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

nashant · Oct 19, 2023

Hi all. As the title says, I have a problem with an unvented cylinder I had installed last year where the first time I turn a hot tap on after the cylinder has been heated I get what sounds like a vibration. It generally starts about 1s after I open the tap and lasts for about 1.5s. I've attached a recording, the start of the recording is when the tap is opened.

This problem has been ongoing from the start but seems to have gotten worse in the last 6 months. The company that did the install don't seem to have a clue and now are pretty much trying to wash their hands of the situation.

A bit about the system...

ATAG i32s boiler in the kitchen, primary flow and return go up to the cylinder in the loft, about 13m away before coming back down on another 8m run before they tee off for any rads (is this normal? Means that hot water has to travel over 20m, and up through the unheated loft before seeing a rad).

250l Joule Cyclone Plus in the loft, with Caleffi valve set to 3 bar, and 19l expansion vessel. One side of the valve has cold main on top and balanced cold on bottom, other side has EV on top with cylinder feed on bottom.

Flow rate to unrestricted tap straight off main is about 18l/min.

Pressure on main is about 4 bar, rises to 5 bar after a heating cycle on the cylinder.

Pressure on the hot is 3 bar normally, rises to 4 bar after a heating cycle.

Sure there's some information I've left out, if so please do tell me.

Any suggestions would be so gratefully received, got a whole house renovation to project plan before January, a new baby to take care of, and a day job to do. Could really have done with not having to think about this!

nashant · Oct 23, 2023

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 · Oct 23, 2023

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

nashant · Oct 23, 2023

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 · Oct 23, 2023

@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 · Oct 23, 2023

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

SimonG · Oct 23, 2023

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

nashant · Oct 23, 2023

SimonG said:
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.