Honeywell CM 907 Thermostat

[MartinHampshire]

I had a Worcester engineer come to assess why the pump was continually running. I could hear it during the night and this has been the case for a long time possibly since installation.
He advised there was nothing wrong with the boiler but identified there was a short creating a small voltage from the thermostat.
I was just going to change the thermostat but noticed that when I removed the thermostat from the backing plate its still running. Would you expect that?
the only way i have found to stop the pump is to switch it off at the fuse box.

 

[stem]

If the pump is an integral part of the boiler, such as a system boiler, or combi boiler for example (you don't say what type of Worcester boiler you have) the boiler will control the pump. With a combi for example, the pump has to run when a tap is turned on even if the heating is off.

In such circumstances, the room thermostat switches the boiler 'on' when heating is required but the boiler looks after the pump control. So, if the boiler is running when it shouldn't be there could be a fault with the thermostat, but if the boiler isn't running but the pump is, then it will likely be the boiler that isn't controlling the pump properly.

On the other hand, some boilers have an external pump that is not controlled by the boiler in which case the boiler will not be at fault.

Basically, it all depends on the type of system you have.

 

[Dan Robinson]

Depending on the specific boiler - it is probably the pump being faulty.