marshian

Oh please tell me how the chuff that works maths wise

@Dee Have you got an ABV in the CH system or do you run a couple of rads with no TRV intervention? I was just thinking that if you do have an ABV if it's set a little too free that could also 1. drive up the return temp 2. Lower boiler efficiency 3. Cause furthest rads in the CH circuit to be cold ABV - Automatic Bypass Valve

so Future Homes Std was planned to ban sale of gas boilers in 2035 so like for like replacement would not gave been possible https://eciu.net/media/press-releases/2025/plan-to-scrap-gas-boiler-ban-comment https://amp.theguardian.com/environment/2025/jan/06/uk-government-scraps-plan-to-ban-sale-of-gas-boilers-by-2035 I reckon a few ASHP manufacturers aren’t going to be happy

I have a monthly club meet 2nd Wednesday of every month so I think most months I would be OK and not have two meetings in same week IP24 so Breckland Area (ie I'm Suffolk/Norfolk boundary)

@Dee Lets go back to basics - it's not a test just a few statements to develop understanding of the point of balancing and the benefits. So at a boiler flow temp of 60 deg and a well balanced system Heat Geek table of earlier would expect a return of 42 Deg (You currently have a return of 50 Deg so that's a bit higher than would be expected) So if it's a bit higher then there can be a few potential causes 1. Pump speed too high - water is being pushed thro a rad (or rads) too fast and being returned back to the boiler before it's had chance to release the temperature into the room. or 2. Too much flow thro a rad (or Rads) leading to water being returned to the boiler too soon (AKA Poor Balance) or 3. Rads too small for the heat output required for the room so flow needs to be quicker to raise the mean temp of the radiator to get the room up to temp Why is return temp important for efficiency - well if it's a condensing boiler the efficiency of the boiler improves the cooler the return temp is So currently your return is 50 deg so from 50 C at the bottom scale (Return Temps) go up to where it hits the yellow line on the outside of the curve and then go horizontally left and you get 91% - that's the efficiency currently of your boiler when its running with a 50 Deg C return temp Now follow the process taking my return temp of 25 deg and go up to the yellow line on the curve and then go horizontally left and you'll see that it's about 97% efficient So about 6% improvement (or reduction in gas usage) that's my payback for over sizing my rads to be able to run lower flow temps and buying a boiler that can actually run happily at those flow temps without cycling (My old boiler min flow temp was 39 but realistically the lowest it could actually run was 45 and even then it cycled) Now if I have a target room temp of 20 Deg C in a room no matter what the flow temp I am never going to see a return from a radiator in that room below 20 deg it's only going to be above So If I'm feeding a rad with 30 deg and even if it's a massive rad the minimum temp leaving the rad is going to be 20 deg or more - this is why as the boiler flow temp is lowered the difference between flow and return is always going to get narrower. So this explains why my drop between flow and return on all my rads is so much narrower or lower than yours. The difference between our boiler flow and returns is because I'm running a flow temp that is 50% of yours. Now lets look at what we want to happen across all the rads in the CH circuit - we want them all to release heat into the rooms - as heat is released the rads get cooler and as a result they all contribute to the drop in the return temp back to the boiler but the return temp is going to be impacted by the level of flow thro each rad Example (with easy Math) CH system with a flow of 10 Litres per min 4 rads in circuit all being fed with 60 deg water All the rooms are the same size All the rads are the same size So in a balanced system each rad gets 2.5 Litres a min Each rad has a temp drop of 18 Deg C The return temp to the boiler is 42 deg C (Ignoring any losses in transmission pipework) Now lets show the impact of "inbalance" in the same circuit everything in Bold above is the same Rad 1 gets 2.5 Litres a min - In 60 out 42 Rad 2 Gets 5 Litres a min - In 60 out 54 Because Rad 2 took 5 Litres per min the remaining rads can only have 1.25 Litres per min each Rad 3 Gets 1.25 Litres a min - In 60 out 40 Rad 4 Gets 1.25 Litres a min - In 60 out 40 What's the temp of the water back to the boiler?? 25% of the water is at 42, 50% is at 54 and 25% is at 40 The answer is going to be more than 42 - probably around 47 if my back of a fag box maths is close As a result efficiency of the boiler drops from 93% to 91% a difference of 2% all because one rad was providing the easiest path back to the boiler Those rads with very narrow differences between flow and return are my concerns in your circuit - as I've said before Water is inherently lazy it will always find the easiest path to get back to the boiler

