Y plan valve shuts with a thump.

[RigidRaider]

Greetings; I haven't been on here for a while. Hope you can advise.

Conventional open vented system with a Y plan valve just beside the boiler. When the room 'stat stops calling for heat the valve shuts off the Ch with a thump that echoes through the pipework.

Is this actually a problem?

 

[superman123]

try removing the spring

 

[D_Hailsham]

Conventional open vented system with a Y plan valve just beside the boiler. When the room 'stat stops calling for heat the valve shuts off the Ch with a thump that echoes through the pipework.

Make and model of valve?

With most makes and models, when heating is satisfied the valve will stay in the CH position (port A open), not return to HW only position. It only returns when there is a call for HW.

Is HW timed and are there wires to the valve grey wire from programmer HW OFF and from the cylinder stat SAT terminal?

 

[45yearsagasman]

try removing the spring

What good would that do on a mid pos valve?

 

[mickyg]

if its a honeywell the ball is prob loose. get a new ball and plate kit.

 

[RigidRaider]

Thanks, it's a Honeywell Sundial Y plan. There is only one cable coming to it from trunking but the HW and CH are both on timer. Actually it has thumped three times in the 45 minutes that I've been online this morning so I'm beginning to think it's when the cylinder 'stat operates, not the CH because the heating is not as unstable as that - it usually only comes on once in the morning and that's usually enough.

 

[D_Hailsham]

Thanks, it's a Honeywell Sundial Y plan. There is only one cable coming to it from trunking but the HW and CH are both on timer. Actually it has thumped three times in the 45 minutes that I've been online this morning so I'm beginning to think it's when the cylinder 'stat operates, not the CH because the heating is not as unstable as that - it usually only comes on once in the morning and that's usually enough.

The cable connected to the valve contains five wires: blue, grey, orange, white and green/yellow. It will connect into a large junction box, together with the timer and thermostats.

If the HW is called while the valve is in the heating position it will return either to mid-position (CH and HW) or to HW only. Which depends on whether the boiler is actually running for CH. A quick experiment, running through all the permutations of CH and/or HW running/not running, should enable you to pinpoint exactly when it happens.

As mickyg says, the cause could be a loose ball. If you have a modern valve with a small bump on the top of the metal box you can replace just the ball and 'O' rings - part no 272752A/U CARD. If it's an older model you have to replace the top plate as well - part no 40003918-007.

Unfortunately you have to drain down below the valve in both cases.

 

[RigidRaider]

Hello again, thought I'd bump this back up again because today I took advantage of the holiday and changed the valve.

Curious to know what could be causing the clunk I took the cover plate off the valve and exposed the ball and arm. What do I find? Diddly-squat, that's what. Apart from being a bit dirty the ball is in perfect condition and not loose on the arm so I'm at a loss to understand why it's been clunking. The only thing I would say is that the spindle on which the arm pivots is quite stiff but then I guess it's got at least one O ring inside the end plate.

So far the replacement valve is performing quietly though only on the HW as the CH hasn't come on this afternoon.

Any thoughts?