Trapped Air in Cylinder coil

Hi there

Please can anybody advise me on how I can get air out of my DHW system . I have a Y plan system but the coil inside the cylinder has air trapped inside.

I have tried switching the 3 way valve to open but that does not help. there is an AAV on the pipework just after the 3way valve, but when the system is on hot water only I cant see how it vents ?

Thanks for your understanding. View media item 40979

I cant see how it vents ?

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It won't vent the coil fitted where it is. To do that it needs to be fitted between the Honeywell valve and the cylinder connection.

I've got to say the layout of your pipe work is terrible!! with a little thought the pipe work could have been installed much better and the pump in particullar put in a much more accessible position

as a service engineer I hate having to replace components installed like that!!

Thanks 45yrs a gasman for your reply . You have helped me on 3 occasions now

Only thing you can do is crack open the nut on the 3 port side into the cylinder

Boilerman2
Thank you for your comment
You are absolutely correct. Would it be worth me considering getting a heating eng to change?

You could try opening the FLOW nut into cylinder a little and see if the air escapes ,then retighten it as soon as water comes out, you may get some water with the air do not woryy though. It is a method I use when pipeing such as yours is encountered.

Yuo might find if you turn off the power to the system, then manualy open the mid position valve (this will put the valve to mid pos i.e. all ports open)
the air might find it's way through the 3 port valve up to the AAV and away

My tuppenceworth:
- you're all going off at a tangent...!
There isn't going to be any trapped air in there that the current AAV won't sort out, IF it's working properly.
For it to work properly the black plastic screw on the top has to left loose. Usually they scale up and leak if left loose, and people shut them, so they can't leak, but also the AAV can't work.

You don't get problems with small amounts of air because air dissolves in the water, over time.
If your system is generating air then you have a problem which will cause other trouble - letting it out will not solve the problem.

Coils themselves do not, ever, "trap" air, the pipe inside goes down towards the outlet underneath!
If you think your HW is slow to heat, chances are that you're right, but it's because you have a cheap cylinder there with a very short heating coil. Better ones have the connections further apart.

Someone suggested unding the nut where the fitting goes into the cylinder - totally impossible, it's an elbow screwed in! The fittings on the cylinder are best let alone if they've been in for a few years. Moving then is likely to cause a leak needing a new cylinder.

SO - put the valve in the "MAN" position, undo the black plastic screw - sometimes they stick in. If it has, undo the nut underneath the AAV. If air comes out then you need a new AAV.
The sirtof layout you have isn't ideal but a large proportion of the nation's houses has the same or worse, and no air problems.

Your pump spindle should he horizontal, bu the way, they don't have an "end" bearing.

Also I see the drawing is marked up for an ABV - you don't need one on a system with a 3 port valve, as long as there's a rad somewhere which is always open. ( Unless you have a monster boiler or something like a Keston)

Er coils do trap air and you can throw all the scientific crap you normally do at me, I've seen a few, all Piped up badly, as I said in above post, bucket underneath nut will normally shift

you're all going off at a tangent...!

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I disagree, the advice given is sound basic plumbing advice on what is poor system design. Fitted where it is the AAV has little chance of venting air from the cylinder.

Sloping pipes with an exit at the top don't trap air. Is that too scientific?

If moving the valve to Manual doesn't release any air, it's not because it's "trapped in the coil". This one is clearly not installed horizontally - which we've all seen.

The AAV should only need to let air out on commissioning, there shouldn't be any after that. If it's an open system - which it is if those are the vent and feed behind, then of course air should be going up the vent.

Poor system design as displayed in the picture isn't the Doods problem. We can see several things "wrong", none of which is going to give a trapped air problem. If there's air being generated, the problem's somewhere else.

That would all be true even if we were NOT in a season when the 3 port valve is obviously going to be opening to the CH side frequently which DOES have the vent attached.

Dood have you tried venting that badly installed pump?
If you're generating air it will trap it, at that angle.

Dear all

Very interesting and informative reading, Thanks. In answer to the latest question Yes i have vented the pump several times, usually after I hear a gushing sound.

When the HW only is swithed on there is a lot of gurgling, hissing and banging coming from inside the cylinder?

The system has always been bad to fill etc since we moved in. Added problem now the Boiler keeps cutting out.

It's darned hard to tell exactly where noises come from, they transmit along the pipes so well.
The pump needs attention - it could be sticking. That would make the boiler overheat, which would make the banging and hissing noises. Also a pump full of air won't be pumping anything

As I said, if moving the lever on the motorised valve doesn't release any air then the AAV isn't working, you DO NEED to check it, but with the Vent pipe a couple of feet behind the pump ( by the look of it) you should have got rid of air anyway.

If you can slacken off the nuts on the pump connections ( the ones on the pipes may be easier, than the bigger pump flange nuts) and twist the whole thing horizontal, I suspect your problems might go away.

As I said, the configuration of the AAV & associated pipes is wide open to criticism, but it is not causing the problem, and moving things there would not "make up for" your pump problem.
90% of systems simply DO NOT HAVE a permanent air vent to bleed the coil automatically - it shouldn't be necessary.

NB if the pump isn't working properly, then if the water in the boiler overheats it will produce air separated from the water, & steam, which will make the pump situation worse immediately. Your "gushing sound" is likely to be a rush of steam shooting over the vent pipe into the header tank. This is a BAD THING!
And also, too, as well, longer term, you'll be accumulating oxide deposits in the pipes particularly where the vent and cold feed join in to the system - and they can ALSO block things up.

A gushing sounds means you have oxygenated water in your system. That means you will eventually get corrosion & sludge in your radiators. A corrosion product is hydrogen. It generally collects in radiators where it's produced - do you have to bleed radiators periodically? You shouldn't have to, ever. You would get some being separated in the boiler, but too slow to be causing the acute problem you have.

So fix the pump!

Doods said:

. Would it be worth me considering getting a heating eng to change?

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Don`t bother with a " heating engineer" - you pay for their Gas Safe quals. which are not needed for this job - get an old school plumber - if you can find one in London