Can you help confirm a zone valve fault?

Hello all,

Im experiencing a problem with my central heating/hot water and i wonder if you can help me. Ive spent a few days searching in this forum, gathering info and testing etc but i need a bit of help now please, especially as cold weather is on the way this week.

It seems a common enough fault:

My central heating will not work unless the hot water is on. I have eliminated a faulty room thermostat, first by replacing it. This didnt solve the problem and i can confirm it is getting power and shows continuity when the thermostat contacts are closed.

Further searching on here revealed its most probably a motorised zone valve/diverter fault. I have found the system has 2 zone valves instead of a 3 port diverter. I have set both zone valves manually with the lever on each to the "manual open" position but the fault still persists.

I have identified that the HW zone valve appears to function correctly: the lever, when set to "man open" will automatically swing back (when released from the locked posistion) when the HW is switched off. There is also mechanical resistance to the lever and a whirr as the valve/motor moves.

The CH zone valve has a "freely" moving lever. There is no mechanical resistance when moving it to the "man open" position. It will also not return to the "auto" position on its own. There is no noise/audible whirring of anything mechanical moving.

My question is:

Does the the CH zone valve definitely sound kaput and is it serviceable? Or is it a replacement job?

I have read on here that some zone valves (depending on manufacturer it seems) can be dismantled. Is this generally the case or are most sealed?

My ZV has a screw that seems to release the cover, but due to its location i cant get a screwdriver on it. So im wondering whether to remove it entirely anyway and dismantle it. However, if they are generally unserviceable i may as well just replace it if it has to come off anyway.

The boiler is an older unit, a Potterton Netaheat, fitted mid '80's and has given no other trouble. Any advice/tips etc would be very much appreciated. Many thanks,

Mark

sounds like the valve is faulty....you will have to do whatever you can do to get the cover off to repair it otherwise you will be renewing the whole valve.

please make sure you have safely isolated the electrics to the central heating before you go digging about in there

who is the manufacturer of the valve?

Kinky John said:

My ZV has a screw that seems to release the cover, but due to its location i cant get a screwdriver on it.

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If the valve is of the type you can replace the syncron motor ,if you cant get the top off the head I hold little hope of replacing thre motor in situ. What make of valve is it .

Softus said:

Kinky John said:

My ZV has a screw that seems to release the cover, but due to its location i cant get a screwdriver on it.

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If it's a Honeywell valve, they need a small Torx driver.

oilman said:

If it's a Honeywell valve, they need a small Torx driver.

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Really? To get the lid off? When did they start doing that?

Be aware that the manual lever does NOT bring on the switch to start the boiler.

You can use a hex screwdriver bit in places with only 25 mm access with an adjustable spanner to turn it.

Apart from S-D boilers and the identical Glow-Worm boilers I dont remember seeing torx ® screws on Honeywell ZVs.

Tony

The screw to remove the head cover has been torx for years but it has a slot as well not to rule out plumbers.

But it's an 'effin thin slot.

oilman said:

But it's an 'effin thin slot.

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You're quite right, of course. I don't know how I'd failed to notice, but I've just checked my stock and all four are Torx with a thin slot.

Most of the covers I see are loose or off completely.

I do agree that on closer inspection they are of course Torx ®.

Softus please note that Torx is a registered trade mark and when quoted should always have the "®" added ( as you always advocate total correctness! )

Tony

Agile said:

...and when quoted should always have the "®" added...

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Oh p*ss off Agile - you couldn't even get the capital T in the right place, nor could you remember the screws being there, viz:

Apart from S-D boilers and the identical Glow-Worm boilers I dont remember seeing torx ® screws on Honeywell ZVs.

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It's a Torx T10, as are the two screws which hold the head to the body of the valve. I thought everybody knew that

Kinky JOhn your CH valve is stuck partially open. If you loosen the two fixing screws about 1 turn, it'll probably unjam and work for years.
If you're unlucky you need to replace the whole valve because the spoindle's seized.