marshian

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

Flexicom HX don't have a dial or an "e" position You have "mode" "Digital flow temp display" and "-" and "+" In my case I've already reduced drafts to the point where I had to fit a PIV to manage the humidity gain and In 14 mths I've reduced gas usage from 15 - 16,000 kWh to 8,500 kWh per year.

Apparently if you have X41 on the PCB you can plug in an external temp sensor for weather comp functionality The instruction leaflet below shows what I mean https://www.glow-worm.co.uk/glow-worm/products-1/outdoor-sensor/0020266792-installation-instructions-1476886.pdf I saw you had another PCB that you were experimenting with and I was interested in if that had X41 on the board

Do either of your Glow Worm PCB's have a connection marked as X41 on the side?

Sorry bad habit kWh v kW - I'll try to be more careful I did read all the way thro the thread and as soon as I read your earlier post I though "bingo" but 3 pages on and alternative explanations are still being requested Sometimes the obvious explanation is the right one (still not sure why you would run UFH when you didn't want rads as well but I guess house layout could drive that need)

Interesting thread - really like the calcs on LPM based on kWh, Flow and Return temps - might have to pick It's worth reading the installation manual if you have it - Vaillant Boilers are probably as fussy as Glow Worm of similar era (I have a Glow worm so speak from a little experience although not as a gas engineer) They have a min flow rate (in the case of mine range rated down to 10 kWh it needs 10 litres per min - at 24 kWh they need 17 LPM and at 30 kWh over 20 LPM - if your system can't supply that flow rate at the relevant kWh output then they short cycle or throw faults If your flow temps rise rapidly the boiler hasn't got enough flow or isn't modulating down fast enough (it's more likely to be the former) They also really don't like the difference between flow and return temps to be over 20 deg C so if you wind all the lockshields in to get better delta T's at the rads and then exceed 20 deg C difference at the boiler they will throw faults I range rate mine to 16 kWh for CH in winter and in summer when it's just HW down to 10 kWh - it still puts in more than 10 kWh on restarts but it quickly modulates down to 10 kWh which is still way more than the HW tank coil can take out so on a 117 litre tank it'll run for 10 mins, cool for 6-7 min and then run again for 4 mins before cooling again for 6-7 mins (total HW time 28 mins to get the tank to target temp I've increased the pump over-run time from factory 4 to 8 mins (to try and maximise the cool down time or the boiler will hit target temp of 68 deg way too fast I think your UFH circuit is too restrictive to allow the boiler to be happy - you could range rate it down to min and it might help but it's still going to be trying to shove 6 kWh into the UFH circuit and if the flow is as calculated at 3-4 Litres per min it's not going to be a happy bunny JM2pW

Really good thread this is - I don't envy what you need to do - Ground floor of my house was a suspended chipboard floor with a very well ventilated 2-3 ft crawl space 56m2 of 75mm Kingspan PIR and 3 months work crawling thro a small hole in the floor one of the rooms had it all insulated but a job I never want to do again. I do like your blower set up may have to look at doing that for my house

One more thing - the parameters for anti cycle d.2 don't have much impact at higher boiler temps but the pump over run timer d.1 is set to 4 mins as std (mine was actually set to 2 mins for some reason and used to cycle a lot) - I've now increased d.2 to 8 mins and it gives much longer time for the HW tank to extract out all the heat (once the flow and return temps equalise the boiler with fire again if there is still a call for heat regardless of the pump over run setting) it's around 6 - 7 mins before it fires again

Hi been reading this thread and your "zombie boiler" thread and found them very interesting Trying to keep this post short so I don't ramble on too much but in a nutshell I also have Glow worm Flexicom 24HX and am in a similar boat so to speak When installed it was running for several years at 75 deg flow temps due to T11 rads (legacy from the original house build) and a gas engineer who left the boiler providing enough heat but not optimised (probably never running in condensing mode) the temp was fine for CH or HW Last winter 4 T11's got swapped out for T22's and I was able to reduce CH flow temps to around 64 deg c and returns of around 45 but I had to heat water separately from CH by manually increasing flow temps to 68 which is a bit of a pain to have to do twice daily (return temps don't exceed 54 deg C) tank temp gets to high 40's which is fine for us as we pretty much use all the HW daily and it minimises losses (Tank gets a Legionaires once a week where the flow temp is set to 82 and the tank gets to just over 60 deg C) This summer a bunch of the remaining rads got swapped out for T22's or larger vertical rads in rooms with space issues (bathrooms and Kitchen) Now in the early autumn when CH is starting to be needed I can heat the house with 45 deg flow temps and 30 deg return temps - it may need to rise to 55 deg in the colder months but the return temps will still be lower and keep the boiler in condensing mode all the time. Controls is WISER with Smart TRV's on all but one rad although it now has an automatic by pass in circuit However HW is going to require the same manual work around again this winter so been searching the web for a solution and although I can't find the post I found a thread where an external weather comp sensor was used and small program / switch ran to change the resistance of the outside temp sensor to fool the boiler into ramping up the flow temp when HW was being called for I've found the savings in gas consumption between flow temps at 68 and several cycles compared to a higher flow temp say 75 and one or two cycles to achieve the same temp is minimal especially when the boiler is range rated down Wondered what your thoughts on the Weather compensation hack would be??

Hi All Joined to comment on a thread I found whilst searching the interweb but seeing as an introduction is required thought I'd throw a bit of background down Current house owned 33 years but updated over the years 1980's built detached 4 bed so originally open cavity walls, 25mm of loose fill loft insulation, single glazed doors and windows, void floor downstairs over a 2 - 3 ft crawl space and back in 1991 an annual gas usage for CH and HW of 25,000 kWh two floors with a total of 113 m2 (Small extension done in 2006 to building regs at the time) have reduced over the years with Double Gazing, Cavity wall insulation, upgraded loft insulation (could still be better), new boiler and replacement rads and spent 3 months last year doing 56m2 of 75mm PIR between the joists under the ground floor - amazing reduction to heat loss considering heat is supposed to rise 😉 Currently 8500 kWh gas usage per year for CH and HW but looking to use it more effectively rather than reduce it further