marshian

Very interesting - well documented - I'm not yet ready to go ASHP but I do need to replace the boiler because it's oversize 24kW for the house demand and the short cycle issues waste gas and annoy me even though I've range rated it down to 12kW. The new one will solve a lot of the short cycle issues but spring and autumn will be a challenge when heating required will be less than it's minimum We also prefer to cook with gas so going ASHP (with a grant means we lose that)

I've been data logging the house internal Temps and Humidity as well as the Loft (cold loft relatively well ventilated) Temps and Humidity for the last 10 months but I've spit the data into day/night (based on daylight hours as solar gain has a big impact on loft temps - south facing roof) I did this as I don't have MVHR and when I insulated under my suspended floors to reduce heat loss I saw a spike in humidity levels - I fitted a PIV unit to reduce humidity levels and I've been logging data since It's still not as low as I'd like but it's definately improved the feel of the house.

Very difficult to find the full specs of those atag boilers especially modulation or turndown ratios

We have a suspended ground floor with a sizeable void under it - I've insulated it and it made an absolutely massive difference to heat loss in the house - 4.3 was with an ACH of 0.5 - with default ACH it was around 6 from memory (this winter we were able to validate the 4.3 over a few days when it was around -2 for the whole period) Flow and return are 22mm with short 15mm tails to the rads and I have TRV4 bodies on the rads to adjust flow rates Viessmann 200 isn't suitable - won't fit the desired space - current boiler is 2 pipe flow and return at the top and I don't want to rip floors up to re-pipe for a 4 pipe set up - the difference between 1.8 and 3.2 isn't enough to convince me the upheaval required is justifiable Minimal change to the system required to go to a 100W heat only although the quote I got from the only Viessmann installer in a 50 mile radius is more than expected I'm still going that route. I tried setback with current boiler - it cost way more to run than scheduled heating times (almost certainly due to boiler min kW) I will try it again with Viessman when it's installed. I should add I'm installing with existing vented HW system due to not trusting 30 plus year old pipework with mains pressure I've already found 2 poor joints in the 30 years we've lived here and all the upstairs CH pipes run in the void between the floors and are quite tricky to get at.

I used this https://insulation4less.co.uk/products/tubolit-polyethylene-pipe-insulation-all-sizes I tried to get the OD of both 22mm and 15mm pipe insulation to be the same so I could set up the pipe lagger tool to work with both sizes so that I didn't have to constantly change the width of the cutting box

Looks like they've insulated flow and return together in one bundle - That was done in my house too - I've stripped it all off and insulated each pipe separately - made a massive difference to the return temps at the boiler as there was clearly some heat being lost from the flow to the return pipe driving down the delta at the boiler

If you can read a tape measure and know the construction of your house and the std/age of the double glazing you can do the heat loss calcs for a days work using https://heat-engineer.com/home for a one off fee of £12 I've done it myself early 80's 4 bed detached house (with some 90's insulation upgrades - SUDG, Improved Loft insulation etc) My heat loss at -2 came out at 4.3 kWh - current boiler is 24kW with a very poor modulation ratio (min 10kW) the heat loss explained why it cycles so much as even at -2 it's trying to push 2.5 times the heat required to maintain house temperature. We only have a few days a year at -2 most of the time it's 8-10 deg at which point it's trying to chuck 6 times the heat energy required to maintain the house temp. I've experimented over the winter with flow temps and with the current boiler I can get down to 45 - 48 deg flow temps - however this is mainly due to 10kW min input and a boiler min flow temp of 39 deg C and flow rate of 10L/Min I've also experimented with range rating the boiler to try to replicate what life would be like with a 11kW boiler and the warm up time is a little too long. The heat engineer software has told me exactly what each room needs to maintain a 20 deg room temp and I've been thro room by room sizing the replacement rads to run lower flow temps in preparation to a boiler change this year. (Viessmann 16kW - 100W heat only boiler which will be set up with DHWP and weather compensation - Yes I could go for the 11kW version but the min rating of all the 100W boilers is 3.2 kW so nothing lost by going for a little larger, we heat the house according to a schedule as we are at work during the day and slightly larger improves warm up time) So in summary 100% recommend a good heat loss survey Size your boiler (and rads) according to the way you heat your house and how quickly you want your water recovery to be - if heating constant (low and slow) you can size the boiler to be smaller - if heating according to a schedule you are going to want the boiler to be slightly oversize to get quick recovery of room temps

Ahhhh now that makes perfect sense - it did that once so I've set up my wiser so the "base" temp is only 7.5 deg. Unless a room reaches that temp when it's not scheduled for heating it won't fire the boiler and it's only the front entrance hall that's ever likely to hit that temp so for that TRV it's set to "off"

I know that - the question was directed to MrPotts as he's reverted to manual TRV's having had smart ones From my perspective a smart TRV does have a one advantage over a manual TRV - If a member of the household (I'm looking at Mrs Marshian here) turns it up because she thinks the room will warm up faster...... after 1 hr it reverts to it's previous set point (a Manual TRV stays there till I realise a. the room is too hot or b. I've burnt a lot more gas than normal)

Whats the difference between a smart TRV and a manual one - they do the same thing Always happy to learn something new

Yikes - that's a seriously hot boiler HE core to trigger that............

