we have a Potterton Kingfisher mf boiler and it stopped working. on checking we have discovered that the pcb board keeps blowing fuses. any ideas? we have replaced the pcb board for a brand new one and replaced the fan. power is there then it blows another fuse.

lynn, January 2010

For many years I used to repair big data-centre computers and small ones too - it was a very rare thing for a wiring loom to be defective - in fact I can only remember one between 1968 and 1991and that was another engineer.

A defective loom is possible but very improbable - there's nothing moving around or vibrating in the boiler and the insulation will (should) be capable of coping with the internal heat.

Again I stress that I'm unqualified and inexperienced but if it were me I would find the connection to the Gas Valve and disconnect it and see what happens.

Do not be tempted to put a higher rated fuse on the Printed Circuit Baord.

If your house has an RCD on the distribution board / consumer unit and it's not tripping - then you do not have a short to earth in the boiler.

You do not have to continue with the same engineer.

Continuing good luck...

Peccavi, January 2010

we had an engineer comein to look last night and he couldn' tfind the fault but said the same, that something is causing the fuse to blow. He has now suggested that we replace all the wiring loom to make sure nothing has broken down within the wiring. once this is done he will be back tonight to see what he can do...so far 20 mins has cost us £40.00 but we just want heating.

lndylou, January 2010

I am an unqualified muppet so my advice is worthless...

The PCB just carries the fuse - you have proven (virtually proven) that the PCB does not have a fault so something that the PCB "feeds" as in delivers power to - is taking too much current - pump - gas valve - those sort of devices. An engineer may be your best approach. One method of diagnosis is to disconnect a suspect device and see if the boiler makes further progress - disconnecting the pump will cause the overheat cutout to operate.

Good luck...

Peccavi, January 2010