DIY Doctor UK DIY Forums

Hi all.

All of a sudden we have no hot water but nice 'n warm radiators throughout the house. Timer hasn't been fiddled with by the kids, the boiler seems to want to fire up on 'OVER RIDE' for the HW but promptly shuts down again. Hot water tank stone cold, BUT when I force override, top feed to the tank copper coil gets red hot very quickly but the bottom coil exit pipe (the one attached to the motorised valve) is cold.

Air lock???
Busted motorised valve???

I fear it may be a while to get a plumber out promptly for this (based on past experience) so as its nearly the weekend I thought I'd just ask you guys for any hints advice suggestions and likelihood of being able to tackle it myself.

The valve could be faulty, but it could just as easily be the tank thermostat (have you tied turning it up to see if it clicks?), the wiring or even the programmer.

You can force the valve open manually by sliding the little lever on the side of the valve to the end of its travel and hooking it in the slot to prevent it returning to the closed position.

Thank you plumbbob!

The thermostat clicks, and not only that, I can hear the valve motor shutting the valve when I turn the stat down (doesnt make a sound when I turn the stat up - is this significant?).

Setting the valve manually via lever and the boiler fires up but only for a few mins.

had the timer set to CH off and HW on continuous since last night and we have now have warm but not hot water!

I would suspect the valve, if you have isolators both sides these are very easy to replace, if not it's a drain down or possibly freeze.
If the rads get warm when the ch is not calling, but the hw is, then it is the valve.

Operating the valve manually opens both ports so both hot water and heating should be on!

If the water is still refusing to circulate the cylinder coil, you need to cross off other possibilities.

Has the lockshield valve in the coil circuit blocked or been shut off??? Is is possible the circuit is airlocked. This is a common fault but usually only after a drain down.