Recently our boiler has started cutting out after 30 minutes or so. I'm suspecting its because the water isn't moving around the system but I haven't been able to check the pump is working ok. I've tried opening the centre screw in the pump so I can see if the pump is moving but the water just keeps coming out so I can only open the screw a turn or so. Any ideas what can the problem be?
Should mention that our living room rad does heat up quite well until the boiler cuts out so I know the water is getting that far.
Pump and valves were replaced about 6 months ago.