Loft radiator needs constant bleeding

[nadimaj]

The "Last" radiator in the house is in the loft. It makes a near constant (I'm gonna say) "hammery" sound when the system is on. When I bleed it an extraodinary amount of air comes out (sometimes for 10-15 seconds) before I get water. Things settle down for a few minutes. Then literally 2 minutes later, the noise is back. I go for a second and then third bleed, and yes, the amount of air that escapes becomes less and less but give it a few days and that extreme amount of air is once again back. The rad heats up quite well but the noise is still there.

Newly done home with every thing brand new. The plumber has already been around twice. He does a bit of a "balancing" act by bleeding air out of the rads in a certain order whilst reducing/increasing the flow valves when he comes and eventually gets the system ticking over nicely. But then the problem is back in less than a week.

I gather sometimes this issue is due to a bad pump so I suggested to him that the pump might be "over pumping". Something is generating the air right? He does what most tradesmen do, they don't consider your opinion because you're obviously a numpty! Instead he has suggested I buy those constantly venting valves or buy a noise reducing chemical. But that's not root cause fault finding is it?

Thoughts? What 2 or 3 things would you look at or try next?

Thanks!

 

[Harry Bloomfield]

How long since it was first commissioned? It can take a while to get all of the air out of a system, and usually it will mostly collect in one radiator, usually the highest one.

 

[nadimaj]

It was commissioned early October 2022

 

[Bod ...]

Is it a sealed or vented system?

 

[Johntheo5]

Is the circ pump internal/external, if external post the make/model/setting, if internal, the boiler make/model.

 

[nadimaj]

Thanks guys,

Boiler, stuff under it, pump attached to tank, manifold, manifold pump.

 

[Johntheo5]

How many pumps are there in all?
The "warmer" is the UFH manifold pump,
What does the Wilo supply?
Is there another pump that maybe supplies a low loss header?
Can you see which one supplies the rads.
What is the boiler system pressure?

 

[nadimaj]

The Wilo loops in and out of the tank. So no factor.

Only that orange pump attached to the manifold I can see. Otger than the black and gold Valiant block, nothing else.

Boiler pressure 2.0 bars but its on right now, I would say 1.5 when off from memory.

 

[Johntheo5]

The Orange ("Warmer") pump is the UFH mixing UFH manifold pump so IMO can't circulate the rads, there may/must? be another pump maybe in the boiler itself that supplies water to the UFH pump and probably circulates the rads, the Vaillant is a system boiler so should have its own pump I think. I can find a emanual for a 376/5/5A but not for your 386/5/5A. You might look at the "d" parameters, around d.027 etc for more info.
That said, there should not be air ingress with a cold system pressure of 1.5 bar, it may be a symptom of some other gas buid up. If it is air then the system shouldn't need topping up after venting?.

 

[nadimaj]

Correct. I never have to top up after venting unlike my old place. I'll have a look at the manuals. Cheers

 

[nadimaj]

Bumpety bump

 

[Johntheo5]

Make a few assumptions.
One: that air is being ingessed even though the system pressure is > 1.0bar, it means that some part of the system is under a vacuum, like a automatic air vent, maybe check boiler AAV shut off or maybe the UFH manifold return is drawing in air , can only suggest isolating the UFH at the manifold for a day or two to see if problem persists. Only other, very unlikely reason is that the system has been plumbed with non barrier piping in part.

Two: that it is not air but some gas or other being generated in the system due to corrosion etc, can't suggest anything there I'm afraid.

 

[Bodgedbuild]

I wouldn't go so far as to recommend trying this but excess use of flux (causing corrosion) or unexpected current flow (causing hydrolysis) through heating parts can cause hydrogen build up which is flammable. As far as current flow I believe the use of a mixed metal and plastic plumbing with no earths in certain areas can make them exhibit a "floating voltage" that actually shows up on a multimeter.

 

[nadimaj]

Blimey

Thanks for the tips both, I'll obviously start of with yours JT