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Turn the flow temp down if you can, 50 or 55 degrees.

Cycling is way worse with the WC curve down any lower.

Should probably say that we been having -3C overnight and 0C days here.

PSA the ideal logic is absolutely crap, at least it does have a SL2 that forces a priority hot water call at 80C.



Give the state of the install so far it's very possible I'm fighting some underlying issue that I don't know about.

Whats your daily gas consumption at the moment ?

60-80 kWh a day.

In the milder weather (8C) it was about 40 kWh a day.

Charging the hot water tank is about 10kwh a day. (I charge it with gas since it's cheaper than electric export).

Plumbing wise, a cheaper bodge could be to encourage the boiler to "long cycle". Basically, fire the boiler until return temperature to the boiler gets so warm that the boiler cuts out.

Then continue to circulate the hot water around until it reaches some lower temperature. And repeat. Essentially add more hysterisis to the system.

Should be achievable with basic thermostats, relays and a bit of canny wiring.

We have an old boiler, (not over-sized, just designed to provide background heating throughout the house) fitted when I/we installed the GCH 40 years ago. I have looked after it - but not obsessively - and I can't get the boiler drain-cock open to de-sludge it (and I am afraid that If I apply too much force I shall wreck the boiler water space!) I have used corrosion inhibitor and (twice at least) put cleaning solution in and have heated and circulated it, plus draining down loads of indian ink from all my drain-cocks - except the one on the boiler, obviously. I suspect I am also paying the price for an even more inefficient boiler than we first installed!

My boiler cycles, bumps and is clearly not well (I suspect because the gas is only actually heating water in the the top 1/3 of the water-space) but I daren't get any more aggressive with it until the spring when we shall be able to do without the heating! I suspect that the only solution will be a total replacement before very long...
A

Swwils wrote: ↑Wed Dec 07, 2022 8:17 pm 60-80 kWh a day.

In the milder weather (8C) it was about 40 kWh a day.

Charging the hot water tank is about 10kwh a day. (I charge it with gas since it's cheaper than electric export).

Sounds like your house is a good candidate for a heatpump, I was on at least 100 kWh /day at this time of year on gas CH.

Problem I have is that most rads are on 10mm poly runs of quite significant length.

I'd be happy to bung in a heat pump myself, can't be that hard.

There's something wrong here, I think, If your boiler is modulating down to 6kW or so that consumption figure would imply the burner is firing for more than ten hours a day!! Does that seem likely to you? Have you checked the gas rate while it is firing?? that could be revealing.

Desp

Swwils wrote: ↑Wed Dec 07, 2022 8:50 pm Problem I have is that most rads are on 10mm poly runs of quite significant length.

I'd be happy to bung in a heat pump myself, can't be that hard.

I self-installed an ASHP here, Got very fed up with getting ludicrously high quotes for an MCS install (cheapest was around £6K). Bought a brand new ASHP for £1,700 (inc VAT, delivered) , spent around £300 on pipes and fittings and had it up and running a day later, never having seen one before.

Only two key things I learned were that they MUST have large bore pipes, they will throw a flow error unless the overall flow resistance is very low, lower that that for a typical boiler (easy fix is to fit a low loss header). Other point is that mine came with default settings that were hopeless for the UK climate. Took me around a day of fiddling about to get the settings right and get the efficiency up above the 3.5 mark.

Other than that is was a lot easier that installing a boiler.