Heating on as per timer but pump shuts off after an hour ??

Hi guys, if somebody could offer any advice on my issue it'd be really appreciated.

I've an old 'Glow-worm Fuelsaver' balanced flue boiler, with Drayton timer & stat. The timer correctly switches the heating on and radiators come on but only for around an hour then the pump goes off whilst the boiler is still correctly firing, after this I've noticed the pump comes on for brief periods of about 30secs or so then goes off again.
The overall room temperature is still low so pump is not being switched off by the room stat.
I've also double checked the room stat with a circuit tester and it correctly powers on and off when the dial is rotated.
Tested the feed to the pump with the circuit tester and it confirms that the power to it is switching off after about an hour so the pump is fine.

I'm guessing that it's either the controller or circuit board on the boiler unit, do the symptoms point to either of these or I have I missed something ?

Thanks in advance for any advice

Chris

It could be the pump sticking when it gets hot.

algas said:

It could be the pump sticking when it gets hot.

Click to expand...

Algas, did think that myself at first but i sat with a circuit tester on the feed next to the pump and it definitely powered off which stopped it, this is the only thing that's pointing me towards a 'control' issue

Could a dodgy 3way valve cause the symptoms above ??

The pump seems to be wired into the boiler thermostat on some of these models, presumably so that even when demand is removed it will overrun while the water temp is still high.

I would take a look at the voltages around that temp control.

Bit more investigation tonight, opened up the 3-port motorised valve/actuator and the motor itself was red hot to touch, is this correct ?? Or have I found the problem ?