[NotGotABimmer23]

I've got a Honeywell zone valve controlling flow to part of the central heating which isn't fully closing and the upstairs rads are coming on when the hot water is on.

I've swapped the motor inside the valve over with one which I know is working but that makes no difference. Shame as that would have been an easy 11 quid fix...

I am trying to avoid buying a full new actuator but feels like that might be the solution.

It's a bit odd as electrically it's working, it opens when it should and closes when it should but it's just not fully closing. If I put it on manually by the lever then let it close it stops closing very quickly, much quicker than the other one which is working fine.

So something is preventing it from closing, I was wondering if it's the nipple from the valve that's seized but don't know how stiff this should feel, I can turn it a bit with pliers. Otherwise it's something inside the actuator gearing etc which is nackered.

Any thoughts or suggestions?

[xenon]

My central heating seems to eat those - I probably need to replace the actuator every three years. Easy to do though and you can get pattern parts for about £40. However, if the valve does not close properly by moving the actuator directly it may be that the rubber-ball part of the valve is gunked up and you'll need to replace the actual brass body which of course entails draining the system. It could also be the micro-switch that detects the mid-position and locks the motor isn't working.

If you move the brass stem there's probably only about 60 degrees of movement from A to B.

[Eddamoo]

My assumption is that there's some crud on the sealing ball or spindle that is preventing it from closing, especially if you cant get it to shut with pliers.

Seen it many times on isolating valves. One possible reason is a lack of inhibitor in the heating system.

One thing to try is tapping the spindle with a wrench or small hammer. Sometimes that can loosen the crud causing it to foul. Repeatedly tap-turn-tap-turn. Could also apply a penetrating oil.

[Pond]

As said above, chances are there is some build-up of something (probably scale or rust debris) in the valve itself, stopping it from fully closing. It only needs to let by a tiny bit to cause problems.

Normally a drain-down job to inspect/ replace the valve body unfortunately.

Worth noting aswell...if a valve isn't opening or shutting fully, it can burn actuator motors out, as it is likely the microswitch inside the actuator isn't being triggered, so causing the motor to be powered constantly. I've seen this knacker many actuator motors over the years.

[NotGotABimmer23]

Frustrating, as I would do the simple changes myself, but I'm not draining it all down. The actuator appears to work perfectly when it's not connected to the valve, closes and opens all the way, so it's got to be the brass bit hasn't it...

[NotGotABimmer23]

Originally Posted by Eddamoo

My assumption is that there's some crud on the sealing ball or spindle that is preventing it from closing, especially if you cant get it to shut with pliers.

Seen it many times on isolating valves. One possible reason is a lack of inhibitor in the heating system.

One thing to try is tapping the spindle with a wrench or small hammer. Sometimes that can loosen the crud causing it to foul. Repeatedly tap-turn-tap-turn. Could also apply a penetrating oil.

I can move it with pliers no issue, but not sure if it's fully shut or not. It seems to be able to open well past the open point on the motor, but in terms of shutting off I'm not sure.

It actually seems to move really freely, the other one which is working fine is super stiff in comparison.

[xenon]

Originally Posted by Pond

As said above, chances are there is some build-up of something (probably scale or rust debris) in the valve itself, stopping it from fully closing. It only needs to let by a tiny bit to cause problems.

Normally a drain-down job to inspect/ replace the valve body unfortunately.

Worth noting aswell...if a valve isn't opening or shutting fully, it can burn actuator motors out, as it is likely the microswitch inside the actuator isn't being triggered, so causing the motor to be powered constantly. I've seen this knacker many actuator motors over the years.

That’s not how a mid-position works. It’s a synchronous motor so is designed to be continually powered if necessary. When the motor is not powered the spring holds the valve in position A. To get to the mid-position the micro switch will switch in a diode thereby supplying DC power to the motor, locking it solid. This is how it holds the mid-position; it’s not at either end-stop but has to be held against the return spring. To get to position B the motor is simply driven against the end-stop and it can go no further but it is continually powered to hold it there. When power is removed the spring pulls the valve back to A. However the valve is designed to be quite happy at mid-position or position B continuously powered. A failed switch means it’s impossible to hold the mid-position but shouldn’t cause the motor to fail before it otherwise would have done.

[Pond]

Originally Posted by xenon

That’s not how a mid-position works. It’s a synchronous motor so is designed to be continually powered if necessary. When the motor is not powered the spring holds the valve in position A. To get to the mid-position the micro switch will switch in a diode thereby supplying DC power to the motor, locking it solid. This is how it holds the mid-position; it’s not at either end-stop but has to be held against the return spring. To get to position B the motor is simply driven against the end-stop and it can go no further but it is continually powered to hold it there. When power is removed the spring pulls the valve back to A. However the valve is designed to be quite happy at mid-position or position B continuously powered. A failed switch means it’s impossible to hold the mid-position but shouldn’t cause the motor to fail before it otherwise would have done.

The OP said it is a 'zone valve', therefore presumed it is a 2 port, not 3.

[xenon]

Originally Posted by Pond

The OP said it is a 'zone valve', therefore presumed it is a 2 port, not 3.

Ah. I had assumed a mid-position. My system doesn’t have a 2-port but I thought it worked in a similar way in that it was driven against the end-stop and then held there against the return spring by driving it on. Maybe they use a stepper motor?

Anyway, it sounds like the ball valve itself is failing to seat.

[NotGotABimmer23]

Originally Posted by xenon

Ah. I had assumed a mid-position. My system doesn’t have a 2-port but I thought it worked in a similar way in that it was driven against the end-stop and then held there against the return spring by driving it on. Maybe they use a stepper motor?

Anyway, it sounds like the ball valve itself is failing to seat.

I tried the actuator that I know works on the valve that's playing up and it seems to do the job, so I think I can get away with just changing the actuator, which I will do later today. Something must be going on with the gears in the other one and it's just not strong enough to hold the valve closed.

[AndyMD]

Do this every two years. It will add life to other components of your system too. We do ours just after a boiler service