Faulty expansion vessel?

[Fixit]

I am a caretaker for a small primary school. An Andrews unvented hot water heater supplies the hot water in the kitchen. I've noticed a drip from the discharge pipe and prior to calling in our plumber would like some advice. I have opened the temperature/pressure valve; this lets water shoot out of the discharge pipe. Upon releasing the valve the flow stops to a constant drip (faster then the drip already coming from the discharge pipe). This takes a while to reduce to the flow of the original drip.

I also checked the expansion vessel, which sits on top of the pipework supplying mains water to the unit (using a tyre pressure gauge). When I did this water spurted out. Am I right in thinking that the expansion vessel is probably had it. If so can any plumber carry out he work or does it have to be one with CORGI registration or an unvented hot water certificate? Usually the council dealt with this direct, however this has now changed.

Any advice on the matter would be greatly appreciated.

 

[ChrisR]

You're right about the expansion vessel's demise.
Might need a new pressure relief valve, or it may be cleanable, or it may only be dripping cos the water's expanding and the PV is full of water.

If the amount of stored hot water is more than 15 litres, which I imagine it is, anyone working on it has to have the Unvented card.

 

[Fixit]

Cheers Chris,

One thing I didn't mention is that the water coming from the discharge pipe is cold and I belief is coming from ther expansion valve. Due to the school's budget I would obviously only want to change what was broken.

Is it likely that the expansion vessel is beyond repair and this has damaged the expansion valve or am I right in thinking that the expansion valve is doing the job is was meant to do?

 

[oilman]

It's probably the expansion vessel. and the expansion valve may also have a problem, but one step at a time.

You MUST have someone who is registered to work on the cylinder and it's attachments, ask for their registration number before they start.