Hot water not calling for heat

[sadgrandad]

I discovered that my water wasn't heating when I took a shower and froze.
Not a huge problem a.t.m. as I can use the immersion. Boiler fires up fine when CH prog selected.
I thought it would be a zone valve, confirmed in FAQ, but I've got 2 (Honeywell V4043H1056) - 1 close to the h/w cylinder and one further away.
I switched them both to the manual position & still h/w not calling for heat.
When I turn the CH on, the valve furthest from the cylinder moves its switch but the one near the cylinder doesn't do anything. Is this one f***ed?
If so, do I just remove the single screw in the galvanised cover to access the workings?
Thanks,
Sad

 

[Softus]

I switched them both to the manual position & still h/w not calling for heat.

You can't make those MZVs call for heat using the manual lever - it just opens the valve but not far enough to close the microswitch.

When I turn the CH on, the valve furthest from the cylinder moves its switch but the one near the cylinder doesn't do anything. Is this one f***ed?

Not necessarily. It will move only if you select DHW at the programmer AND the cylinder stat contacts are closed. There are also other reasons/faults than match the symptoms you describe.

If so, do I just remove the single screw in the galvanised cover to access the workings?

I wouldn't go there just yet. First, determine whether or not power is reaching the cylinder stat and, if so, whether it's switching through to the MZV.

 

[sadgrandad]

Thanks,
I'll see what I can discover.

 

[gas4you]

You should have 2 lives into the zone valve. Grey and brown. Brown is what makes motor turn, grey is permanent live to microswitch, which when activated sends live back down orange to tell boiler and pump to fire. Could be just synchron motor gone or change entire head. Could possibly be the cyl stat faulty. You need to test all with multimeter if you are comfortablw with live 240V electrics.

As a stop gap set hw valve to manual on with lever and turn ch on. this will /should heat hot water but without any temp control over it so don't let children run hot tap until you have checked it!

 

[sadgrandad]

Thanks Dave and Softus,

The programmer is calling the cylinder stat and the cylinder stat is giving power to the brown ZV live - nothing happens. When I operate the ZV micro-switch manually pump comes on and boiler fires up.

Is this likely to the motorised bit or the whole head that needs replacement?

Thanks again,

Rod

 

[Softus]

Motor. You can replace just that component if you're careful and averagely competent.

 

[sadgrandad]

Motor. You can replace just that component if you're careful and averagely competent.

I must be careful and averagely competent, then.

All up and running. Thanks again for input - I'll be back! (Next time I have a problem)

Rod