Zone valve wiring

[PedroKTFC]

[Firstly, apologies if this has been asked before or is answered elsewhere. I did search around but couldn't find anything.]

The switch in one of my zone valves has started sticking again! (This seems to be a regular "feature" of my Drayton ZA5s! I end up replacing the switch every couple of years or so.)

Anyway, a consequence of this is that, when my valve sticks, the pump keeps running whether or not the programmer is on for that valve. Looking in detail at the standard S plan wiring diagram, I see that the pump (and boiler) is controlled solely by the switch in the valve (live to the pump comes direct from mains live through this switch). Can someone explain why the pump live doesn't instead come from the programmer so the pump (and boiler) at least wouldn't be running when the programmer is off? Could I rewire it in this way?

(I hope I've been clear about this.)

 

[Exedon]

I'm afraid you need to leave it as is.
The programmer switches a live to the thermostats which in turn if there is a demand motor open the valves.
If you wired programmer directly to motorised valves you would have no thermostatic control ie the boiler and pump would be permanently on whenever the programmer switched to on.

 

[CBW]

Also, once the programmer has ended the timed period, then the pump would stop, and then there would be no pump overrun, and this would cause more damage than a stuck switch.

 

[PedroKTFC]

By pump overrun, I presume you mean the pump carries on running while the valve closes. But that's only a couple of seconds or so, surely not significant? What harm could be done?

When the switch sticks, the pump runs and runs and runs against a closed valve. I'd have thought that as worse?

(I'm only a DIYer so I realise I'm speaking very naively.)

 

[oldbutnotdead]

Your boiler may or may not have pump overrun- if it does then disrupting it would be a bad idea.
If it doesn't then you could use the live from the programmer (which presumably goes to room stat and then to valve motor) to power the microswitch BUT it's not wise- you can end up with the valve latching open and giving you uncontrolled heat.
You're being very unlucky with sticky microswitches, they are rated for many millions of operations. Maybe look at Honeywell valves, or ditch the whole zone valve sketch and refit with WiFi or Bluetooth TRVs

 

[stem]

Can someone explain why the pump live doesn't instead come from the programmer so the pump (and boiler) at least wouldn't be running when the programmer is off? Could I rewire it in this way?

Yes it's quite simple. It's to keep the isolation between the hot water and heating system control.

The HW valve microswitch and the CH microswitch live outputs are connected together so both can start the boiler. So when the microswitches are closed (on) the live could feed back via one valves microswitch to the other valves microswitch, which if you had modified the wring means that it would also connected to the programmer and could keep the programmers channel live when actually the programmer had switched it off.

The result would be that when the programmer switches off the CH, it could still be getting a live on it via the HW motorised valve so the CH would stay 'on', and vice versa of course.

Sorry I didn't explain that very well, but from your first post you seem quite savvy so I hope you will understand

 

[ericmark]

I think more to do with start up, want the valve open before the boiler fires up or pump starts.

The V3 micro switch does not seem to be best option, personally I wish there were two micro switches, as I have to use a relay so pumps are independent to boiler.

I am sure one could use relays or other method, but then that may fail.

 

[DP]

What if the valve spindle is sticking. Will seem as if the microswitch is goosed.

 

[stem]

Also, once the programmer has ended the timed period, then the pump would stop, and then there would be no pump overrun

When the programmer ends, the motorised valve closes, the microswitch is released and the live to the pump is removed in this case also. Where the pump has an overrun, the pump is wired to the boiler and it's the boiler (which has a permanent live) that keeps the pump powered during the overrun.