I have a Potterton Prima boiler, that I suspect the overtemp thermostat is cutting out early. It has always done this.
What temp should it be cutting out at?
Or in other words, what should the maximum hot output temperature be? If the boiler thermostat is turned up beyond about 2 of 5, the overtemp thermostat will eventually trip (hours to days).
First check the main thermostat. Put a pipe thermostat (or IR non-contact type) on the flow pipe and ensure that the water isn't above 85C before suspecting the overheat one. Assuming it really does cut out below 85C, then the overheat thermostat does sound like it is knackered.
Christian.
Does your boiler have a pump over-run stat - designed to enable the pump to keep running for a while after the boiler has stopped firing, in order to dissipate the residual heat? If so, is your pump correctly wired up to make use of this? If so, is there *always* somewhere for the water to go? If you have an S-plan system (with separate zone valves rather than a mid-position valve) or if all your rads have TRVs, you must have a by-pass circuit. Have you got one?
If your room stat tells your boiler to stop firing, and if the pump stops at the same time, the residual heat in the metal of the heat exchanger can easily heat the static water to a high enough temperature to trip the cutout.
I believe so. Now that I know a reasonable number, I'll go and check the temperature of the water output, to see if it ever gets too hot.
Not all the radiators have TRVs.
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