Vibration when first opening hot tap after u/v cylinder heating cycle

[nashant]

Are the pressures equal in regards to ex and cold water - .2 bar

The main varies between 4 and 5 bar over summer, it's dropped to 3 to 4 currently. Assuming Thames Water's winter pressure level. The pressure on the combi is set to 3, this is confirmed (I think) by the pressure on the hot being 3 bar at all times apart from immediately after a heating cycle. After a heating cycle the pressure on the hot rises to 4 bar. The EV is pre-charged to 2.8.

 

[ShaunCorbs]

On a flexi ?

 

[nashant]

On a flexi ?

Nope, piped. I thought I would test the reducing valve by running the cold on a different tap that comes off the main before the combi, then opening a hot this morning. Still get the noise, didn't make a difference. So it's not the pressure on the main that's causing the problem.

 

[ShaunCorbs]

Any pictures of the unvented and pipework ?

 

[nashant]

Is it fine to have separate components instead of a combo valve? If yes, can I confirm with you the order the engineer should be installing them? I know, I shouldn't need to, I should just let them deal with it. But my experience so far has been less than stellar, so would like to be able to verify what they've done.

So should be main -> pressure reducing valve/filter -> tee off for balanced cold -> check valve -> pressure relief valve -> tee off for EV -> into cylinder. That right?

Pics attached

 

[nashant]

And another piece of data. This morning I turned the main completely off before opening the hot tap. The noise started the same, but was more protracted towards the end and sounded kind of like if you were to twang a big spring.

 

[Trynaplumb]

Issue with the expansion. Pretty certain. Have your engineer, check and recharge or replace

 

[nashant]

Charge is fine, was 3 bar (incorrectly left by installing engineers), has now been set to 2.8 in accordance with manufacturer's instructions. What makes you say EV? Some people saying EV, some people saying definitely not EV. Would love to know what the reasoning behind each answer is. Would whatever issue you suspect the EV has cause a couple of seconds of what sounds like a spring twanging?

Having a read about check valve chatter it seems that turbulence can be a cause, and elbows close to the valve can cause that. Looking at combo valve design and the 4th picture I posted, is it possible that the increased pressure/flow from the EV emptying is causing turbulence in the combo where the check valve is located and causing that to chatter?

 

[nashant]

@ShaunCorbs I've found another thread (noisy non return valve. - https://www.plumbersforums.net/threads/noisy-non-return-valve.87559/) talking about a noisy spring check valve and suggesting a swing valve. Would that be suitable in this situation?

 

[nashant]

I should also add that the pressure gauges fitted to the main swing wildly when the noise is happening

 

[SimonG]

I don't like the ev connected to the combi valve. Prefer to t it in closer to the cold cylinder inlet.

 

[nashant]

I don't like the ev connected to the combi valve. Prefer to t it in closer to the cold cylinder inlet.

That sounds like it might solve the issue if it's chatter caused by turbulence in the valve from increased pressure from the EV emptying. Assume that asking the engineer to cap off the EV outlet on the combi valve, swap the elbow to the cylinder for a tee and take that to the EV would be suitable?

I would like to reiterate that I am not planning on doing this work myself, I want to be able to claim on my house insurance should anything go pop. And for the sake of a few quid that's not a risk I'm willing to take.

 

[nashant]

And it's fixed! Had someone move the EV from the combi to the cylinder cold feed and the problem is instantly fixed.