Can a hot water cylinder coil vibrate?

[Stephen Luxton]

I have an oil fired system boiler driving a hot water cylinder and radiators through a Honeywell three port mid position valve. Before that we had a Worcester boiler, through a Danfoss mid position valve.

Problem is loud humming/vibration through the pipes around the cylinder, loud enough that it can be heard all over the house.

When the Worcester was fitted about two years ago (whole system from new including stainless HW cylinder and all new radiators), it was fine to start with, and then after a few months it started vibrating badly. After talking to plumbers and research on the internet I decided it was the valve, disabled it and left it in a manual position that didn't vibrate through the winter.

Six months ago the Worcester boiler proved to be a bit of a disaster for unrelated reasons so I had it changed for the current Firebird boiler and at the same time changed the Danfoss valve for a Honeywell. Problem solved, or so I thought. Wrong.

I am not a plumber but do have a reasonable amount of common sense and fault finding ability. Through a process of elimination I have found that

- It doesn't vibrate at any pump speed on CH only
- It usually vibrates at any pump speed on HW only, but worse as the pump speed increases
- It vibrates at higher pump speeds (2 & 3) on both CH + HW
- Vibration is worse when the system water pressure is higher

I have experimented with water pressure and it's best when the water pressure is so low that the boiler sensor only just comes on. Charge it to the proper water pressure of 0.5bar cold and it's a lot worse especially when it heats up to ~ 1.5bar.

At the minimum pressure, which doesn't show on the gauge, the hot pressure is ~ 1 bar, and it is silent on all settings when the pump is circulating and it's all completely cold.

Given that the only common part of the hot water system is the cylinder and pipes (and the pipes are fine in CH mode), I'm wondering if the coil in the HW cylinder is the culprit? It is definitely coming from the area of the valve / cylinder as that is in one cupboard and the system boiler (containing the pump) is in another - there is transmitted noise there but much quieter.

The HW cylinder was about £800 so I don't really want to change it on the off chance but has anybody come across this problem being caused by a coil? I suspect the vibration will eventually break the coil anyway, as it is a terrible noise when it really gets going and you can hear it all over the house.

My other thought is to convert it away from a sealed system, put in a header tank and disable the pressure sensor, which will minimise the hot pressure and get rid of the noise, but I shouldn't have to do this! Is the HW cylinder a possible culprit?

Thanks.

 

[Ch4 plumbing]

Is the cylinder unvented?

 

[Stephen Luxton]

The cylinder is a 210L stainless cylinder vented to above the header tank in the loft. Hot water system is gravity fed from this tank.

There is an immersion in the cylinder as a backup for boiler failure, but it is never switched on.

 

[Ch4 plumbing]

Okay, is their a valve on the return pipe coming out of the cylinder?

 

[Ch4 plumbing]

 

[Ch4 plumbing]

Like this?

 

[Best]

Could still be the coil. But motorised valves can make a din if slipping

 

[Best]

I have just remembered that Telford unvented cylinders now come with addition instructions to insist a 22mm bypass link with a gatevalve on it is fitted across the return & flow to coil.
This is to prevent noise

 

[paulusgg]

Are there any non-return valves installed in the system?

I had a job a couple of years back similar to yours and the eventual cause of rattling and vibrating was identified as a non-return valve that had been installed to correct reverse circulation. A simple bit of re-piping solved the problem.

I doubt very much that the cause of your problems is the cylinder

 

[Best]

I fitted a thermostic cylinder valve once & I accidently somehow fitted it wrong direction. Made a hell of a rattle until I simply reversed its orientation.
Stainless steel coils can also definitely cause noise & Telford cylinders have obviously had this problem.

 

[Stephen Luxton]

Nothing like that anywhere. The HW circulation pipework goes:

Boiler outlet (top of boiler)
> circulation pump (inside boiler cabinet)
> mid-position valve
> coil inlet
> coil outlet
> tee joining it into return from CH
> boiler (through isolation valve inside boiler then into the bottom)

No other valves or fittings are in the HW circuit besides normal solder or compression fittings joining sections of pipe. All in 22mm copper, about 1.5-2 metres of pipe between the two. The cylinder temp is controlled by a stat on the side of the cylinder which sends a hot water demand to the mid position valve. The MPV is a Honeywell 4073A.

So is there an issue with flow rates through HW cylinder coils - is that the function of the bypass, to take some of that flow away?

Thanks.

 

[Stanios]

Bypass is to allow pump overun around the circuit after motorised valves shut but in your case you have a midposition valve which has no shut position so no need for a bypass. You have to really pinpoint the source of this noise, and what kind of noise. You have noise of water going through system, different noise if there is air, and then completely different noise when a mechanical component is operating.

I think save yourself bother and get an experienced central heating guy to check it out.

 

[Best]

If you can't identify the cause of it you should try phoning the cylinder manufacturer technical help and asking is it possible the coil is doing this and what they recommend.
If you use a metal bar or similar against the pipe work and in against your ear, you might be able to find the source of the noise, but noise does travel through the system.

 

[stevetheplumber]

i would try the locksheild valve on the return from the cylinder to slow the flow through itb there should be one

 

[buckley plumb]

Is it a telford cylinder they were bad for that their answer was to bypass upto 50% from the coil had a site of 12 houses with this issue