Motorized Valve Wiring

[asalcedo]

I have installed two new boilers at home.

The company that did it left the wiring of the boilers to the controls unfinished and certainly not as before. I am trying to make them do it but don't know yet if it will take long.

I am trying to do it myself.

I have a typical, I would say, Honeywell S configuration. Five motorized Honeywell valves, one for each four floors in the house for central heating plus one for the hot water.

The valves are controlled by room thermostats and the one for the hot water tank by a cylinder thermostat.

The thermostats are fed by a timer with five channels.

My problem is that I do not seem to find the switched life returning from the valves so that I can connect the boilers to it.

I have read that the orange cables from the valves should be connected to the boiler.

However, although in my case the orange cables are indeed connected together to a common end point, there is never life there. Even when some of the valves are open.

Where do I find the switched life coming from the central heating valves when they are open (timer on and thermostat asking for heat)?

I would expect that switched life to be at the common terminal of the orange cables. The switched life being supplied by the grey cable that is connected to the orange when the valve is open.

In my case, though, the grey cables are not connected to life.

I have thought of connecting the grey cables to life with a piece of cable, but I have noticed that there is a 234 V diferential between the life and the grey cable, if I connect them there can be a short.

[dennis]

live from timer to thermostat.. switched live from thermostat to valve motor.

Permanent live to switch on each valve.. switched live from all valve switches to boiler on.

It sounds like you are missing the permanent live.

[Roger Mills]

You have an S-Plan-Plus system (more than 2 zones). For a general wiring diagram, see the S-Plan section of

It's easy to see how to add additional zones to the two zones shown.

Basically, you need to common the grey wires from all the valves and connect them to a permanent live feed.

Of course there's a 230v difference at the moment because one is live and and the other is floating at near earth potential. But when you connect them, the grey wires will also be at 230v - with no short.

[The fact that you *thought* that was a problem suggests that maybe you shouldn't be attempting this yourself.]

[Graham.]

And it's *live* not life.

[John Rumm]

I think the bit of info you are missing is that the orange wire is usually on one side of a microswitch that is closed when the valve operates. You also need to connect something to the other side of the switch (like a permanent live) if you want mains volts out from it when closed.

[asalcedo]

Thank you for all your comments, that are very precise.

Yes, I was missing the permanent live connected to all grey cables.

But if it was working before with the old boilers and it was not working now, it can only mean that the electrician that installed the new boilers disconnected that permanent live to the grey cables. Why would he do that? The fact that I cannot understand why he would do it made me think long and hard if I was missing something.

Anyway, I connected the grey cables to permanent live and all is working fine now, thanks.

I put a 1A fuse in series with the new cable just to be safe.

Concerning the 230V differential, if the terminals of the grey cables were fully isolated it should not be at or near earth potential and then it should not read 230V but 0. If the grey cables were connected to neutral, then connecting them to live would create a short. So, I still think that my precaution was appropriate, am I wrong?

[Roger Mills]

If the grey cables were connected to neutral then you would indeed get a short if you also connected them to live! However, I presumed that you could see that they were not *directly* connected to anything. If you were measuring between live and the grey wires while there was a demand in at least one zone, one or more valves would be open and its/their microswitches would be closed - thus connecting grey to orange. Since orange is connected to the boiler, it would be held at earth potential via the relatively high impedance of the boiler control circuits. What you actually measured would depend, to some extent, on the impedance of the voltmeter being used. What I was respectfully suggesting is that you really need to have a thorough understanding of what is going on, and an ability to interpret what your meter is telling you, before having the confidence to make further connections.