Happy New Year etc. Brexit, Daesh, Trump etc, blah blah, but more importantly my boiler is having issues.
No hot water this morning and it was evident that the boiler (a 30 year old Potterton) was off. It restarted OK and ran for a few minutes.
I changed the thermocouple but it behaves the same. In fact, if it's just the pilot that is on, then it stays on. It's only when the burners start that it shuts down after about 2-3 minutes.
Any ideas or is it time to call a man in? Ta.
I assume the pilot goes out at the same time?
It does suggest the flame isn't acting on the thermocouple when the main burner is firing or the pilot, through a change in airflow, simply goes out.
Yeah, when the burners go out (after 2-3 minutes), then so does the pilot. If I manually turn off the burner (eg. turn the CH thermostat down), then the pilot stays on.
To be honest, when the main burners are going I can't actually discern where the pilot flame is.
Is the pump running? Does it have an overheat stat that automatically resets or is it one that you have to manually reset?
Tim
The pump runs (or sounds like it). The overheat stat automatically resets.
On my long since gone Kingfisher, the pilot jet would get partially blocked resulting in a small flame. Enough to keep the thermocouple active, but the boiler lighting would blow it out. Giving it a good clean so the light was back to normal size sorted it. Happened a few times over the years.
In theory, you could see the pilot light through the 'window' - but mine was rather fogged up.
This happened to my dad's boiler. The pump wasn't pumping, as Tim hints, and the boiler was shutting down on overheat a few minutes after firing up.
Before it shuts down, feel the pipes either side of the pump. If it's pumping, they'll be much the same temperature. In my dad's case, there was a clear difference in temperature, and a replacement pump (ToolStation IIRC) fixed it.
(The 'heating engineer' dad had called couldn't find the fault. To be fair, I think that's because he was as thick as shit.)
Cheers
The pump sounds like it's running, and the temperature both sides feels about the same. The boiler only runs for a few minutes so it doesn't get very hot.
Sounds like a good theory. But... If I force the burner to start by turning the CH on, and then stop it shortly afterwards the pilot is still on. If I force the burner to start and wait until it shuts off by itself (only a couple of minutes), then the pilot is out.
I'm pretty sure it's not the thermocouple (unless I positioned the replacement in the wrong place), and I'm pretty sure it's not the pump. So anything else is likely beyond me to change safely - so time to get a man to have a look. It'd be nice if I can help him diagnose the problem though.
Mine - of similar vintage (1988) but not Potterton - suffered a similar problem a few years go and it was found (not by me) to be a faulty overheat sensor. It was simply bypassed until a new one was fitted.
So when your overheat sensor triggered it shut down the whole boiler, pilot and all? How do they work? If I disconnect it will the boiler work or stay in shutdown? I see what looks like another thermocouple lead going to the top of the boiler.
I can't remember whether thn pilot failed or not. In my case the sensor was a 1" across device fitted on the output pipe. It needed to be shorted out.
The pilot jet could still be the problem as the airflow caused by the main burner does not blow out the pilot but sucks it away from the thermocouple which will close the gas valve for both main and pilot jets. This would match your observations. My thorn boiler used to do this and jet would nearly block with hard black crud. you need to clean this off carefully without chipping the jet otherwise it gets too large and wastes gas. New yets are quite standard, just get one with the same number (bray number) specifying the jet size.
You say that the main burner and pilot both go off when the problem occurs. Are you sure that they go off at the same time? It may be difficult to see whether the pilot is on when the main burner is on. I'm wondering whether it's possible that the main burner coming on blows the pilot out but that the thermocouple stays hot enough - maybe picking up some heat from the main burner - to keep the gas on for a couple of minutes.
It would be worth cleaning the pilot jet and making sure there's a decent flame aimed at the thermocouple.
Bob, Roger, I have a man coming tomorrow am to have a look. He said it sounds like crud on the pilot. Hopefully an easy fix. I'll let you know the outcome. Thanks all.
Last time I saw a similar failure mode, it was a knackered gas valve. The test would be to stick a volt meter across the mains input on the gas valve. If its still got 240V present when it shuts down, then the valve is knackered.
Does the pilot light look to be a decent size?
Thanks John. Could you explain how the gas valve works please. I can light the pilot without mains to the boiler, and it stays lit. Is that normal?
I lit the pilot and fired up the burner. The voltage on the gas valve was 240V (white and blue wire if there is a standard). In failure mode, the burner and pilot go out and the voltage on the valve remains at 240V.
Would that not to be expected though? The CH controller is still asking for heat, but for whatever reason the boiler has shut off as it thinks there is no flame. Even after a failure when the pilot and burner are out, when the CH controller asks for heat the valve gets 240V, and when it's not asking for heat the valve gets 0V.
New gas valve then?
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