drayton ZA5 2 port issue. Function of microswitches

[BertieC]

Ok,
My issue is that the Drayton ZA5 port on the central heating circuit does not shut off , either when the correct temp has been reached on the wall thermostat or if I manually switch the heating off from the programmer.

What actually happens is that the valve makes a very loud clanking noise (like its jammed) and it fails to shut off.
I thought this must be the valve itself sticking as opposed to the actuator, but I removed the actuator body from the valve and can turn the spindle quite freely.
What seems to be happening to me is that if the pump is running then the valve will not close properly due to the pressure from the water (its only about 2 foot from the pump), so is the sequence of events as follows ?
C/H no longer calling for heat, signal to valve to switch off, micro switch first stops pump running and then closes valve.
Its an odd one because it only happens now and then, have had the issue for last week and had to turn off power to stop it running when I am out.

It is working fine now but I know sometime soon it will stop again.

By way of a test I removed the valve body, switched the power on and set the programmer off. Even with the valve head off, the programme off, the pump was still running and when I tried to manually close it I got the clanking noise (pressure too much I guess).
I refitted the valve head and now all ok, but I know it will break soon.

So it either must be faulty microswitch not turning boiler off first, or the pump has intermittent wiring problems making it run when it should not.

The boiler by the way is an old gloworm 30ff thing, has brand new pcb but the issue with the pump/valve was before the replacement so have ruled that out.
I am guessing a new head may fix, but dont get why even with the valve head removed and the heating switched on I can still replicate the problem.

Any ideas or help most gratefully received.

 

[BertieC]

one other thing has occurred to me, the water hammer that appears to be stopping the valve from fully closing, is this normal?
What I am saying is even if the microswitch was working properly and stopping the pump and boiler from running, the H/W could be calling for heat and as such the pump would be running, causing the valve to hammer when the C/H is turned off?

perhaps I am thinking about this too much now.

 

[D_Hailsham]

Is the valve the correct way round?
Water should go in at port A (from pump/boiler) and out of Port B (to radiators).

Do you have an automatic bypass on the system?

 

[TonyW2]

Room or tank thermostat operates the valve motor to open valve. The motor also has a gear wheel that operates the microswitch to run pump.
If either sticks, then pump may continue to run.
The boiler cuts off when the contents reach cut off thermostat temp.
If pump is still running with valve closed, any hot water should travel via a by-pass circuit, or the radiator near the wall thermostat that should not have any thermosta valve.
Problem is most likely a worn gear/damaged microswitch.

 

[BertieC]

Is the valve the correct way round?
Water should go in at port A (from pump/boiler) and out of Port B (to radiators).

Do you have an automatic bypass on the system?

This I need to check, I would have assumed the valve was the right way round as has worked fine for years.
Does the lever on the side with labels A and B refer to ports then?

 

[D_Hailsham]

Does the lever on the side with labels A and B refer to ports then?

The lever is misleading; it just shows if the valve is open or closed.

If you look on the brass body (you may need a mirror), you will see it is marked A at one end, and B at the other. It's these that I was referring to.

 

[BertieC]

I have laid on my stomach for the past hour, tried taking photos, tried using a mirror but still cannot see any A or B on the brass valve body.
However I do notice that the valve for the C/H is set horizontally with the wiring plug nearest the pump.On the H/W its the other way round, the wiring plug (the inlet lead) is on the opposite side, furthest away from the pump, which indicates that they are not installed in the correct way.

 

[D_Hailsham]

Remove the actuator (that's the box part of the valve) by pressing the button on the side. The valve will be held in the closed position by a spring.
The closed port is A and the open one is B.