative of every house - I'm comfortable with using 0.5 ACH because I know my base line is 0.25 and it's a controlled base line 😉 I've been changing rads for bigger ones (T11 to T22's of the same size) insulating where I can (the PIR underfloor work was a horrid task) but I only had to do it once) and doing a detailed heat loss calc to make sure the house is prepared for a ASHP but I'll probably buy another gas boiler that modulates down to 3 kW (current gas boiler min is 10 kW) before I go ASHP In autumn the house will warm up nicely with a 45 deg flow temp - we will see how much higher the flow temp needs to go in the middle of winter but I doubt it will be as high as previous years where we sometimes ran the boiler in the high 70's

I did heat loss calcs with https://www.heat-engineer.com it was £12 for a one off survey and I had exactly the same issue as you - the ventilation rates suggested for the age of the property and room use resulted in a suggested annual gas usage that was way in excess of my actual Background - It's not a leaky house now, it probably was in the 80's when it was built (Single glazed wooden windows and doors, 35mm of loose fill loft insulation, no cavity wall insulation and a 3 ft void under the suspended floor with an air brick every five.) it's only got three trickle vents, SUDG on all windows and doors, cavity wall insulation, 100 mm of loft insulation under the boarded section and 200 mm everywhere else and the ground floor has been insulated with 75mm PIR between the joists. However I have a PIV unit which is currently set to push in 20 litres per sec which with the volume of the house is equal (in theory) to 1 air change every 4 hours or 0.25 ACH so accepting I will have some other leakage and an increase when I use extractor fans in kitchen and bathrooms or even enter or exit the house I used 0.5 as my ACH per hour rate for all rooms which got my suggested heat loss per hour and annual energy usage to much closer to actual Sure bathrooms and kitchens have a higher air change when you run an extractor but no one has extractors running 24/7 so why would the expectation be that the ACH are 2 or 3??

Imagine if everyone improved their insulation where possible/practical set their boilers up to be more efficient and minimised wasteful running - how much energy could be reduced across the country??? Don't start me off on daily monitoring as it's become a bit of an obsession 🙂 (Having said that coming from a manufacturing background we always say "what gets measured always improves")

In reality I'd reduced it to 16,500 before last winter so 1/2 the previous year usage but still a huge reduction. Annoyingly I replaced the vented HW tank a few years ago (old one needed 1 hr to heat water due to scale inside - hard water area) so it's not that old but I'm sure you are right if I could get a better vented HW tank with a high surface area coil it would probably help a lot when at lower flow temps (at the same time I fitted a water softener so I'm not expecting the same level of scale build up impacting water heating performance) Re-boffins activity - yeah but I'm not a boffin and any of that is probably beyond me.

Combination of both - reduction in heat loss and improved air tightness - the lounge used to be a drafty place - giveaway was black edges to the carpet next to the skirting so it took a fair bit of heating (it's slightly compromised by only having one very big rad for a fairly large room) The airflow under the house is quite a high rate when the wind blows with one air brick every five bricks outside (house was built near a flood plain and the water table is quite high) Of course actions have consequences and one I didn't expect was I had to fit a PIV unit in the house to get humidity levels under control because the lack of drafts meant that occupants created humidity increases that weren't offset by air ingress. Room temp used to target 21 now it's comfortable in the 18/19 area Two rooms have tiled floors which in previous winters would be bloody cold now they are cool in winter but not freezing Hallway and dining room are oak floor over the original chipboard even those floors as I was insulating has improved surface temps. The insulation combined with a few rad upgrades enabled me to get the boiler into condensing mode more often - previously in winter we had to set it to 75 deg flow (so only condensing on part of the warm up phase) not really taking advantage of the condensing eff benefits at all The weeks that were minus temps outside we ran at 68 - rest of the winter 64/65 was fine and I was able to drop it to 60 in the spring. For this autumn/winter/spring I'm targeting 45/55/45 respectively (depending on outside temps) as the remaining T11 rads have now been replaced with T22 or vertical ones The other contributor may be fitting Wiser controls and Smart TRV's but last winter I ran it like an on/off timer rather than a 24/7 with setbacks due to issues I had with heating controls (old sunvic wiring centre with relays) - I think I'll use a little more gas with 24/7 and setbacks but the house will feel nicer as a result. The biggest issue I have with running lower flow temps is water heating - I have a heat only boiler with no facility to set different temps for water heating - I have to do this manually by raising the flow temp for 15 mins of water heating and then dropping it down again for the CH - this quite frankly is a PITA and I'd like to find a way out of this faff. At 55 deg flows I can run HW and CH for a long time and get a high 40's tank temp at 45 deg flow temp I just get a tank full of water at just under 40