Ideal combi boiler blowing mains fuse

[ianianian]

I have an Ideal Response 80 combi boiler that has stopped working.
The hot water was working fine, but the problems started when I first turned on the central heating.

The boiler started to heat up, but after a few moments it started to vent from the automatic air vent, so I turned it off immediately and let it cool down. A short while later I tried to run the hot tap, but there was no hot water. I started investigating and found that the 2amp mains fuse had blown (on PCB40). I replaced the fuse and tried the tap again. This time I had hot water, but as soon as I turned the tap off, the fuse blew again.

I followed the fault finding tree in the user manual which suggested that the pump may be at fault. I checked the pump for shorts between L/N and L/E but found none, however if I disconnect the pump from the PCB I am able to turn the hot tap on and off without the fuse blowing.

I have not tried to turn the CH back on at all.

I have had an engineer out to look at the boiler, but he was unable to diagnose the problem. Does anyone have any suggestions?

 

[mickyg]

sounds like it could be the pump faulty. Why couldn't the "engineer" diagnose the fault? Did he have a multimeter?

 

[ianianian]

Yes the engineer checked the pump - it was reading about 160 ohms. I had already purchased a repacement pump in anticipation of that being the fault. The replacement pump reads 170 ohms and the engineer said that was a normal reading for the pump.

Thanks,

Ian

 

[ianianian]

Any ideas why the fuse would blow when turning the HW off, rather than when it is turned on? Surely the pump would be under highest load when it starts up?

 

[petit_pablo]

Sounds like the pump to me.