Central Heating Problem

[Drongo]

I have a Potterton Netaheat boiler and it has just been checked and given a clean bill of health by British Gas. However of the last week or so and getting more frequent. After it has fired up and been working OK for about an hour it switches itself off just leaving the fan going.

It is not the normal switch off when it has reached it's working temperatures and fires up again no problem after being left to cool down and then once heating up again repeats the cycle. I have checked the pump and that seems to be working OK. Someone suggested it may be the Honeywell Valves(2 Port I think). If that is not working correctly they suggest it may be an automatic cut off to prevent overheating.

Any suggestion would be welcome and acted upon thanks

Drongo

[Gav]

what are the settings on the controls when this happens, heating on/off water requested or not? and do the heating and water get hot as they should do?

[Ed Sirett]

I presume that the thermostat on the front has not yet been satisfied and that's why the fan is still running. However if the knob on the boiler is satisfied then the problem lies perhaps with the relay but this is fault I've not come across. Anyway you strongly suggest this is not the happening.

The next thing to check is whether the pilot is still alight if so the problem is that for some reason the flame sensor in the pilot has cooled down and cut the main gas.

If the pilot has gone out then the boiler should be trying to relight it with the sparker. Although that does not explain why the pilot went out.

I'm not sure if the Netaheat has an overheat - if it does I would expect it to kill the fan too and require manual resetting.

[Gav]

flame supervision device? could that be wanting to extract any gasses that have built up?

mmm will look on monday at the boiler fault finding book at work (as you know ed i am a trainee engineer) we need to know if it is sending water, hot water anywhere!