Expansion vessel central heating

[TMC]

Hi all

Think that the expansion vessel on my Vaillant vcw sine 18 boiler is broken

Pressure leaps up soon after boiler fires up and dumps some water out of the prv

pressure is then low after boiler cools

I think that an external expansion tank is the answer

I have seen them at about 20gbp for the 8 litre I need

My questions are can I just connect it direct into the pipework with 15mm copper without the pressure gauge sold as a option with most vessels (my boiler has a pressure gauge built in) and the 3/4 bsp thread would I use a standard tap connecter on that?

Regards

Tony

[Toby]

I assume you have tried recharging the vessel in the boiler already?

Toby...

[Roger Mills]

The vessel *may* be shot - or it may just need re-charging with air.

There should be a thing which looks like a care tyre valve on the top of the vessel. With the water side unpressurised, measure the air pressure with a car tyre pressure gauge. If it's less than 0.7 Bar (10 psi) top it up with a car tyre pump and then re-pressurise the water system. That might fix it without needing a new vessel.

If water comes out of the air valve, the vessel is definitely shot.

[TMC]

Hi Roger

thanks for this

The problem I have is that I am unsure as to whether I can get to the expansion vessel without stripping out the boiler. I will start to investigate later today and try to recharge it

So the question remains if it is shot then can I just fit a vessel directly to a T in the pipework with I presume a tap connector on the vessel and copper pip?. (That is I am assuming that I do not need a separate pressure gauge on the vessel as shown in the optional kits)

My boiler is on the first floor so my options would be to fit the vessel near the ceiling in the utility room below the boiler, or at the side of the boiler cupboard where it would also need to be boxed in as the current cupboard is too small to accommodate it

Does it matter if the vessel is below the boiler?

Does it matter which way up the vessel is fitted, as in the first location the connection would be neater at the top and in the second would be neater at the bottom?

Cheers

Tony

[Dave Plowman (News)]

Boilers are designed to be stripped for repairs. They're not welded together. ;-) I'd say it's far less work to carefully strip the boiler - take pics etc if you don't have a manual - and replace the vessel than to add an extra one. As regards CORGIE thingies I'd say modifying the system as you intend comes into the same field as stripping the boiler to replace the vessel.

[TMC]

Hi Dave

In many cases I would agree however in my case I would first have to strip out the cupboard built around the boiler to give enough access, then completely dismantle the boiler both water and gas sides to get at the expansion vessel.

In addition the vessel is 114gbp plus vat and delivery where an external one is 20gbp over the counter at screwfix

As the external vessel is only water side and no different to adding a radiator I don't see what CORGI has to do with it, but it certainly would be a consideration if I were to disconnect the gas side

Cheers

Tony

[Tony Bryer]

I admire your optimism, but think that in most cases boilers are designed with the production manager in mind, not the person who has to fix them later. The end result is parts that you need to access are buried behind those you don't (Glowworm CXi condensate trap) and/or require excessive dismantling to get to them which more thoughtful design would have obviated.

I've seem at least one where the easiest solution to the failed expansion vessel problem is just to add another one somewhere else.

[Ed Sirett]

I would suggest that is the solution for 90%+ of systems with failed vessels. See FAQ.

[Dave Plowman (News)]

Ok. Still sounds a bodge to me. And I'm surprised it's considered an economical solution considering the labour costs involved. If the replacement is fitted neatly in a concealed place. This is a pretty large house and I can't think of anywhere sensible I could site one without involving lots of new pipework. But having looked at my Viessmann 200 it appears a simple matter to change the original - although I've no doubt it costs a fortune.;-)

[Alang]

An external expansion vessel is the recommended fix for my gloworm combi. To change the expansion vessel internally would mean taking the boiler to bits.

[Dave Plowman (News)]

I can see that - but still don't think it would be as much work as adding an external one. There aren't *that* many assemblies in a boiler.

[Ed Sirett]

It might be that you are in the 10% where the manufacturers replacement makes good sense. IME, most boilers (not the latest models) would need a lot of work to chance the internal vessel, in many cases removing the boiler from the wall!

[Alang]

This one would have to come off the wall. All pipework disconnected. Lots easier to fit an external one

[Andrew Gabriel]

Gosh, at least that's one thing Keston got right. It lives at the front of the system kit add-on unit and easily comes in and out.

[Dave Plowman (News)]

More or less the same with the Viessmann. Looks an easy job to change any single assembly.

But even if it did mean removing the boiler that's the route I'd take - unless the spare was no longer available.