Failed central heating valve?

[Graeme]

Let me start by saying that central heating systems are a black art to me. Ours is a conventional oil fired boiler supplying DHW and three traditional wet radiator zones. Two zones are working, but the third is not, and has not been used for two or possibly three years.

The zone valves are Honeywell, with a silver box on top, and having read that the protruding lever should have resistance when the heating is off, and no resistance when on, I have found the offending valve. There are three valves in total, presumably one for each zone. Just one pump, too.

I've taken the top off the silver box (one screw) and can see the actuator, but beyond that? Will tapping the actuator or the valve or anything else release it? I guess it is stuck because it hasn't been used. Can the actuator be changed without water pouring out?

[Archibald Tarquin Blenkinsopp]

If you select "images" after typing honeywell 3 port actuator into Yahoo, it should make things fairly clear.

I believe the synchronous motor holds the valve position against the stop by means of a constant "stall current" which affects the reliability of the motor. The motor is available as a seperate item.

AB

[Graeme]

In message , Archibald Tarquin Blenkinsopp writes

My valves are 2 port not 3 port, but I see what you mean. Thank you.

Thinking about it, just changing the actuator is not going to help if the valve itself has stuck. Bugger.

[ARW]

Well if you cannot open it manually then it is buggered. I assume that the programmer and stat are calling for heat.

[GB]

If you unclip the silver box (probably twist it) you will see the top of the valve. There's probably a prong sticking up. You should be able to free it up. It may well stay free until next summer. :)

You can get kits to change the innards of the valve, but it does require draining down the system.

[Graeme]

In message , ARW writes

But which part? The actuator or the valve?

Yes.

[Davey]

Let's go back to basics.

You say that you have identified the offending valve. Do you mean that it should be powered, therefore open, and so should have no resistance on the manual lever, but that it does have resistance, indicating that it is still closed?

If so, can you move the lever against the resistance, thereby opening the valve? There should be a little catch so that you can lock it in the open position. Does doing this allow hot water through the zone?

If not, why do you think this is the defective valve?

Approaching this logically should give us the answer.

Do you have a voltmeter, and the ability to use it safely? I am not being funny, I don't want you to electrocute yourself.

[ARW]

Well the simple test is to try the actuator whilst it is removed from the valve and see what happens.

TBH if after removing the actuator, the valve spindle will not turn with the help of a pair of pliers then that is your answer.

[Graeme]

In message , Davey writes

Excellent.

It does have resistance whether or not the system is calling for heat.

Yes! Why didn't I realise that? Anyway, yes, little catch locked, and rads heating. I could live with that, at least for a while. This zone heats four rads in what was our shop, attached to the side of our house. The shop is closed and the space will be my 'hobby room', so remembering to use that little catch to heat the place is acceptable if not perfect.

I'm no electrician but yes, I have a small multimeter, and can use it for fairly straightforward stuff.

[Davey]

Which indicates that the actuator is not functioning, for whatever reason, but the valve should be ok.

Good so far! Now we need to find out why the actuator is not working.

You will really need a wiring diagram at this point. I expect that the valve and wiring look something like the one shown in the 'S' Plan:

This shows that the Brown and Blue wires are the power for the valve, so IF you can get the probes for the meter to these terminals, you should see 240 V AC across them. If they are unreachable, then find where the wires go to, there will most likely be a junction box of some kind within a few feet. Try there for the same thing, and report back.

shows various Plans.

[Graham.]

Exactly right. If the lever moves back very slowly when released then the wet part of the valve is OK

If there is 240vAC across the motor when the system is calling for heat on that zone then the motor is shagged.

Does your valve have a removable head? The early ones didn't. In either case I wouldn't buy a replacement head or valve, as the synchronous motor is obtainable by itself. Generic ones should be under £10 delivered, I think I got my last ones from BES.

If there isn't 240vAC across the motor then you need to look at the thermostat and switches that are dedicated to that zone only.

[Davey]

And that's where a correct wiring diagram will make all the difference. Remember that not all setups are wired correctly, though, as I found out earlier this year.

Good luck.

[The Natural Philosopher]

Remove the silver box off teh actual valve and you should expose a shaft that should turn., Often it doesnt till some serious plier work has been done on it, by which time the actuator may have enough guts to turn it

If not its drain down and replace the lot time :-(

[The Natural Philosopher]

Ok actuator is f***ed, get a new one and fit. No need to drain

[Davey]

But he has already said that it works fine when using the manual lever to operate it, so the actuator should also be able to turn it.

[Davey]

Or there is no power getting to the actuator, in which case a new one won't work either.

[Graeme]

In message , Graham. writes

I realised that, backwards :-) When I had finished fiddling yesterday, I forgot to unlatch the little lever and realised later that the heating for that zone had come on, with the DHW. Doh.

[Roger Mills]

Not necessarily. If the wet part is stiff, the actuator may not have enough grunt to shift it - even though you can do it with the manual lever.

The OP needs to remover the actuator, see whether it moves when it's not on the valve, and make sure that the valve's spindle is free to turn.

Chances are that the actuator's motor has died, but it *could* just be a partially seized valve. If so, rotating it to and fro a few times with pliers may well free it up.

[Davey]

Before that, he needs to check that the actuator is actually getting power.

[Graeme]

In message , Graham. writes

There is a separate timer/programmer for each zone, but not thermostat. I turned the shop zone programmer off and, there being no other call for heat, the boiler stopped. What I said above is not quite true - it was the downstairs heating coming on which caused the shop heating to also come on.