DIY Doctor UK DIY Forums

What fault would cause a combi boiler to start operating without a demand?
Could it be electrical/electronic?
The boiler is a Worcester Bosch combi 240 rsf.
This fault only occasionally happens.
The combi does not have a frost thermostat fitted.
Once the boiler operates, it cannot be stopped by switching the combi advance switch or by turning the room thermostat off.
The boiler can only be shut down at the mains switch.
The boiler appears to be firing up in the DHW mode, as the burner pressure is greater.
Also, because there isn’t an HW tap open, the radiators are heating up fast until the system shuts down after about 3-5 minutes.
The fault will occur once and then boiler goes back to normal operation.
Any replies will be gratefully received.

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