Combi boiler - CH going cold after a while

Le_Kirk

The pump over run will be on as long as the temperature of the water in the return pipe is above a set point (that is normally held within the boiler PCB). The temperature is detected by a thermocouple clipped to the pipe and wired to the PCB. Make sure the thermocouple is clipped firmly on the pipe. Also check that the thermocouple is connected properly to the PCB. I had this issue a few weeks ago when the little plug on the end of the thermocouple wires was pulled slightly off the pins on the PCB and the system was open circuit and assuming it was high temperature.

Should go without saying that you do these checks only if you are competent and with power off.

The red light with a circle is probably just the Power On light, particularly if the boiler works. If it was a fault light, RED usually means lock-out and you would have to carry out a reset or power cycle.