Your house is over twice the sq m. of mine.... My House has 75mm of insulation under the suspended wooden ground floor, Double glazed windows, Back door and front door all from 1994 (The two double french doors are from 2019 and are to modern stds) Brick external skin construction, breeze block inner with a 50mm cavity filled with blown insulation Cold roof and just 100 mm of loft insulation PIV unit with a heater (not used) not MVHR Heat loss calculated is 4700 w at -2.4 deg C outside with an internal temp of 20 Deg C Annual Gas consumption for CH and HW is 8900 kWh and Electric is 3500 kWh (No electric heating) so annual total cost for both is £1644 at current rates £2677 doesn't sound bad but I bet your heat loss calc is less but the bigger the property the more heat will be lost The issue for me is MCS approved suppliers do not want to end upcoming back to fit a bigger ASHP when the house doesn't reach target temp and they aren't going to be the ones paying the bills for the running costs................ As a result they oversize

You have 10 rads in circuit where the DT is 10 or greater (That's pretty good depending on the rad type) You have 6 greater than 12 (one is 16!!!) My only conclusion is your maths is quite poor 😉

I'm running a boiler flow temp in very low 30's You are running a boiler flow temp of 60 deg I heat 24/7 with no setbacks - I am assuming you heat to timed schedules or 24/7 with set backs day and night The boiler flow and return difference as well as individual radiator difference between flow and return are always going to get narrower as the flow temp drops Heat Geek sourced https://www.heatgeek.com/do-we-really-need-dt20/ 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 You use the same clamp to measure boiler flow and return too? Clamps are a bit hit and miss especially on pipes - better to use and hand held IR on rads - they aren't expensive and it's a lot quicker as with pipe clamps you have to wait for the temp to stabilise Don't measure rad temp in the middle - you'll get random results - Top Middle OK but not centre of the rad OK be good to know which rads were Towel Rails rads because they are terrible for acting like a great short circuit and returning HW straight back to the boiler and starving other rads of flow without appearing to do that. OK were all rads calling for heat ie TRV's wide open? I'm not technical but I am a bit data driven............. We all want a warm house and bills that don't make us cry 😉

Me trying to make sense of it (It's in the same order from top to bottom but I've fixed where flow and return were wrong and worked out the DT Normally I'd say if the DT (Difference between flow and return was small there would be too much flow thro the rad but if the rad concerned is a towel rail then all bets are off because they are terrible for getting a decent drop between flow and return (they aren't much good as a heat emitter either IMO) B. Flow 60 B. Return 50 Rad Flow Rad Ret DT Rad?? Comments 54 43 11 45 56 45 11 44 54 38 16 41 44 40 4 45 What sort of Rad? 57 45 12 45 52 45 7 46 55 40 15 40 54 40 14 43 54 51 3 50 What sort of Rad? 43 29 14 30 55 43 12 47 55 47 8 49 49 39 10 39 57 46 11 46 54 46 8 44 49 47 2 44 What sort of Rad? 52 47 5 ?? What sort of Rad? 44 41 3 40 What sort of Rad? 41 39 2 39 What sort of Rad? ?? ?? ?? ??

Just to clarify - the boiler was no longer on a burn when the last radiator (Lounge) Flow and Return temps were taken and that rad has the highest flow rate of all the rads at ~1.2 Litres per min so it doesn't take long for the flow side to cool quickly Also to add Everything before Bed 1 is downstairs Circuit and after Front Hall is Upstairs Circuit - the whole house is one Zone for CH Every radiator has flow restrictions in the TRV body and lockshield wide open I have a fairly good understanding of the flows to each rad

So from left to right it's Rad Flow temp - Rad Return Temp and Rad Temp? Rather than order they heat up in which is notoriously difficult to get - could you annotate them with Upstairs or Downstairs and Label them with the room Here's what I use

Lot of data there to dissect but I'm going to start with the obvious - the TRV end might not always be the flow end Example flow of two of my rads would mean the TRV would be tucked in a corner rather than in Free Air so more likely to turn the rad off before the room has reached temp so I deliberately put the TRV on the return end So I would suggest that if you have a hotter end on the lock-shield end then that is the flow end and the TRV end is the return. Second point - how are you measuring the temps (ie with what and where are you measuring on the rad) I take 3 temp readings from every rad (all my rads are BBOE rather than the more efficient TBOE) with an hand held IR 4 of my rads are anthacite the rest are white and I get better readings from the dark rads - I did put black insulation tape on some of the white ones to improve accuracy but Mrs Marshian didn't like that approach at all. Flow inlet - ie bottom of the rad where the flow pipe enters the rad Top Middle - middle of the rad at the top Return outlet - ie bottom of the rad where the return pipe leaves the rad I take 3 measurements because depending on what the TRV is doing and what the boiler is doing often the middle top is the best guide to actual flow temp (Hot water rises so often the inlet area is actually slightly cooler) If I can format the results I'll share the readings I took from earlier this evening Bear in mind (when I share the results) that this evening I was running a boiler flow temp of 32.5 Deg C and the return to the boiler was 25.0 Deg C Even when I was running scheduled heating and 55 deg flow temps I could only get a couple of rads to beat 12 Deg C drop between flow and return and they were big 1400 x 600 T22 (Double panel double convector) rads

