Faulty zone valve?

We have a couple of Boss Therm BZV22 two port zone valves controlling the DHW and central heating circuits and for the last couple of days radiators have been getting hot when the CH thermostat has not been calling for heat but the DHW has.

I've noticed there's a little play in the lever on the CH valve so I assume that that's the culprit? If it is, is it likely to be the valve itself, or the actuator?

Reply to
F
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Seems a bit odd, since without a call for heat from the room stat, the valve on the heating ought to be sat in its unpowered state with the spring holding the valve closed.

A fault in the control wiring would possibly cause what you are seeing. Rodent damage perhaps?

To diagnose, the first step would be to look at the voltage* on the supply to the valve when the DHW is calling for heat. It ought not be powered, but if it is then you know what the problem is.

If there is no unexpected demand going to the valve, then you may be able to remove the actuator head from the wet bit (I have not used that particular brand of valve). Check the spindle can be rotated easily (you may need pliers rather than finger pressure - but it should still be an easy smooth movement). If it is "sticky", adding some lubricant to the shaft and working back and forth a few times will often fix it.

Check the spring is still intact in the motor head. If the valve body is working, but the head does still not return it to the closed position, then replace the head.

  • with a multimeter, not a wet finger! Remember you are working on live mains with well earthed pipes to hang onto to make sure shocks are more likely to be fatal!
Reply to
John Rumm

Thanks. I worked my way through what you suggested and it looks like the actuator.

If I take the actuator off, the lever springs across to the 'off' position and the small amount of play is gone. Put the actuator back on, push the lever across to open the valve and when I release it it only moves part way to the closed position. Take the actuator off and the lever flicks across to closed.

Looks like new actuator head time.

Reply to
F

. . . is the wrong answer!

If the actuator returns to the closed position when off the valve but not when *on* it, it almost certainly means that the shaft in the 'wet' part of the valve is too stiff for the actuator's spring to move it back to the closed position. Unless there's something wrong with the spring (unlikely unless it's actually broken), replacing the actuator will leave you with exactly the same problem.

With the actuator off, work the shaft to and fro, and try to get a drop of thin oil into its bearings. When it moves freely, re-fit the actuator, and try again.

Reply to
Roger Mills

... is the wrong answer!

At the top of this post I said 'I've noticed there's a little play in the *lever on the CH valve*'. The lever is on the *valve*, not the actuator...

Further down I said '*If I take the actuator off, the lever springs across to the 'off' position* and the small amount of play is gone. Put the actuator back on, push the lever across to open the valve and when I release it it only moves part way to the closed position. *Take the actuator off and the lever flicks across to closed*'.

The actuator turns a brass(?) cog within its body which engages with a larger, plastic arc, with a lever attached, which moves the valve.

Reply to
F

That is different from most Honeywell valves and their copies then. Usually with those the leaver is a part of the motor / actuator assembly and not a part of the valve (which is basically just a brass tap spindle poking out of the valve body).

Rather like:

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Further down I said '*If I take the actuator off, the lever springs

Where is the spring on this valve? (usually they are in the gear assembly of the actuator - so the valve has no capability of self returning without it).

If yours is like this, then as Roger was saying, it suggests that the valve tap itself if what is stopping the mechanism getting to the closed state.

(note that the full travel of the mechanism may be slightly greater than that of the tap - hence the slight play at the closed end).

Some photos might help.

Reply to
John Rumm

OK, so your valve is apparently different from the other 99% in circulation. But I didn't know that, and reasonably assumed that "the lever on the valve" was actually the lever on the actuator, with the actuator fitted to the valve.

Again, for a more 'usual' valve, with the lever on the actuator, there

*will* be some free movement on the lever if the valve is stuck partly open - and this will disappear when the actuator is removed and can return to the closed position without the constraint of a stuck valve.

As John Rumm has asked, where *is* your return spring?

As has been demonstrated(!), I'm not familiar with your particular valve. Is there any possibility that something could have slipped on the alignment front, such that when the actuator thinks the valve is closed and when it is actually closed are not the same?

Reply to
Roger Mills

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OK, image of valve at

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the lever (1) to the right and the valve opens. Move it left, into its current position, and the valve is closed. With the actuator dismounted, as it is in the image, the springs flick the lever to the left and close the valve.

With the actuator mounted, the cog (3) engages the plastic arc (2) (to which the lever is connected) and drives it in either direction.

A second, fully assembled valve is on the left.

Reply to
F

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like you can take the head apart in stages on that one.

ok, that is not really actually actuator dismounted - your actuator appears to be in two sections - the motor in the lid, and the gearing with plastic arc bit in the base. (on "normal" valves both of them come off together)

You probably need to take that off the valve body as well, to get back to the plain brass valve and check that is moving freely.

However if the leaver move the valve to open and then it springs back to closed with it dismantled as in the picture, then it might indicate the motor itself is sticky or in some other way reluctant to move.

If you power the system up and make sure it has a call for heat, can you see the motor spin?

They normally "drive" it only open, then allow the springs to do the work to get it back to closed when the motor is unpowered.

Reply to
John Rumm

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Right, so to close the valve with the actuator attached, the return springs have to have enough urge to overcome any stiction in the valve itself *and* to rotate the motor through its reduction gears. These loads are additive. The fact that it can do one without the other doesn't *necessarily* mean that the excess resistance is coming from the other one, although it is likely. Warn teeth on the curvy bit of plastic could also be a factor.

If it were mine, I think I'd cut my losses and replace the whole thing with a Honeywell valve.

Reply to
Roger Mills

Thanks, all, for the suggestions.

I checked the actuating mechanism through, swapped the working head for the apparently faulty one and the valve functioned as it should. Either the motor wasn't driving the valve to the fully closed position, or the motor was too stiff to allow the spring to wind it back and close the valve.

So, for just over £40, I got a replacement head and the valve now works fine.

Reply to
F

Good - less hassle than changing the whole valve...

Reply to
John Rumm

That's what I thought. No drain down, no loss of inhibitor, no airlocks etc.

Reply to
F

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