Flat expansion vessel

26 Feb 2007
Reaction score
United Kingdom
I have a combi boiler (Sauvium Duval Thema Classic 24) in my flat which is about 4 yrs old and recently stopped working. I have tenants in the flat which makes it difficult for me to access but a plumber has apparently visited and said

"the system is loosing pressure because the expansion vessel is flat causing a pressure loss each time the system gets hot (I.e. the expansion vessel is not allowing for the increase in pressure when hot)."

"The expansion vessel for this boiler is £100.18+VAT plus £10 carriage. The filling loop is also gone, these are around £10+VAT"

"To fit the new expansion vessel it will be necessary to remove the boiler from the wall, because the expansion vessel is in the back of the boiler (bad design!). The total time is going to be around 4 hours(£65 per hour)."

So the total cost is going to be 260+100+10+10+VAT = £380 + VAT

My initial thought is why is the expansion vessel flat? Is it a design fault?
Would the costs and labour be regarded as reasonable?
Is there a cheaper way of solving this problem?

Sponsored Links
if the filling loop has gone then you will be unable to pressurize the heating system...put in a new filling loop...fill system up to 1.5 bar pressure...then check to see if system loses pressure
Expansion vessels go flat over time. It happens.

Can it not be repaired? Read posts in FAQ about repressurising e/vessels.

the cheaper way to repair it would be to leave the one behind the boiler in and use a remote expansion vessel on the return pipework.

not always the best option if you are tight on space but its an option none the less
Sponsored Links
The flexi hose to the exp. vess. block on this boiler giving the same fault as a faulty exp. vess.Normally you can pump the vess. back up to 1 bar they rarely need replacing.On the odd occassion i have replaced them it normally takes 2 hours,3 hours max if in a difficult position.
expansion vessel pressure is usually checked each service. Why can't this be re-pressurised and then see what happens! Don't know this model but others with exp vessel at back (right royal pain in a***) usually have access just for valve to re-pressurise.
Thanks everyone for the feedback.

I'll get the guy to change the filling loop first then re-pressurised to 1.5 bar to test. If pressure still being lost then I guess I will have to bit the bullet and ger expansion vessel replaced. The guy recommends replacement so it seems he doesn't think the expansion vessel is repairable. I don't know enough about this to argue with him. Unfortunately not enough space to fit a remote expansion vessel on the return pipework.

Seems like his 4 hr estimate to do this replacement (if needed) is an hour or 2 longer than it should take.

Thanks for your help.
I wouldn't accept the replacement job if I had to do it in 2 hours. 4 isn't unreasonable imho. Suppose it leaks - and boy how sd's love to leak.

But you're missing the point. Read the faq, The PV only needs replacing if it's faulty, not just because it's lost pressure - bicycle pump should resolve. If it's full of water instead of air then yes, it's dead.
The plumber apparently came back and said he can do the job in 1.5 to 2 hrs so I said go ahead.

I'm having trouble finding the FAQ for expansion vessels on this site. When I click FAQ I get a list which seem to relate to "Login Preferences" & Settings etc so I guess I should be going to another page. Can anyone help? I'm not too familiar with his website yet.

Quite a few instruction manuals recommend an external vessel as a replacement rather than the boiler off the wall.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links