What boiler?

Brie

@macman - thanks for your assistance. really appreciated.

doodling

Hi,

I would add that a 28kW boiler will easily keep a reasonable number of radiators hot no matter what the outside ambient temperature is - it is quite rare that houses have 28kW of radiator capacity installed.

If a house isn’t warming ul then usually it is because the radiators aren't big enough; boilers (especially combis which need to be big enough for the instant hot water heating) tend to be much bigger than they need to be.

Boiler performance does not materially degrade over time (assuming serviced every 5 years or so) and it is extremely unlikely that the gas supply network cannot deliver the required pressure.

As others have said, it appears that you may have a defective expansion vessel if you are getting wide swings in pressure which eventually end up requiring you to top up the system. The pressure swings also cause the pressure relief valve to lift which can cause dirt to migrate to the seal in the valve and result in a continuous slow leak.

With respect to the radiators only getting warm, this is probably not related to the pressure problems (unless the boiler is cutting out because it has detected too high a pressure) - there are a number of possibilities:
1. You've just had a shower / bath and the boiler has been heating the hot water rather than the heating.
2. The room with the main thermostat in it is up to temperature and the heating has turned off.
3. The TRV has turned off / down the radiator you were feeling - note that cold weather will accentuate temperature differences within a room and as a result a comfortable TRV setting for a 10 degree outside ambient may be slightly too low to be comfortable for a 0 degree outside ambient.
4. The system is poorly balanced and most of the heat from the boiler is passing through only one or two radiators before returning back to the boiler.  This stops the boiler from giving its full output.  This is easy to check by feeling the temperature of the central heating pipes in / out of the boiler (be careful - they may be quite hot!) - one should be around 70C and the other around 50C - if they both feel about the same after the boiler has been running for a while then the system may be poorly balanced (you should also find that you have one or two hot radiators and the rest just warm).  Note that TRVs will hide poor balancing a lot of the time but cold weather and / or undersized radiators will tend to reveal the problem.
5. You've turned the flow temperature on the boiler down too far to adequately heat the house. In theory this shouldn't mean that the radiators don't reach the same temperature they normally reach but it may be a matter of perception brought on by the house not feeling warm enough.

Hope there is something in the above which helps.

markin

I would bet the condensate drain, or even the radiator pipes may have been freezing as its outdoors to be the course of the no/low heat problem, hard to diagnose after the fact though, is it all fully lagged? Drafty door? photos?


If the is a digital read out what is the flow temp set to? If its set for economy for the 350 days its warm it would certainly have needed a boost in -6c, say 55c to 65c+

EDIT: The manual says condensing 50c/30c heat output 25.9 KWH, So it should have been plenty of heat, if it was actually pumping around the rads.