Funny noise from valve AFTER I switch hot tap off

[Mottie]

As per title, this morning as I turned off my hot water tap, I get a high pitched vibrating sound for about 10-15 seconds coming from the pressure reducing valve near to my hot water cylinder. It sounds like a spring vibrating as water goes past it but it’s only after the tap is switched off! Turning a cold tap on while it is making the noise stops the noise so its definitely water pressure related. This is the valve and you can feel it as well as hear it. Any ideas?

 

[John the plumber]

As per title, this morning as I turned off my hot water tap, I get a high pitched vibrating sound for about 10-15 seconds coming from the pressure reducing valve near to my hot water cylinder. It sounds like a spring vibrating as water goes past it but it’s only after the tap is switched off! Turning a cold tap on while it is making the noise stops the noise s its definitely water pressure related. This is the valve and you can feel it as well as hear it. Any ideas?

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Would you like my help mottie lol
Do the pipes vibrate aswell or is it only coming from prv?
It is a change in water pressure more than likely,just as you stated.
What’s you water pressure like generally? ( try reducing stopcock pressure and see if that helps)
It’s not uncommon for prv,s to be noisy especially when making a big pressure change.
How old is the prv?

 

[Mottie]

Would you like my help mottie lol
Do the pipes vibrate aswell or is it only coming from prv?
It is a change in water pressure more than likely,just as you stated.
What’s you water pressure like generally? ( try reducing stopcock pressure and see if that helps)
It’s not uncommon for prv,s to be noisy especially when making a big pressure change.
How old is the prv?

Thanks, yes. PRV is about 4 or 5 years old. It was coming from the PRV although it’s stopped doing it now! One thing I’ve noticed is that when I felt it this morning, it was very, very cold and now it’s just cold. Could it be ice particles blocking the mesh? Water pressure and flow seems no different to what it’s always been.

BTW, We may disagree on certain matters and if you ever need any advice about MOT's feel free to ask me but I still think you’re being a knob about Covid.

 

[MJN]

One thing I’ve noticed is that when I felt it this morning, it was very, very cold and now it’s just cold.

Something I've noticed round here is that early in the morning (and indeed overnight) the pressure is slightly higher than what it is during the day and I've always put this down to how many others are drawing from the network at these different times. Looking at the timestamps, if you were up early (for what is a cold January Sunday morning!) might your incoming pressure have been higher and responsible for a bit of water hammer within the PRV?

 

[Mottie]

I could understand the vibration if it was while the water is running but it only starts within a couple of seconds of turning off the hot tap and continued for around 10-15 seconds afterwards as if the hot water cylinder had released some pressure and was slow in recharging the pressure. Leaving the hot tap running for a fair while saw no drop in the water coming out of the hot tap. Oh well, it seems to have sorted itself out for now so I’ll see what happens tomorrow morning. I recorded it but I don’t know how to upload a sound file.

 

[MJN]

You could try closing the tap slowly and see if that avoids it... I'm just thinking anything really that might help pinpoint the cause when considered with other observations. Is the expansion vessel charged?

 

[Mottie]

You could try closing the tap slowly and see if that avoids it....Is the expansion vessel charged?

I think so. After the hot water has been heated, the first opening of a hot tap anywhere in the house results in a 3-5 second burst before it calms down which I am assuming is the expansion vessel discharging. It’s done that from when the system was converted to unvented around 4.5 years ago. Closing the tap slowly made no difference this morning.

 

[MJN]

I think so. After the hot water has been heated, the first opening of a hot tap anywhere in the house results in a 3-5 second burst before it calms down which I am assuming is the expansion vessel discharging.

That to me would (I think?) suggest the vessel isn't charged and the burst you're seeing is a result of the high pressure being released from the pipework and cylinder. The purpose of the vessel is to prevent this pressure increase (by expanding the balloon inside) from happening but if it's lost its charge (air) it can't do that.

 

[Mottie]

That to me would (I think?) suggest the vessel isn't charged and the burst you're seeing is a result of the high pressure being released from the pipework and cylinder. The purpose of the vessel is to prevent this pressure increase (by expanding the balloon inside) from happening but if it's lost its charge (air) it can't do that.

I always understood it that the initial burst was the balloon and spring inside the vessel discharging the pressure back into the hot water pipes. Surely it must do that?

 

[Madrab]

Where is the EV, is it on the flow out of the cylinder or branched off of the combination valve? Doesn't look like it's from the valve.

The vibration will probably be the PRV itself. As the spring equalises the pressure and disc moves then it may not be moving smoothly, especially if the water is so cold and the valve has probably contracted a little and is a little tight.

 

[Mottie]

Where is the EV, is it on the flow out of the cylinder or branched off of the combination valve? Doesn't look like it's from the valve.

This is the pipe that leads to the EV. It’s at the top of the Airing cupboard about a metres run from the PRV. Cold water comes down into the valve and out the bottom into the cylinder. The 15 mm pipe goes to the tundish.

 

[MJN]

I always understood it that the initial burst was the balloon and spring inside the vessel discharging the pressure back into the hot water pipes. Surely it must do that?

I know what you mean, and I'm struggling to counter the explanation. I do believe the vessel is meant to absorb and release the additional pressure in a way that keeps the net pressure the same - you shouldn't be seeing its effect. Its like you letting people in and out of a room via the front door and there's someone at the back door letting people out and in to keep the pressure the same. You shouldn't notice this at the front.

More to the point though, and terrible analogies aside, I do know that every couple of years I too find the first hot water draw of the day comes through higher pressure for a few seconds. I always know this means the vessel has lost its charge so I recharge it and the issues immediately goes away. Worth a check.

 

[Madrab]

Ah ok, thought that would have been the balanced cold supply from the valve.

The symptoms you get with the burst of water is sometimes attributed to an EV that's on the HW supply after the cylinder and it gets a burst higher pressure from the EV hot water expansion, as you mention. The other case is sometimes when the PRV itself isn't controlling the pressure as closely as it should and the downstream side ends up slightly over pressurised.

A way to test that would be to get a gauge onto the cold supply after the valve (maybe after the cylinder drain) and monitor the static and dynamic pressure swings and see what the PRV is doing. Do you have quite high mains pressure?

Has the valve/unvented been regularly serviced?

 

[Mottie]

Do you have quite high mains pressure?

Has the valve/unvented been regularly serviced?

As far as I know we do have fairly high mains pressure. It was last looked at when our boiler was serviced around August/September last year. Think he took a filter out and cleaned it but it didn’t take very long so I don’t know about 'serviced'. Pretty sure he didn’t take any pressure readings or anything.