We have a conventional central heating system which is probably 20-years old but has a new Worcester boiler which was fitted earlier this year. (Not a Combi).

We've always had a problem with air in the rads which I have to bleed every month or so and also in the hot water which dramatically reduces the flow unless I purge it occasionally by connecting the mains to a hot water tap.

We had hoped the new boiler and contriols would solve the problem but it's had virtually no effect.

Any ideas what's likely to be the cause.

I've been told it could it be a leak in the hot water cylinder between the coil and main tank but don't understand why even this would cause the problem.

John.

I would suspect you either have a pinhole in one of the pipes that is sucking in air..

Or, you could indeed have a crack between the coil and the water cylinder...

As a cheap fix... you could potentially fit an automatic air bleed to the highest point of the water AND heating systems to try and reduce the amount of air that gets circulated about...

Also check you have enough head, i.e. that the header tank is high enough to keep the system under slight pressure, the boiler should specify how much head it needs.

Too little can cause air ingress into the system at the high points, which is usually the coil in the hot water tank.

are you sure it is air? Corroding steel radiators produce hydrogen when they react with water in the absence of oxygen. Light a match when bleeding, you'll get a nice pop if it is hydrogen.

r1_pete


The header tank is probably 5ft above the boiler but very little above the hot cylinder (probably only 1ft or so).

We're in a bungalow and both the cylinder, cold tank and header tank are in the loft.

The heating system however does run under the floor (ie. it's not a drop system).

John.

if your in a bungalow i would expect it to be something to do with your tank
Does it ever pump over the vent pipe?
What setting is the pump on?
you need to sort it really not just keep bleeding the air out because when the new water is filled into the system it is fresh with oxegen so will speed up the corrosion of the system.
if you cannot resolve the problem one thing i would sugest is putting a unvented kit in place of the tank not very expensive and would stop this problem straight away only thing is the system would be under pressure then so you have got to think if your rads/pipework will take it

adam1985

Yes, it has pumped over which I noticed bacause the water in the expansion tank was quite warm but since then the guy who installed the boiler turned the pump down one setting.

I did think about dispensig with the header tank because I believe you can use a sealed system but at a much lower pressure than the 2 bar or so used by combi boilers.

I am just a little nervouse about the old pipework which is under the floor and most of this is now covered with laminate style flooring making inspection very disruptive.

Is it hard to convert from a header tank to a sealed system?

John.

No its pretty simple really if you get a kit they come with all the instructions and you just need a few connections.you will need to double check with your boiler man to check they allow you to do it but im sure you can with worcesters.

Or

There are a couple of things to try on your system now.

Try it with the pump on the lowest setting and see if that stops it pumping over and still gets everywhere warm.

If not you can extend the vent pipe so it loops higher up over the tank so the pump has to push it alot higher for it to pump over make sure it ends back in the tank though.

Or you could spiral the vent pipe round like a spring if you dont have much hight its not the prettiest but i have known it to add enough resistence in the past to stop it pumping over

[Edited on 7/12/09 by adam1985]