Only reading 100V output from boiler to CH pump

[Dingers]

Hi Tony, if you are still there.

On the boiler terminal, with the live wire to the pump removed there is no output voltage between the pump live terminal and the earth when the boiler is fired up, so I think this confirms your diagnosis that there is a problem with the boiler, probably the pcb.

What still confuses me is the voltage betwen the live pump wire to the boiler (bare wire) and the earth is still 108V. The 108V is always on when the programmer is set to either CH or HW or both are on. The voltage goes off when the CH and HW are off. I think the pump must be wired to the programmer as well as diirectly to the the boiler, would that be normal? and if so would the 108V be normal?

Th CH system has worked fine since the new boiler was put in 5 years ago and still works fine with the pump running independantly but continuously from a 13 amp socket. I haven't changed any of the wiring.

 

[Dingers]

I've attached a sketch of measured voltages in my album, click on dingers

 

[Agile]

Based on your sketch there is no other connection to the pump.

I suspect you have not shown other wiring and there is a connection to the valve somehow. There should not be though.

The pump should be powered just from the boiler.

It seems the PCB pump relay has failed.

I did hope to look at one but could not quickly find an old one.

Tony

 

[Dingers]

Thanks for all the advise, it's very useful. I've arranged for the Potterton Engineer to visit on Friday at fixed price £329. Includes parts and labour and 12 month waranty on valves and pumps etc, so if they do have to replace the PCB it's probably a reasonable price. I'll ask him to check the wiring as well.

Thanks

 

[Agile]

British Gas do a fixed price repair for about £180 which would be cheaper. Looking back I am sorry that we may not have pointed that out to you.

I am surprised that Potty have become so expensive!

May pay to check with BG and cancel Potty if you can?

Tony