I know this an old post and I agree with the point made about using Viessmann controls I don't think there is a huge saving to be made. I've fully invested in the Wiser system and since Sep 22 I've replaced all the rads and optimised the sizes to allow me to run much lower flow temps. The individual room temp settings and the scheduled heating times are now spot on for what I need. I don't have any UFH just rads and one heating zone. However with a house heat loss of 4.5 kWh at -2 and a 24 kW glow worm boiler with a min output of 10 kW it's rather over sized for the house and I don't have weather compensation on the boiler so I currently manually set the flow temp for the weather conditions - I run anywhere between 42 Deg C and 58 Deg C flow temps but for HW requirements I have to manually increase the flow temp and turn off the CH whilst HW requirements are met. Later this year I will replace the boiler with a Viessmann 100 W in DHWP mode, Allow the CH Temp controlled by a Viessmann Weather Compensation module and leave the Wiser system and all the smart TRV's in place. I'm pretty confident that this will work nicely provided I get the curve right. If I find that it doesn't work as well as I expect I'll dump all the TRV's and run fully open system but I think my plan will work just fine. I don't see that the Viessmann Controls for CH give me any advantage over the Wiser and I have no intention of trying to use the Wiser OT to control the boiler flow temps as I don't think it's as accurate as a WC temp sensor on my house wall.

I agree it's very clear what the issue is............ Establishing if the issue affects CH is quite easy - just park yourself in front of the boiler when the house is up to temp and most of the TRV's have shut down. Observation is often the key to seeing whats happening - it's almost certainly doing the same - it's just with a massively elevated flow temp the recovery time for the boiler from the fault timer isn't taking a long enough time to cause the house to cool down because the rads that are still in use have to cool down from 82 deg flow temp and that'll take a while....... So the engineer has given an option that has been demonstrated to stop it happening - you don't want to take up that idea. The "agreement" of the engineer that is shouldn't need you to change your house heat behaviour and the boiler should be able to cope with how you want/need to live is because he recognises you aren't going to change no matter what he says, You are convinced it's the boilers fault - it's his "get out of the situation" because he is unable to educate you out of the issue. He knows full well WB wouldn't entertain replacement of the boiler for the situation you force the boiler to work under. To be blunt - it's a situation of your own making.

Abso-f*cking-lutely this It's like choosing an F1 car for a city commute or a Bicycle for an F1 race it's just nuts and because it's so nuts the boiler doesn't like it and says thank you - goodnight

I'm frankly amazed that any house needs 82 deg flow temp for rads - your heat loss must be horrific Even 70 is high for spring, summer and autumn - the boiler is barely into condensing mode. Does the HW issue occur when you are running at 70 deg flow temp for the CH in spring/autumn I'm currently running radiator flow temp at 55 today I only need maybe 2 hrs of heating this evening - I could run it longer at lower temps but 55 gets the house up to temp a little quicker.

Appreciate the pedantry - thanks

Our electricity usage is pretty constant (Gas Central Heating/Water not ASHP) 4 bed detached - 2 occupants Our background overnight usage is 250w per hr (2 fridges, 1 freezer, CCTV, skybox, router, signal repeaters, microwave clock and a load of smart items that all consume a little) Daily consumption overall varies from 7.0 kW to 13kW at the weekends (washing days, tumble drier and oven usage are all quite large consumers) Point I'm making is usage overall will mirror ASHP as for most houses the usage is pretty constant and I can see why you would put the case that it seems to be double the declared ASHP usage. Summer time when space heating is not required should give you a good guide to your base line usage?

I don't want to be antagonistic here but have you attempted to see what the house actually needs flow temp wise for CH for a reasonable speed warm up and at a steady state? Your old 34 year old boiler would have been fixed output, no modulation and minimal temp control - it would have also been chucking energy out of the flu. Yes they do heat houses quite well but are very inefficient compared to modern condensing boilers - I'd have a guess that you've seen little or no saving in terms of gas consumption since the new boiler was installed.

I've just watched the video and seen that............. And agree with earlier comments that is bloody high for a CH flow temp - have you got tiny rads with no convector fins? Mine is an 82 build house, std CWI and 100mm of loft insulation and 30 year old double glazing and even before improvements to the original rads 68 deg was more than enough CH flow temp for the 13 rads in the house only in a prolonged period of minus 5 did I raise it to 72. 82 is boiler flat out?? It's a condensing boiler and you are running it like an 80's non condensing boiler and at 80's efficiency levels - return temp must be 56 at best so only in the initial warm up phase (which will be bloody short) will it even condense.

What is your flow temp for CH? I assume no weather comp (and you don't manually weather comp by changing flow temp depending on the weather)

I'm sure you are right but just to say about 25-28 years ago there was a push to get more households off rateable value based water rates and onto meters - one of the incentives offered in my region was pipe coverage from the meter to the house stop cock for as long was we were in the house (it expires on change of ownership) We got a saving of 50% of our previous water costs as a result of fitting a meter. I've been very careful to keep the letter in my water bill history file. It would be interesting if I ever did have a leak to see how the water company would react - my money says that they would say from the meter to the house it's my responsibility but that letter might provide an interesting leverage and whilst I haven't needed it yet I think they'd have trouble backing out of the responsibility.

Never seen one but then I haven't looked that hard

Agreed - it takes me a lot longer but I get what I want to the std I'm happy with And the next time I do something similar I do it even better having learnt from the previous

Looks identical to ones I have fitted It's a std button type like this - has a slotted shaft to lock on the cable mechanism and the pusher comes out of the middle https://www.screwfix.com/p/flomasta-dual-flush-push-button-chrome/674fy If you want something different then you may need to evaluate if it will work

Absolutely - My boiler is 5m from the HW Tank - the pipes run inside the heated envolope of the house (between the ground floor and 1st floor) but are not lagged and I lose 2 deg of flow temp between the boiler and the HW Tank When the kitchen gets replaced this year the ceiling is coming down anyway so both flow and return pipes will get lagged then