Worcester Bosch combi boiler expansion chamber leaking

crazydcl

Hi, I am hoping someone can give me some clarification on a boiler issue. I have a Worcester Bosch Greenstar 440 cdi combi boiler, fairly new, so far very happy with it. Next to it at the same level as the boiler is a round red tank with a car/bicycle type valve on top, probably 12inches in diameter and height, directly connected to the cold mains, and with one or two tees elsewhere, I'm at work at the moment so can't check exactly. I assume that this is some sort of pressure expansion vessel with a air-pressurised bladder inside to absorb pressure fluctuations. Unfortunately this has started to leak from the seam around it's midriff, I assume it'll have to be replaced.

However, this is where I have some confusion. The boiler should be under guarantee, but Worcester Bosch say that everything that they cover is internal to the boiler, and that this expansion vessel is nothing to do with them. It's also not mentioned in the manual for the boiler. Unfortunately, I can't get hold of the plumber who fitted it, and CORGI say his registration has lapsed and can't contact him, so I don't know why it's been fitted, and extactly what I need to buy to replace it.

Before I try the lottery of phoning other plumbers, could anyone proffer an opinion please on any of my confusions:

Why is it there? What is it called if I need to buy another one? Do I need the same one, or can I buy a different one that might last better? Does the fact it's leaking indicate a possible failure elsewhere? CH pressure is correct at 1 bar, and normally only needs topping up once or twice per winter.

Thanks in advance for any help.
Cheers - Dave

ariba10

It is a pressure expansion vessel, there is a membrane inside with compressed air on one side of it and the CH water the other.

The schrader valve is to make up the air in cases where it is lost.

As the water expands as it heats up the expansion is taken by compressing the air further.

I have not known of one to leak myself but have not had a lot to do with them.

I should imagine they could be changed.

EliteHeat

crazydcl wrote: »

Why is it there? What is it called if I need to buy another one? Do I need the same one, or can I buy a different one that might last better? Does the fact it's leaking indicate a possible failure elsewhere? CH pressure is correct at 1 bar, and normally only needs topping up once or twice per winter.

It is there as either a leftover from an earlier non-naturally pressurised boiler or because you have a large system that needs the additional expansion capacity that this vessel affords.

They come in standard sizes, 12 litre, 18 litre etc - screwfix carry them

If the vessel is leaking water through the valve then this indicates a membrane failure. If it is leaking air then it is just a failed valve.

If it is leaking water and your system is continuing to run normally then you didn't need it anyway and it is probably OK to get someone in to safely decommission and remove it.

Steve_PS

Your pressure vessel may look like its connected to the mains but I can assure you it shouldnt be and probably isnt. It should be connected to your sealed central heating water system. As an ex CORGI CH engineer, I have worked on the same boiler you have fitted and it has an integral pressure vessel fitted internally. Your boiler should have a pressure gauge fitted, indicating your system pressure. The vessel is fitted to allow expansion when you system water temperature rises. As water wont compress, the air contained within the vessel does. If your external pressure vessel is leaking it needs remedying. If it is connected as part of your CH system, this system will eventually loose its pressure through the leak and the boiler will shut off as a safety measure. If it was fitted to the system for a previously used boiler it can be removed completely; I would doubt it's there to complement your existing boiler but not knowing your boiler's history its possible that it was fitted to 'replace' your boilers original vessel if it was found to be leaking internally as an easier alternative to replacing the original. I suggest you get a CORGI engineer to look at it; he can look at you boiler as well to ensure everything's working OK.

EliteHeat

Steve_PS wrote: »

Your pressure vessel may look like its connected to the mains but I can assure you it shouldnt be and probably isnt. It should be connected to your sealed central heating water system. As an ex CORGI CH engineer, I have worked on the same boiler you have fitted and it has an integral pressure vessel fitted internally. Your boiler should have a pressure gauge fitted, indicating your system pressure. The vessel is fitted to allow expansion when you system water temperature rises. As water wont compress, the air contained within the vessel does. If your external pressure vessel is leaking it needs remedying. If it is connected as part of your CH system, this system will eventually loose its pressure through the leak and the boiler will shut off as a safety measure. If it was fitted to the system for a previously used boiler it can be removed completely; I would doubt it's there to complement your existing boiler but not knowing your boiler's history its possible that it was fitted to 'replace' your boilers original vessel if it was found to be leaking internally as an easier alternative to replacing the original. I suggest you get a CORGI engineer to look at it; he can look at you boiler as well to ensure everything's working OK.

What was the point of writing all of this down? it has already all been said, the only difference being that the previous posts were at least legible.

Steve_PS

What was the point of writing all of this down? it has already all been said,

LOL, and you are the MSE police then are you? If you can't understand it, enrol for a few English lessons in your local college.

crazydcl

Thanks for all the replies. However, I've checked, and it is most definitely connected to the cold water supply. From the stopcock, there is a branch to the washing machine, a branch to the kichen, a branch to the toilet and bathroom, a branch to the supply side of the boiler filling loop via a scale inhibitor, and finally it ends at the expansion vessel. All of this is a new (year and a half old) installation with no remains of an old one - it's in a small utility cupboard in part of a kitchen extension, all fitted new by the same plumber.

As far as I can tell, putting a non-potable expansion vessel in the cold water supply is not normal practice?? I can only assume that the original plumber put it in either for water hammer suppression?, or to take up expansion of the cold water when the stopcock is closed!?, or because he thought he needed an extra external tank and then changed his mind (11 radiators in the house, most fairly small).

As far as I can see, my options are either to blank it off, or remove and fit a water hammer suppressor, or remove and fit a potable expansion vessel. I'm inclined towards the water hammer suppressor, unless anyone can think of a good reason why it might have been fitted and needed. Unfortunately the (then CORGI registered) plumber has deregistered and vanished (Spain probably!) so I can't ask him himself.

blinghill

i note that my new expansion chamber has been prepressurised to 1.5bar. As my heating system runs at approx. 1bar do i need to deflate it to 1bar for it to function correctly ?
any ideas ?