marshian

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