CH Help - Rads Go Off When Water Goes Off

[Bread]

Hi, I'm after a bit of help please.

We are having a bit of a problem with our heating. The rads don't stay on long enough to for the house to reach the temp set by the thermostat (20 degrees). It seems like that once the water reaches it's desired temp it, the heating is turning off as well. So the rads stay warm for a little while but then go cold again. They only seem to come back on once the water has cooled or perhaps a bath is run and so the boiler comes on to reheat the water.

I've changed the thermostat (old) and also the programmer (broke) but still the same problem exists. From doing a little research on the forum it seems that it could be a problem with the 3 port valve? The current one is a honeywell v4073a, this is the original one from when the house was built 20 years ago. When in use the valve/actuator does get warm/hot to the touch. Could it be the motor has packed in or is it possibly the whole valve that needs replacing?

Am i on the right lines or could there be another possible solution?

Thanks

 

[clf-gas]

Your on the exact right line

Possible its just the sincron motor, or you could change the head completely.

 

[Bread]

Cheers for the reply.

I think i'll have a crack at the motor first as it's the cheaper option.

 

[MANDATE]

Sounds as though it motors to mid position cause for a limited time you get CH and HW, but when HW is satisfied it should go to CH only position.
You could check to see if it takes up the correct position and if it does, then the problem will most likely be a faulty micro switch.

 

[Bread]

From what i've seen the switch stays on auto all the time. At no time does it move. Saying that it did move to the mid position when the power was cut.

 

[MANDATE]

Can't move to mid position when power is cut.
When all power is cut valve drops back to HW position, regardless where it was ie CH or CH/HW.
HW only ......no power to valve
Room stat provides power to white wire to move valve to mid point.
Programmer HW OFF/ cylinder stat provides power to grey wire to move valve on to CH position.
With no power on grey and white, spring unwinds motor to resr position(HW)