Nest+need new opentherm wiring (keep existing programmer?)

[lucluc]

Thanks everyone for more to think about.

My boiler is an Ideal Logic system boiler, installed this year to replace a very old (G-rated?) boiler, so I don't yet know what my gas bill will be; gas company estimates 550 so I'd hope lower at 450. The only reason I was re-interested in Nest was that I saw it on sale.

The reason I thought OT with lower temperatures would keep the boiler working better/be more efficient is that I read here that OT dropping the temperature avoids the boiler going on and off and instead just keeps the pump ticking over, compared to my existing analogue thermostat shutting it off and then back on again five minutes later. Plus I'd get a few more savings with it condensing.

I'd read the "independent" analysis for the government that analyzed Nest in 2017 vs houses with normal programmer/trv/thermostat and it said it saved 7% of heating (5% overall gas usage), and an extra 4.5% with the optional savings programme, with a break-even around 4-6 years.

However, I completely agree with the fact that my life is not so exciting that I suddenly need to heat the house while on the bus home, and people who leave heating on and then leave the house, well, how do they cope with cookers and taps?

And Google don't have the best reputation for maintaining products...

But having got a boiler with OT it does seem a shame I can't then use the feature. Evo seems far too expensive for me to break even.

Perhaps instead of looking for savings from a new thermostat, I should keep the money and look in to replacing the old copper HWC (75"x12") instead since I read that the new ones keep the heat for days.

 

[vulcancontinental]

Running boilers cooler makes them last longer is unproven, just a theory backed up by a logic. When the old boilers ran hot they cycled much more and lasted 25 years plus. You have a cast Ali heat exchanger which will need more thorough servicing if condensing more and will last longer if run hot. You'll save more money by insulating any exposed hot pipework in the airing cupboard. I attended a meeting of clever boffins from the BRE years ago who had run trials and I wish I had written down the figures but I was very surprised at the size of savings. The size of you bills are small, 3% of £500 is £15 if the esrimate is accurate but it does seem low. It's more fuel efficient for your boiler to cycle 3 times an hour with a 5 minute anti cycle delay than for it to run continuously at low temps condensing. The 15 minutes of non-fuel use saves more than condensing the water vapour in flue gases.

 

[Dan Robinson]

Running boilers cooler makes them last longer is unproven, just a theory backed up by a logic. When the old boilers ran hot they cycled much more and lasted 25 years plus. You have a cast Ali heat exchanger which will need more thorough servicing if condensing more and will last longer if run hot. You'll save more money by insulating any exposed hot pipework in the airing cupboard. I attended a meeting of clever boffins from the BRE years ago who had run trials and I wish I had written down the figures but I was very surprised at the size of savings. The size of you bills are small, 3% of £500 is £15 if the esrimate is accurate but it does seem low. It's more fuel efficient for your boiler to cycle 3 times an hour with a 5 minute anti cycle delay than for it to run continuously at low temps condensing. The 15 minutes of non-fuel use saves more than condensing the water vapour in flue gases.

Back when I was running my thermal store, hooked up to a laotop; I could see in real-time the heat leaching from the tank through the uninsulated pipes. They were soon insulated.

 

[lucluc]

Thanks for the info, I didn't realize that the aluminium plates would corrode more at lower temperatures when condensing; with one post suggesting the Ideal training course said theirs lasts ten years. Great. So, in fact, connecting OT would request lower temperatures by default, thus causing more corrosion and potentially earlier failure.
So, is it actually worth running the CH in eco (67C) or just twist the dial to max? At 67C, is it just say 1% extra condensing efficiency so 1% max saving on gas bill, but at the cost of potentially earlier failure?
My bills are quite low (according to the "compare to similar properties" on the gas bill), I think it's because we got a very good deal years ago on external insulation at a 100 pounds for the whole house! (local government negotiated some bulk deal and opened it up to everyone on first-come first-serve, otherwise I think it's around 80 years to break even).
Every pipe I've access to is insulated, but I don't know about under the floorboards until we need to re-carpet. I'm guessing not since it probably wasn't common back then, but I'll insulate as much as I can when I have access since it should make heating the hwc a little more efficient.

 

[vulcancontinental]

I don't want you to overstate the matter, the casting is thick and ali, it will form a protective coating against corrosive condensation, all this means is there will be a need to physically clean the exchanger with a brush and lean the sump each year if it condenses more. Ali is far more conductive then stainless steel and it will happily run shifting more of the sensible heat in the heat exchanger from flueside to waterside than stainless steel or less efficient material combinations and there is over 10 times more sensible heat than latent heat released by condensing. There's been a slow whipping up of a craze for condensing mostly actioned by the manufacturers of the less efficient heat exchangers. A condensing boiler is a lot more efficient that a non condensing boiler but to achieve that improvement it only has to be constructed to remove enough sensible heat to offer the opportunity to to condense ,it is not a necessity.