Help-water priority valve problems

[Davenellie]

Please help, I have recently noticed that my CH system has gone mad constantly giving HW to the rads when the house is already hot.
Through a together with this it stopped heating the HW. I have discovered that the boiler is correctly responding to the thermostats but for some reason the priority valve between CH & HW does not respond. The pipe from the valve to the HW tank is hot from conduction I assume because the pipe from the tank back to the CH is cold. The pumps running and only the rads are getting heat even though the house is hot.
If I reduce the HW temp demand using the tank thermostats the pump stops and boiler clicks out, the priority valve werrs! If I then increase the HW demand using the tank thermostate again it all springs into life again. Then I seem to get movement of HW through the tank as the return pipe now gets hot almost immediately.
I think the rads are getting HW when it should be going to the tank to heat the HW, so over heating the house because the tanks not getting any!

Does this fault ring any bells with anyone. Can I change anything cheap without having to drain the system down ?

I have a danfoss valve that I have removed from the three way valve, I can move the spindle by hand so it's not ceased?

Any suggestions graitfully received?

Dave

 

[oilhead]

Replace the valve actuator. If the valve is free, then it is the actuator that is holding it in the CH position, whilst the controls are calling for hot water.

 

[Davenellie]

Thanks OILHEAD for your reply, thats the conclusion I have come to too. Through my testing, both the room and tank thermostat seen to respond getting the boiler to fire up but the water dosent get to the tank for it to achieve the required temp, instead it just blasts around the rads. turning the temp of the tank down and then back up seems to reset the valve but then it will fail the next time again. and im not sure it is actually reaching HW temp and switching off again? do you thing a simple actuator change will fix the problem. As well as the actuator attached to the valve there is also a white box on the floor its wired to. Im not sure whats this does but it looks expensive????
How much would I expect to pay for an actuator and is it a simple case of just swapping it out??

 

[ChrisR]

Check the wiring, they can be a bit wrong for years before anyone notices.
You should be able to watch the head doing its thing while it's off the valve.
HW OFF wire from the programmer/connection box is often missing.

 

[oilhead]

The white box is the junction box. You will need to open this to change the actuator. Presumably you will have a HSA3 actuator. Should cost about £50 ish plus vat