Hot water tank and leaking pressure relief valve

Escapees

Have a problem with the heating system setup in an apartment. Basically the pressure builds up in the hot water tank when it's heated and causes the relief valve (6 bar) to leak. It's a closed system with a booster pump, an expansion tank/vessel and a pressure reducing valve (in that order) before the hot water tank. It looks like the pressure reducing valve acts as a non-return valve in the system and I can see the pressure build up on the gauge (going to max readout of 5 bar!) when the tank is heated.

To me it seems like the expansion tank is located on the wrong side of the pressure reducing valve. Or else there should be a non-return valve bypassing the pressure reducing valve to allow any pressure buildup to release to the current expansion tank. But I'm no plumber! So, what's the normal configuration for this type of system which I'd say is fairly common, especially in apartment blocks?

Escapees

Escapees wrote: »

Have a problem with the heating system setup in an apartment. Basically the pressure builds up in the hot water tank when it's heated and causes the relief valve (6 bar) to leak. It's a closed system with a booster pump, an expansion tank/vessel and a pressure reducing valve (in that order) before the hot water tank. It looks like the pressure reducing valve acts as a non-return valve in the system and I can see the pressure build up on the gauge (going to max readout of 5 bar!) when the tank is heated.

To me it seems like the expansion tank is located on the wrong side of the pressure reducing valve. Or else there should be a non-return valve bypassing the pressure reducing valve to allow any pressure buildup to release to the current expansion tank. But I'm no plumber! So, what's the normal configuration for this type of system which I'd say is fairly common, especially in apartment blocks?

The expansion vessel should be fitted as close as is practical to the cylinder on the cold mains feed to the cylinder, it can also be fitted to the combination valve which does incorporate a check valve but doesn't impact on expansion.

You have a issue obviously as leaking water is the first sign of a problem so you need a plumber to check over the installation to confirm it meets manufacturers instructions and to also check the expansion vessel is set/positioned properly and is doing it's job.

cruiser202006

Sounds like vessel is in wrong location. If it's before pressure reducing valve/inlet valve then it's not doing anything for the cylinder and it's blowing off on the t&p valve when it's heated up

Escapees wrote: »

Have a problem with the heating system setup in an apartment. Basically the pressure builds up in the hot water tank when it's heated and causes the relief valve (6 bar) to leak. It's a closed system with a booster pump, an expansion tank/vessel and a pressure reducing valve (in that order) before the hot water tank. It looks like the pressure reducing valve acts as a non-return valve in the system and I can see the pressure build up on the gauge (going to max readout of 5 bar!) when the tank is heated.

To me it seems like the expansion tank is located on the wrong side of the pressure reducing valve. Or else there should be a non-return valve bypassing the pressure reducing valve to allow any pressure buildup to release to the current expansion tank. But I'm no plumber! So, what's the normal configuration for this type of system which I'd say is fairly common, especially in apartment blocks?

cruiser202006

cruiser202006 wrote: »

Sounds like vessel is in wrong location. If it's before pressure reducing valve/inlet valve then it's not doing anything for the cylinder and it's blowing off on the t&p valve when it's heated up

Without sounding like a contrary Sod you could be absolutely right or as Unvented cylinders should be fitted with a combination valve and it does more than just a pressure reducing valve, some manufacturers allow the expansion vessel to be plumbed in to the combination valve, so again depending MI you could be absolutely right or the plumbing is fine and the vessel needs a bit of love.

cruiser202006

Have you got a picture of the setup??

Escapees

cruiser202006 wrote: »

Sounds like vessel is in wrong location. If it's before pressure reducing valve/inlet valve then it's not doing anything for the cylinder and it's blowing off on the t&p valve when it's heated up

Bingo - that's what common sense tells me... But I'm not a plumber. The setup is exactly as I described - Mains -> Tank -> Booster pump -> Pressure reducing valve -> Cold water for bathrooms and shower AND Cylinder -> Combination valve (with Mains) -> Hot water for bathrooms and shower. The T&P valve has always leaked when immersion is heated and replacing it hasn't fixed the problem.

