Link out the thermostat at the boiler, and run the heating. This will test the rest of the system.
Not familiar with the powermax 155 but I believe the pump does not run for hot water ? can you confirm this ?
If so then it's probably the pump tripping the electrics as the pump will come on when the thermostat calls for heat.
It should have a fault finding guide in the back, and also a wiring diagram. Try following the fault finding guide, also look at the wiring diagram. If you can find where the connections are for the room thermostat on the boiler, removing the wires and adding a link will bring the boiler on.
Does the water work ok ? if so PCB, gas valve, fan (if it has one) etc will probably all be ok.
If the electric still trips with the stat linked out, them i'm thinking it'll probably be the pump at fault.
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