I have an oldish gas boiler - Potterton Netaheat Profile - which provides both hot water and serves room radiators. Over the years this has performed pretty well perfectly. Occasionally, no more than once or twice a year, the boiler fails to turn on and the safety cut out is applied. Flicking the safety toggle back on, the system fires up again straight away.

This happened last night - temperature about minus 2degC - and house temp fell to 12degC. Since refiring the boiler is working away quite happily!

Any thoughts or advice please.

Tony Edwards, November 2010

Thanks you two guys for that advice. I have turned boiler thermostat to 3.5 and that seems to have done the trick - touch wood. Re central heating being sludged up, is this an easy matter to deal with, ie for someone who only has passing understanding of plumbing. I have drained radiators individually before but never an entire system. Thoughts would be appreciated.

Tony Edwards 30/11/10

Tony Edwards, December 2010

This boiler has a pump overrun thermostat in it so when the timer turns off the pump should run on for 5mins to get rid of the heat in the heat exchanger...or your central heating is starting to get sludged up and the boiler is struggling circulate the heat...like the other answer turn your boiler stat down a tad...

Gary, November 2010

My Potterton Profile 100e failed in just the same way on Wednesday night - the overheat cut out had tripped.

I reasoned - with no qualification or experience to support my reasoning - that the boiler was working overtime to cope with the rapidly falling outside temperature with more "on" time than usual. Because of this the latent heat built up more than usual and helped to push the over heat thermostat into tripping out. My solution was to turn down the boiler stat from just over 4 to 3 and a half.

The boiler then would continue to heat the water but its internal temperature would be a few degrees lower - that was my theory.

So far my theory is working - the boiler stayed on without tripping the next night.

Speeding up the pump may have the same effect - some are adjustable - moving the heated water away more quickly-just a guess.

Peccavi, November 2010