Overpressure in System?

[kenny4]

Hi I hope someone can help as I have had two plumbers come to me and do nowt but scratch their heads?

Problem is quite hard for me to explain as I am not a plumber but will give it a go-Basicly I have noticed for a while that when my hot water is on ie boiler is heating up that I was getting a good leak from my overflow outside about 1ltr an hour,so I managed to trace it to my hotwater tank where their is a pressure relief cold water 4 bar valve that is connected to the hot water tank as well as a drain one for the tank .
Yes I thought I will give it a clean and or if it still leaks get a new one tried to clean first,no it wasn't that so bought brand new valve at a cost of £48 and thought that that would be the end of it(I wish).
Leak is still there so called plumbers who said that it was a faulty valve and replaced free fo charge.Still leaks?

So I am at my wits end as it is dripping away a nice puddle on my drive everytime the hot water clicks on to heat up?
Is there overpressure of 4 bar in the back of this valve and if so how can I reduce it so that the leak stops(just before the valve is a large reducer valve of some sort from cold water mains?

Any ideas

Thanks

 

[ChrisR]

What you have is an Unvented Domestic Hot Water Storage System. Anyone who instals or works on one of these must be registered to do so, and will have card to pove it. The reason is that they can explode, taking all of your house with them. They should be serviced annually.

There are two basic types: one has a separate pressure/expansion vessel, which is a blue or white presssed steel thing with a seam around the middle. With the other type (such as Megaflo) the expansion happens in an internal air pocket at the top, which you can't see.

Megaflo's (make) don't use4bar valves, so I shan't guess. You may well have to recharge the expansion device with air - let us know what type you have. You do not need to be registered to do that.

The water expands whenever it's heated, and if it has nowhere to go it comes out of the pressure relief valve.

 

[kenny4]

At Last Someone who knows what he is on about-Thank you!

Yes I seem to remember some asking for a bicycle pump one day,I do have one of those expansion type thingys and it has no name on it but has a silver ring round the middle and has a air type inflation valve at the bottom.
Do you think that will solve it?

I am gratefull for your reply Chris

Roy

 

[ChrisR]

Undo the cap from the schraeder type valve (like car tyre's) on the pressure vessel. Press pin with finger nail. Does water come out - it definitely shouldn't.

Turn off water supply to the cylinder. Open a hot tap (does much come out? - it shouldn't) .

Connect car foot pump to the valve - what's the pressure?
Consume Weetabix.
Pump by hand to get pressure up to 3 bar (45 psi).

Turn on supply to cylinder
Turn off hot tap.

Done

But while you're there, find the 2 red knobs - one's atemp amd pressure relief, other's another pressure relief. Twist one against its spring , then the other, then both. In all cases water should pi55 out via tundish (open funnel thingy) to a safe place, without overflowing the tundish. NB in fault condition this water would be scalding. Them knobs usually pling shut if you turn them a bit more. ANyway, when they're both shut there shouldn't be anything running throughthe tundish.

Those presssure vessels usually hold pressure for years. If water came out of the tyre valve its rubber diaphragm is perforated & you'll need to get the pv replaced

 

[kenny4]

Just done what you said Chris and water came out of the valve ,so I take it I will need to get a new diaphram fitted(problem found at last).

Well I am very impressed by your responce to me Chris and it seems i have almost found what seems to be the trouble,I can now arrange for a new diaphram to be ordered and fitted and will make sure I get somone qualified to repair it.Unless you fancy some Cash work he he ....

Many Thanks Again You are a Star

 

[oilman]

kenny4, it is unlikely the diaphram will be replaced on its own, but as ChrisR said, the pv (pressure vessel) also known as expansion vessel, will need replacing.

Unless you can find someone yourself who is certified to work on your system, you could try contacting the manufacturer who will have a list of people who are.

Which part of the country are you in?

Just as an anecdote, if all of the uv-vented cylinders fitted in the past year, were fitted by certified operators, we would all be fitting three a day. Makes you think.

There are quite a few posts on this forum about un-vented cylinders if you are interested. Take note of ChrisR's warning about these things, on courses they show several pictures of what were buildings after the cylinder has finished with them.

 

[ChrisR]

Yes I meant change the whole vessel. Make sure nobody tries to sell you a red one, they're for heating systems.