Running boiler at low temp

[Mike Faithfull]

So, here we are with nice shiny new boiler, system all de-sludged, TRVs on the rads, the works. Because CORGI man wanted the flushing chemical circulating as much as possible, I kept the boiler on continuously and the room stat set to 23 degrees. It was a hot few days, but now the system has been drained out, flushed and inhibited, I've discovered that setting the room stat high to keep the pump running continuously, but setting the boiler temperature control low produces a nice evenly warm house with no cold spots and is much cosier than having the pump stop and start as it does with the room stat set to a 'sensible' temperature and the boiler set to produce water at a high temperature.

The question is: "is this a) bad for the boiler, b) inefficient, c) costly, d) any combination of the foregoing?" (Subjectively, the boiler seems to be off for very much longer than it's on, so I don't think I'm burning lots of gas, but I'd rather not wait until the next bill arrives to find out I'm being a Silly Billy!) It's a minimal pumped heating convection hot water system, by the way - no motorised valves etc.

[Andy Hall]

If it's a conventional, non-condensing boiler, then this may be a bad idea. They are designed to operate with 82 degree flow and 70 return. If you turn down the boiler thermostat to the point that the return temperature falls below about 54 degrees then you will get condensation and eventually corrosion inside.

If it's a condensing boiler, then this is a very reasonable thing to do. The lower the return temperature, the better from the efficiency standpoint. In this scenario, you mainly need to be sure that you have the temperature high enough to deliver enough heat when its cold.

[Doctor Evil]

If non-condensing boiler, then buy a clamp on thermometer and put it on the boiler return. If it never goes below 60C, it is fine. If it is a condensing boiler then you have cracked it and it may be wroth lowering the temperature as long as the DHW does not suffer. What boiler do you have?

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[Ed Sirett]

You have found the setting on the boiler which heats the house in the current weather conditions. It also manages to provide sufficient HW for your current requirements.

The pump will consume a fair bit of electric over the course of the winter and there may be some saving by having it on less. You might be talking about saving £5-10 of electric on the pump.

You don't say shat sort of boiler you have had fitted? if it is open or balance flue then it is much less efficient to run it all the while as the warm water in the primary circuit will be cooled in the boiler when it's not firing.

BTW On what grounds did your fitter replace the existing heating system with something that is not to current standards? Where is the control of the HW temperature?

[Mike Faithfull]

(snip ..)>

Thanks for all replies - the consensus seems to be 'good idea for a condensing boiler, bad idea for mine' (Potterton CFL60 replacing old Potterton CF60). Having worked in the electronics industry for a good few years, I am reasonably adept at guessing the temperature of metal surfaces (from touching heatsinks and hot power transistor cases!) I can just about manage 60 degrees for a second or two before it becomes too uncomfortable. I would bet that without measuring with a proper instrument, the return water temp is below that and the feed not much above, so I've turned up the boiler temp and turned down the room stat as advised.

The lack of compliance with current standards is entirely down to lack of money, Ed. It was all carefully explained to me, and he gave me leaflets to back up what he was saying, but I simply could not afford to do it all in one go. I need a new cylinder, a tank stat, motorised valve and new room stat at the very least, but could not afford to do that on top of everything else. He said he would fit a replacement boiler, flush out the system (which was sorely needed!) fit TRVs and replace an under-sized combustion air vent to give me a system that would work better and safer than before, but only on condition that I signed a 'disclaimer' letter to the effect that I chose not to make the system compliant at this time against his advice. I do, as it happens, intend to do the rest when I can afford it, but that may not be for a while yet. Just gotta get that lucrative new contract ...

[John Stumbles]

Slightly misleading choice of words Ed? Not 'Not to Current Standards' as in gas-speak unsafe situation classification but 'not in accordance with building regs'.

Wonder what he did about the Benchmark though? No Benchmark, no warranty, isn't it?

And another CF too - wonder what sort of flue it has? ISTR a recommendation that a liner should be replaced at the same time as the boiler unless it can be expected to last the full lifetime of the new boiler. But then with a new Potterton maybe that's not too long OK ;-)