I'm a registered gas engineer, got called out to the above because of no C/H. The DHW side of things is fine. The system is pressurised to just over 1 bar. When trying to start in C/H mode the pump runs for about a minute then stops, the fan doesn't come on. There is no fault code displayed. The operation of the of the divertor valve is OK. The C/H thermistor had a resistance of 11000 ohms when cold which I thought was OK but replaced it with a new one (12500 ohms when cold) just in case, but this didn't make any difference. If I disconnect the wires from the thermistor I get an F2 fault - Thermistor failure again proving the thermistor is OK. The flow switch appears to be OK in that if I take it off the divertor valve I get an F0 fault telling me there is no flow. Is this proof enough that the PCB is at fault or am I missing something along the way?