Unvented central heating system sounds like kettle!

[TomMs]

Can anyone suggest a solution or help?
When my timer starts both heating and hot water, there are two motorised valves (one for hot water and one central heating) there is No noise from the pipes. However, when the hot water reaches temp and switches the motorised valve off the noise starts! It sounds like a kettle and is loud. Difficult to pinpoint where but sounds more from the return Pipework. The noise stops if I manually push the lever on the hot water motorised valve to open. Close it again and the noise begins. Hot water only on and there is no noise. So I can deduce the noise is from the central heating not hot water. I just changed the heating motorised valve which didn't help. I bled the system no benefit (the water was clear coming out). Inhibitor added annually. I opened all the Trvs and lock Sheilds no luck. Varying the pump speed has no effect. The pump sounds ok. Grunfoss and only 6 years old. The expansion vessel is correct pressure. The system heating is fine and running at 1.5 bar. All radiators have bidirectional valves fitted. All radiators are fairly new staggered fitting in last 6 years. 11 rads and 2 towel rails. New Worcester condensing boiler fitted 3 years ago. Can't pinpoint when or any specific change that started this but the noise is driving us mad!

 

[picasso]

Google bypass valve and see if you have one fitted to your system.

 

[TomMs]

Appreciate the advice Picasso. I checked and I don't have a bypass valve. System fitted before BR requirements. There is a bypass though. A radiator with 2 lock shields both open. It's cut in (flow) between pump and valve switches as per a bypass should be, then to return. Would this not be enough if a little less efficient? Also the noise happens from cold so all radiators would be open. Noise only stops when hot water on. I'm at a loss!

 

[dilalio]

Maybe the HW valve is not fully shutting!?

Edit: You could try taking the actuator off and holding the spindle closed with pliers/adjustable to see if the noise stops!

 

[TomMs]

Thanks Dilalio. Took actuator off and closed spindle with pliers. When fully twisted to close then noise starts. Small portion of travel at end to close and the noise is there in earnest! Any other ideas more than welcome.

 

[picasso]

Sure the bypass rad is open ?

 

[dilalio]

Is the noise affected if you change the speed of the pump?

Is this a recent manifestation?
Would you say the noise is a mechanical or heat based noise... "kettling" is the description you gave which is from water 'boiling'

Are any pipes loose/ knocking against something?

Edit: just seen you changed pump speed, so scratch that!
Try closing all but one rad and see if you can affect the noise by moving around and changing the open rad, one at a time!

 

[TomMs]

Hi Picasso. Thanks for comment. The bypass rad is definitely on. Nice and hot and both lock shields work. It sounds like the return pipe is the caus of the noise. The flow doesn't make much noise.

 

[TomMs]

Hi Dilalio, not sure how long being going on. In last winter so heating just on this season and noise always been there. The noise sounds water/heat based. Like a washing machine filling up or a rush of water or a kettle. Seems to be return and not flow. Drains system again today and changed cheap Trv which didn't work. It doesn't sound like knocking to honest and all visible pipes seem well secured.
As per your suggestion. Closed all rads (except bypass rad). Heating on. I put on all rads full downstairs (one at time) and no noise heard! I then put on upstairs extension(one at time). Extension rads upstairs and downstairs on "separate circuit". This circuit Flow cuts from flow after switch in airing cupboard (housing pump, valves, expansion vessel, bypass rad) up to loft through to extension upstairs then downstairs and back. If that makes sense. Still no noise. There are 3 rads and one towel rail left not on. However when I turn any of these 4 on he noise stats immediately. So in essence the upstairs rads in the original part of the house if switched on cause the noise. Whichever one is switched on. There is no air in any of the rads. I bled them all. I need upstairs heat for two young kids. But the noise wakes everybody up early morning so real pain. I'm out of ideas! Any ideas warmly received.

 

[picasso]

Take the heads off the trvs and see if the noise is still there.

 

[TomMs]

Hi Picasso, issue pinned down to 3 rads and 1 towel rail rad (see below) Turn any of these on and the noise starts. Taking the trv off these doesn't make a difference unfortunately. Any other thoughts appreciated.

Closed all rads (except bypass rad). Heating on. I put on all rads full downstairs (one at time) and no noise heard! I then put on upstairs extension(one at time). Extension rads upstairs and downstairs on "separate circuit". This circuit Flow cuts from flow after switch in airing cupboard (housing pump, valves, expansion vessel, bypass rad) up to loft through to extension upstairs then downstairs and back. If that makes sense. Still no noise. There are 3 rads and one towel rail left not on. However when I turn any of these 4 on he noise stats immediately. So in essence the upstairs rads in the original part of the house if switched on cause the noise. Whichever one is switched on. There is no air in any of the rads. I bled them all.

 

[picasso]

I reckon its one of the trvs vibrating, try shutting down a lockshield valve on each rad in turn and see if you can narrow it down to one rad.

 

[TomMs]

Hi All
I had narrowed it to the 4 rads as mentioned. I changed the trvs and lockshields to new Drayton. Didn't solve issue on my s unvented system.
In fact the situation is strange.
Heating on and all rads shut(except bypass rad): No noise
Heating on and extension rads open (copper pipes to attic and then plastic distribution in extension): No noise.
Heating on and rad on in original house: Noise (before it was only the 4 upstairs).
Heating on and HW on: no noise.
However, now if the pump is on med or high speed the noise exists even with the hw on.

Could it be an air lock? All rads are bled.
Could it be the pipes? The water is clear out of the.
Would a good limscale or cleaner run via system have any effect or more money for no resolution?
Could it actually be pump. Indications are it works fine. Don't want a new one and find old one is fine.

All help apprecieated as we are going insane with nose and frustration on cause!

 

[picasso]

Non return valves are sometimes installed to stop unwanted circulation, they can become noisy when worn so might be a nrv hidden away somewhere.

 

[dilalio]

You'll have to treat this like a leak!
Archaeology until you pinpoint the faulty fitting/pipework it would seem! Sorry, but I can't think of another solution without being there!