Don't have a vaillant boiler but I'm liking the deep dive on settings and the experiments - great stuff guys Commenting so I can add the thread to content I follow

Excellent - hopefully this level of control will soon move into the heat only boilers - currently they are still a poor 4.7 to 7.2 when used at low flow temps

Nice to see Vaillant finally getting closer to Viessmann on the lower range of modulation - Well they aren't there yet but the gap is narrowing 4.0 v 3.2 at 40/30 range I hope that's real rather than claimed

Pretty sure the UK used an above 100% rating when early condensing boilers came in - heat geek did a video on it a while back explaining how it was worked out - it'll be buried in a video somewhere and I'll have a go at finding it

It's a conversation being carried out elsewhere on here - Smart is not always "smart" sometimes it's pretty (expletive deleted)ing dumb

Sorry meant to also say it does show that there is an impact on efficiency until 60 mins of run time (OK so it's the outer edge of a bell curve) IMO it's still over 1% (but less than 2%) loss at a 3 min run time which is why I like to set the system up to minimise cycling as much as possibe

That is an excellent result but maybe way outside the abilities of most people All I’m trying to do with this boiler is get it running at it’s optimum when matched to the house needs using the parameters that i have control over - I think I’m fairly close to where it’s doing decent length cycles at low flow temps and maintaining the house at a comfortable temp without burning excessive amounts of gas.

I've seen that before and I reckon it's flawed because it doesn't take into account the increase in modulation on start up - my old glow worm boiler took 4 mins to drop down to 10 kW from it's fire up at 85% of max (which is actually fairly typical of many boilers)

Absolutely correct but it's not hard to log the totals by day and as a result get the daily number of starts Or perhaps that's just me being typically OCD

I had mine set to an "oil boiler" before I went 24/7 that tempered the Wiser unit from intervening as often

So twice the size of mine 😉 and with 21 rads a much bigger CH circuit. Any heat loss calcs been done or have you done one yourself? This company link below have an online one that I used and found it fairly straightforward - I made a few mistakes - so check and check again before submitting to get the report - the detailed report at the end of it was pretty comprehensive and the few mistakes I made I could manually correct for. https://heat-engineer.com/en/ You really only need a tape measure and a reasonable understanding of the fabric of your house and can match it to the selections available - took me a couple of days to go thro the house room by room I wouldn't ever make a boiler purchase without knowing or having a damn good idea of my potential heat loss so I can size the boiler correctly (I made that mistake with the previous boiler - not enough research and just thinking that can't go wrong with bigger cos bigger is best right!!!!) For the new boiler I could have got away with an 11kW Heat only Viessmann but as the 16kW version had the same min output I chickened out - I was also still heating to a schedule rather than 24/7 and you need a more ooomph to get the house back up to temp quickly) In fact all the Viessmann Heat only boilers from 11kW to 32kW have the same 3.2KW min output (only the 11kW to 24kW fit inside a 300 depth kitchen cupboard - the 32kW is much deeper) Turns out that the 11kW version can't be range rated and the 16 kW version can so I got lucky there by accident rather than good research

Warning - I may or may not be a little OCD on data collection and evaluation Todays statistics House Internal temps 18 - 20 deg Outside temp C Lowest -1.9 Highest 2.3 Average 0.2 Highest Boiler flow temp on CH 34.4 Highest Boiler return temp on CH 27.1 Currently 34.3 deg C flow temp CH has been on for 14 hrs, HW for 30 mins so far today so total mins 870 mins Total boiler burn time 600 mins Number of starts 11 So boiler run time is 69% of the heating on time and average boiler burn time is 54 mins (Would be higher but it did 30 mins of HW and it always stops and restarts after doing the HW due to the 80 deg flow temp mandated by the HW Demand box)

I can accept a level of cycling - less than 3 per hour would be my aim It's not just the efficiency loss from excess cycling it's the wear and tear on the boiler components, expansion contraction, gas valve, igniter etc etc Old boiler peaked at 24 burns in an hour and I got a cooling house as an added bonus (don't over zone and don't try to achieve the biggest drop you can on each radiator flow and return were lessons learnt there) New boiler set a record of 53 cycles in 8 hours per hour but that was down to 13 Wiser smart TRV's all having the ability to individually fire the boiler They don't get to do that now