Pump overun

Myson Apollo wall mounted gravity fed CH system - Loud banging

Sorry to keep persisting with my noisy CH System, but I have just had a Eureka moment. After i had finished descaling the whole system I turned the central heating on to start bleeding the rads etc. After about 10 minutes the banging started as usual, but I also noted that seconds before the banging started I heard a click and the pump stopped. The question I have is - is this a faulty pump overun switch or what. If so how do I change it? If I keep switching the boiler setting between high and low the pump fires up again and the system then runs ok

Pump stopping will certainly give the symptoms you refer to, if this boiler has a pump over-run 'stat it will probably be a single pole C/O switch. If one pole has gone high resistance it will stop the pump, so check its output as necessary.

Thanks meldrew's_mate

Where am I likely to find this overun switch and how do I check it has gone high resistance (does this mean open circuit?) Why does it work ok once I get the pump going again?

Anastasia said:

Where am I likely to find this overun switch and how do I check it has gone high resistance (does this mean open circuit?) Why does it work ok once I get the pump going again?

Click to expand...

Switches of this kind are usually connected between a live connection in the boiler, switched live output from the boiler 'stat, and the pump output. IF this boiler has one (I'm talking typical, not specific) it will be in your boiler and in a position where it can sense the water temperature.

For the puroses of this thread high resistance means open circuit (as the effect is the same = stopped pump) Re-starting the pump will disperse heat from the boiler and normal operation will resume until the boiler re-heats.

Forgive my presumption, but it seems you are not familiar with testing so it's perhaps best you get in a CORGI fitter. Also, have you checked whether or not the pump is actually driven via a boiler output?