Overheat thermostat tripped, can't relight pilot light

[informer]

I have a Potterton Flamingo which is nearly 18 years old. A couple of weeks ago the overheat thermostat tripped causing the flame to go out. It took many attempts to get the pilot light to relight but in the end I was successful. The boiler has been fine until today when we noticed the house was getting cold. Again the overheat thermostat has tripped but this time I can't get the pilot light to light. The pump seems to be working fine as I can feel and hear it humming. Any ideas or should I now buy a new boiler.

Out of Interest we had a radiator removed from the hall, a bedroom radiator enlarged and an additional large radiator fed from that bedroom for a garage conversion last March. This did cause the overheat thermostat to trip 24 hours later but the plumber said there was an airlock. The system has been fine since that date and has not been adjusted for temperature.

[informer]

Update.. Got the pilot light to light by holding in the pilot ingition for around 30 seconds instead of the recomended 10-15 seconds. Still need to know why the overheat thermostat has tripped twice in two weeks? Many thanks

[Andy Burns]

lack of pump-overrun or failed fan?

[informer]

Do you mean does the pump carry on running after the boiler shuts down? I guess the answer is no but the pump never overruns since we turned down the boilers thermostat years ago. As for a fan I don't think it has a fan. Can't see any mention of a fan in the handbook

[Andy Burns]

yes, some are intended to do that.

[Ed Sirett]

This is a really low tech boiler. No pump overrun and no fans. You could have a pump problem, a circulation problem or an air-lock. You might have a gas valve that is sticking in the on position? You might have a failing thermostat.

IIRC this model simply has a normally closed contact in series with the thermocouple circuit.

Your current thermocouple may be on its way out. In fact what makes you so sure the pilot dropping out is over heating? It might be any number of problems with the t/c or the pilot flame.

[John Stumbles]

Presumably because the overheat cutout has operated?!

[Ed Sirett]

There is no way in principle to tell whether the pilot went out becasue the boiler over heated or because the t/c is on the blink.

hence:

[John Stumbles]

Depends if the overheat cutout it a type that needs manually resetting. I don't know what it is on the Flamingo (or Flamin-not-go in this case :-) but there was a Texas Homecare Livin' Luxury WM 40/55 RF I used to nurse which had a manual-reset cutout in series with the thermocouple.