pilot lit - main burner causing prob

[stujm]

My pilot light will stay lit over night with the heating off.
When I turn it on in the morning the main burner will ignite but only burn for about 5 minutes - the thermostat is is set to 30 degrees.
The main burner will stay off for a few minutes then start again - but after two or three cycles of this behaviour the boiler will make a loud click and will stop. The pilot will go out also.
Sometimes on starting the heating with the pilot lit the burner fails to ignite and (click noise) and then the pilot goes out.

Is this the thermocouple? Or is this something to do with the thermostat which the boiler seems to pay no attention to?

Many Thanks
Stuart

[htg engineer]

Boiler make and model, it seems that the boiler is overheating or the overheat stat is faulty, check the pump is running.

htg