Cylinder thermostat wiring advice

justinhow · 1 Apr 2011

I have a Bosch Worcester System Boiler with two motorised valves for the water and heating zones.
Currently my boiler pump runs all the time when the programmer turns on the hot water zone even when the water is hot enough. This is because the motorised valve switch makes the circuit for the Switched Live back to the boiler and the boiler pump runs all the time with the Switched Live high.

I was thinking whether I can put a Cylinder thermostat in series with the Switched Live so that the Live is dropped to zero when the hot water is up to temp? Is this ok or should it not switch mains voltage. If not how else could I do it? Help greatfully received.

ironman1 · 1 Apr 2011

If system controls are wired correctly there would be no need for what you propose................................when both heating/HW circuits are satisfied switched live feed to boiler is removed , you may have issues elsewhere.

justinhow · 1 Apr 2011

The pump goes off when the heating is up to temp as I have a programmable Heatmiser Thermostat which turns that zone off (and therefore the associated valve) when up to temp.

However the zone for the hot water controls the motorised valve which sends the SL high to the boiler. Nothing is in the circuit to say to switch this low when the hot water is up to temperature. The boiler will not fire because its own thermostat can detect the water is hot enough but as long as it gets the SL high then it will pump (The Bosch Worcester engineer confirmed this is how it operates). Obviously it will turn off when the Programmer turns off the Hot Water zone, but I am talking about when the zone is on, but the hot water is up to temperature.

I can't see how else this should operate unless I put a cylinder thermostat in the SL hot water wire to turn of the boiler.

Am I wrong in any of this?

45yearsagasman · 1 Apr 2011

Are you saying that you do NOT have a cylinder stat fitted at the moment?
If you do have one fitted then for sure the fault is with the hw motorised valve if the wiring is as per standard SPlan.

justinhow · 1 Apr 2011

As far as this post is concerned assume I have no thermostat fitted.

I would like to know should/can it be wired in series to the Hot Water valve SL return?

If not how else should it be wired in - are there any diagrams anywhere?

justinhow · 1 Apr 2011

I have just looked at a wiring diagram on the internet that suggests it should lead be wired to the Hot Water Motorised valve (Sunvic) and in affect turn the valve off when hot water temp is reached?

Is this correct?

This may indeed be how it is currently wired, however as the micro switch in the Sunvic has failed the SL is pemanently high. I have ordered a replacement actuator.

Just trying to get my head around how it all works so I am slightly less reliant upon the plumbers and their availability (with me having to take a day of work each time they come out).

D_Hailsham · 1 Apr 2011

justinhow said:
I have just looked at a wiring diagram on the internet that suggests it should lead be wired to the Hot Water Motorised valve (Sunvic) and in affect turn the valve off when hot water temp is reached? Is this correct?

Yes. The cylinder thermostat controls the supply of power to the valve motor. The position of the valve (open/closed) controls the microswitch.

as the micro switch in the Sunvic has failed the SL is pemanently high.

That happens because one side of the microswitch (normally the grey wire) is connected to a permanent 240V supply.

You can check by disconnecting the grey wire when the boiler is supposed to be off.

45yearsagasman · 1 Apr 2011

Its not uncommon for those actuators to fail in this way.As suggested above check the switch in the valve for correct switching.

justinhow · 1 Apr 2011

I have already proved that the Sunvic Actuator is faulty as I had a multimeter on it last night and the SL stayed at 240v whatever the zone setting was.

Just wait for new one to arrive and will see if all startes to work as it should.

Thanks for help.

diynot

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Cylinder thermostat wiring advice

ironman1

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