Pcb fuse blowing

All was fine then hot water stopped then everything all fuses blown
I've replaced flow boiler, new dhw sensor and ph sensor and the relays which tested faulty
turned on and it started to work now the pcb fuse keeps blowing with a flash/pop from the board
help boiler man

Hi Darren,

The PCB fuse blowing is usually caused by failure of a pump, usually the flow boiler pump. They get wet with water from leaks on isloating valves above and usually take the board down too. I suggest replacing the boiler pump motor head and trying again.

Look carefully at the four (or possibly five) black thyristors next to the green lights on the board. Are any of them surrounded by sooty marks? If so then the the board will need replacing too, but you can follow the copper tracks on the board from the popped thyristor to see which pump it drives and THAT will be the pump that failed and caused the damage.

Cheers, Mike

Thanks Mike
i isolated the boiler pump live at the board and it did what it should apart from locking out but that would make sense because the pumps not circulating
Thanke for your help !! gonna fit new pump this evening

Yes that would make sense. The flow boiler will rapidly overheat and trip the overheat thermostat with the pump disconnected. I expect your new pump will fix it.

To protect the board from any future water in any new pump(s) I fit, I fit an extra relay, wired so the board powers the relay actuator coil instead of the pump directly. Then if the pump fails due to water ingress the board is not wrecked as a result.

Cheers, Mike

i isolated the boiler pump live at the board and it did what it should apart from locking out but that would make sense because the pumps not circulating

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