Appearance of unvented/ mains cylinder

[warwickwater]

I'm a complete beginner I'm afraid, and trying to track down the reason for a discharge of water from the 'overflow' of my mains pressure hot water/ central heating system. As a secondary to this I'm trying to understand the system I have. The house is part of a street of houses all by a small commercial developer and built three years ago. The system is unvented - ie theres no tanks, there two (I think) pressure valves near the cylinder, and theres an expansion vessel above the tank.

My initial question though is - do i have the wrong sort of tank. Mine looks like a 'traditional' rounded end cylinder with a built in hard foam jacket. All the mains pressure cylinders i can find on various 'how it works' web sites and even Ebay look entirely different - with straight ends and looking more like a white painted appliance. They are also very expensive - maybe £500 more than my 'normal' tank.

Has the developer installed the wrong cylinder/ tank to save money? Or do some unvented cylinders have a 'traditional' appearance. There are no manufacturers markings on it, and all connections to it look 'factory' - ie no hacked off lumps of foam and soldering.

Any answers to this possibly naive question much appreciated.

 

[clf-gas]

Posting a picci could be helpful.

 

[GasFitterDeano1981]

Sounds like an unvented hot water cylinder. do you have a pressure relief valve on side which goes to a tundish?
If this is the case and water is leaking from this the expansion baffle inside may need recharging.

 

[Agile]

There are about one manufacturer who makes unvented cylinders which look like that. I think they live in Telford.

But I suspect it may really be a thermal store.

Doesn't it have a name like Telford or Gledhill on it?

Tony

 

[warwickwater]

There's a pressure relief valve coming out of the side that goes to a tundish, and theres a second valve on some of the piper work on the top adjacent to what i think is the mains pressure cold inlet (marked 3 bar) - its next to the pressure relief valve also going to the tundish. There are no makers markings on it at all.

The pressure relief vesssel seems very heavy, and so i assume full of water - do i simply pump it back up with the car foot pump - and if so to what pressure?

Should this recharging be considered routine maintenance or is it a symptom of an underlying fault.

Many thanks in advance for any answers, and much appreciated especially in the absence of pictures or a decent explanation!

 

[Agile]

If it has a tundish then it does sound like an unvented cylinder!

These should only be worked on by somebody who has the appropriate G3 Certificate.. Randomly pumping air into what is the expansion vessel could be dangerous. They should be repressurised according to a set procedure and in accordance with critera based on the working presure.

Does it look anything like this?


Tony

 

[warwickwater]

Thanks tony - it does look somewhat like the smaller, but the vessell is installed discretely (actually just sitting on the shelf in the airing cupboard). the pressure vessel failed about two years ago (at a year old) and the plumber simply pumped it back up with *my* foot pump - he did explain at the time but we didnt really share a common language so i'm still not entirely clear (plumber sent by house builder as in warranty period).

Would putting 10psi (from my research here) in the vesell using a footpump be potentially disastrous, or would this at least help narrow down the cause?

 

[Agile]

Its rather more complicated that that!

The air precharge pressure has to be about 66% of the working pressure but it has to be pressurised with ZERO presssure in the cylinder!

You remind me that its time I went to the Castle Balti again ( and Hamish the dentist as well! ).

Tony

 

[simond]

I would try putting a charge in the expansion vessel for starters. You will have to replace the exp vessel if it has lost the charge, repressurising will only be a temporary fix. If water comes out of the schrader valve it is really shot.

The unit could be an RCM Copperform (www.copperform.co.uk) or possibly an IMI Tribune, which haven't been made for a while.

The IMI ones were quite popular with developers, I assume they were cheap! We have come across one leaking from the cylinder.

Unventeds normally have an appliance quality exterior but this is only for show. The cheapest ones omit this.