Boiler cuts out but only on coldest days

[AndyBr]

Thanks all for the responses. I had not received any new email notification of responses to the thread and so had assumed there had been no further response.

It sounds like I will have to ask my plumber to investigate but I would really need him to come out in a sustained cold spell. Even then I could struggle to replicate the problem at the precise time he is here. Even when the problem exists, an hour later the boiler can fire up again. Predicting the timing of the problem and my plumber's availability is challenging.

I am not in an area of extreme cold but even in the south of England it was -5c overnight last week and sub zero all day. Then next day 10c warmer then back to very cold again and now back to +5c over the weekend. CH behaved itself perfectly on warmer days but cut out on the cold day.

The boiler and gas meter are in a garage which is part of the house and so not that cold. No issues with any other gas appliance - hob and gas fire.

The problem I feel is some form of thermal cut out arising from extended use of the boiler on cold days. Generally when very cold the normal twice a day programme is insufficient to reach 20c (the temp drops overnight to 16c on room stat). So when between designated heating periods my wife will press the override button. That works but in fact tends to mean it will cut out sometime later. On warmer days my wife is not inclined to do this or the 20c temp is reached and the room stat turns off the CH.

I will see if I can more readily replicate the problem even on plus zero days by turning CH to continuous and raising the room stat temp to force it on for longer.

I did turn up the thermostat on the boiler - also I felt the knob turned a bit too freely so will have my plumber check that this control is working correctly.

 

[AndyBr]

As for general thermal efficiency of the house it is good but not great. Double glazed throughout. Loft insulated and boarded. Not sure exactly how thick but when done it was one standard thickness of the felt roll. The loft is very cold on cold days so it is not obvious heat is entering the loft space. There is no cavity wall insulation - had someone notice this door to door selling CWI but did not take up their offer as a bit put off by stories of ensuing damp problems. Radiators are generally original (1960s) and have not had any review done on their size but they would have been seen as fit for purpose when installed and that was pre double glazing. Boiler was installed 20 years ago - I think because the previous one was becoming costly to repair (parts). Generally the CH system has been reliable. I don't keep a record (I should). The pump has been replaced and the odd motor of the motorised valves. But that's about it. It gets serviced annually.

 

[ianmcd]

Your boiler is a very simple boiler and has no idea what the outside temperature is the problem is not with your boiler

 

[AndyBr]

True but on the coldest days the boiler has to supply heat for longer. While it could be -5c outside it will be well above zero in my garage where all the gas and CH components live (apart from programmer and room thermostat indoors). So it is not something else freezing up.

But to be sure I reckon I should be able to replicate the freezing day scenario by cranking up the room stat and turning CH to continuous.

 

[Agile]

It might be something very sensitive to temperature on the boiler or less likely on the meter.

But you may well be able to replicate the fault by opening the garage door to make the temperature go down to whatever it is outside on a cooler day.

It is odd weather with some days freezing all day and others over 10 C

Tony

 

[D_Hailsham]

The boiler and gas meter are in a garage which is part of the house and so not that cold.

Presumably the garage is not heated and has one or more uninsulated external walls, so it could get very cold. There should be a frost stat and a pipe stat in the garage. The frost stat turn the boiler on when the temperature in the garage drops below 5C and the pipe stat turns the boiler off when the water temperature reaches 25C.

 

[Steelmasons]

The frost stat turn the boiler on when the temperature in the garage drops below 5C and the pipe stat turns the boiler off when the water temperature reaches 25C.

The pipe stat signals boiler ON/OFF due to pipe stat wired in series with frost stat.

 

[ianmcd]

it is to do with your meter , regulator

 

[Stadan20]

Flux capacitor too cold ???

 

[Agile]

I am looking forward to hearing the solution when it is known.

 

[nauseous]

Our Wooster bang 24i boiler still plays up like yours. Have you tried putting a fan heater under it to warm it up. Think it's summat to do with the gas valve sticking.

 

[AndyBr]

There is a frost stat in the garage but I am not even aware of what a pipe stat is.

As Tony noted the weather has been very variable and we are due another cold spell this weekend. This past week has been more like +10c so the boiler has not had to work too hard and so no evidence of the problem. The boiler cuts out but it is because the room stat has reached 20c.

The garage is unheated but not sure how cold it gets in the on a freezing day. I will check next time - just that it never feels that cold. There will be some heat loss from the house into the garage to warm it up a bit.

If I can replicate the problem at will by running CH on continuous and raising the room stat then I can get the plumber (who is a recognised boiler engineer) to come in. Either that or we need a prolonged cold spell.

I will report the outcome.

 

[AndyBr]

So does the boiler stat actually cut out the boiler when the CH flow temperature reaches a certain level?

Does this apply to HW too? I do also have a HW cylinder stat set to about 55-60c.

I did measure the surface temp of the radiators - it varies a bit but the best one got up to 64c. Too hot to hold for more than 5 seconds. Others you could hold. I have one radiator that seems noticeably less hot than the rest but I have bled it and so that is not the reason.

Andy

 

[Agile]

Yes of course!

Once the flow temperature reaches the temperature that you set on the boiler stat it turns off. It should turn back on when the flow temperature has fallen by a few degrees and typically about five minutes later.

That is what your old boiler does. A more modern one stays on but reduces the power input. That is called modulation and is rather more efficient.

Tony

 

[AndyBr]

I rather thought it must as it is a thermostat but it seemed a bit imprecise as my dial goes from min to max and with 1-6 I think in between. Compared with my HW tank stat and CH room stat which have precise temperature settings.

Also, the dial feels a bit loose as if the rotating bit I can move has come away from the actual control spindle and so the number I see in the window may also be a false reading.

That would all make it a likely culprit. However, what is odd is that once it cuts out it takes a long time to cut back in. I recall last time it happened it was off for an hour or more. The rads had gone almost cold in that time (well only mildly warm to the touch).