CH OK, no HW: pump doesn't come on when manually open HW vlv

[amaccormack]

So, back from holiday and as always the heating system is acting up after the summer break...

Central heating is fine: all radiators heat up, so its not a gas boiler problem. Hot water is not getting hot, so using the backup electrical immersion

Now, the boiler feed goes through the pump then splits with a electrically controlled valve on both the heating and the HW. Turn on the heating, pump starts, boiler starts and valve to heating opens. Turn on HW and nothing happens at all - the pump isn't even trying to do anything. If I manually open the valve with its override, still nothing from the pump.

If I open the HW valve manually and turn on the heating so that the pump operates, then the water starts to heat up. Simply from my plumbing-ignorant electrical engineer's view of the system it looks to me that the thermostat on the HW tank must be open-circuit for some reason, even though the water is cold... does that seem a reasonable guess? Is there anything else I can do to diagnose the problem?

 

[gas4you]

Check if there is power on the brown wire to the HW zone valve.

Sounds like the actuator is gone to me. Opening on manual only opens the valve, it does not operate the microswitch to tell the boiler to come on.

Brown is live to motor, grey is live to mirco switch, orange is live out from microswitch to tell the boiler etc to come on.

 

[amaccormack]

Thanks for the reply. Yeah, I checked the continuity on the HW tank thermostat and it is closed circuit when cold, so its not that. If I manually open the valve, the pump and boiler comes on for a very short while. This sounds to me like the symptoms described here: http://www.grahamvideos.co.uk/honeywellzonevalve

So, do I just need to pop into B&Q and get a 17 quid motor replacement? http://www.diy.com/diy/jsp/bq/nav/nav.jsp?isSearch=true&fh_search=Synchron+&selected=products
Would it be cheaper in a plumber supplies?

 

[gas4you]

I thought they were about £10 + VAT. I never fit them, just change the complete head, but if you can prove it is just that then go for it.

The entire head is only abot £26.