K.Flyer

Escapees wrote: »

Bingo - that's what common sense tells me... But I'm not a plumber. The setup is exactly as I described - Mains -> Tank -> Booster pump -> Pressure reducing valve -> Cold water for bathrooms and shower AND Cylinder -> Combination valve (with Mains) -> Hot water for bathrooms and shower. The T&P valve has always leaked when immersion is heated and replacing it hasn't fixed the problem.

The leaking T&P valve is usually a symptom, not the problem, but may need changing as a result of the problem.
Most likely this is a expansion vessel either needing maintenance or to be replaced.
Pressure reducing valve also needs to be checked that it is set correctly.
In an all electric set up another culprit can be the thermostats on the immersions not switching off correctly and causing excessive heat and expansion in the cylinder.
There should be a pressure gauge fitted to the combination valve set up, this also helps to diagnose the problems.

Dtp1979

K.Flyer wrote: »

The leaking T&P valve is usually a symptom, not the problem, but may need changing as a result of the problem.
Most likely this is a expansion vessel either needing maintenance or to be replaced.
Pressure reducing valve also needs to be checked that it is set correctly.
In an all electric set up another culprit can be the thermostats on the immersions not switching off correctly and causing excessive heat and expansion in the cylinder.
There should be a pressure gauge fitted to the combination valve set up, this also helps to diagnose the problems.

+1

Escapees

K.Flyer wrote: »

The leaking T&P valve is usually a symptom, not the problem, but may need changing as a result of the problem.
Most likely this is a expansion vessel either needing maintenance or to be replaced.
Pressure reducing valve also needs to be checked that it is set correctly.
In an all electric set up another culprit can be the thermostats on the immersions not switching off correctly and causing excessive heat and expansion in the cylinder.
There should be a pressure gauge fitted to the combination valve set up, this also helps to diagnose the problems.

Sorry, I forgot to mention the expansion vessel in the setup - it's between the booster pump and the pressure reducing valve. To me, even if it's 100% working, it seems to be on the wrong side of the pressure reducing valve to do its job.

Sure it might help prevent water hammer and also stop the booster pump from starting and stopping as much if there was a small leak, but can't see what use it could be for relieving thermal expansion pressure from the heating of the cylinder.

Out of curiosity, what's the typical pressure setting in a pressure reducing valve for a single story setup? And am I right in thinking the pressure gauge should be read when there is a flow through it - the one here seems to be working fine but usually reads almost 1 bar higher when there is no flow...

K.Flyer

Escapees wrote: »

Sorry, I forgot to mention the expansion vessel in the setup - it's between the booster pump and the pressure reducing valve. To me, even if it's 100% working, it seems to be on the wrong side of the pressure reducing valve to do its job.

Definitely not in the correct position, as has been said in Gary's earlier post. This is why caution is always advised here when working on, or installing unvented cylinders, too many people do not know what they are doing!

Sure it might help prevent water hammer and also stop the booster pump from starting and stopping as much if there was a small leak, but can't see what use it could be for relieving thermal expansion pressure from the heating of the cylinder.

None, as there is a non return valve in the pressure reducing valve.

Out of curiosity, what's the typical pressure setting in a pressure reducing valve for a single story setup? And am I right in thinking the pressure gauge should be read when there is a flow through it - the one here seems to be working fine but usually reads almost 1 bar higher when there is no flow...

They are usually preset at 3 bar, depending on the system, when installing one I might drop it a bit if I have any doubts about existing pipework.
It would read higher because its static and pressurised from the pump, open the tap and the pump works to keep up with demand.
I would be advising that you get a professional in to take a look at things to see what other errors may be lurking.

Escapees

Thanks for the replies - Pressure had been set at 3 bar but I had backed it down to between 1 and 2 to lessen the problem in the short-term! Suspected vessel was in the wrong place but still can't believe someone would go to the bother of putting it in the system but not put it in the right place!

Will get an expert in to sort it out at this stage - it looks like the options are to have the vessel moved to the downstream side of the pressure reducing valve and probably closer to the feed to the tank (it's 30 feet away at mo) or 'maybe' the vessel can be left where it is and a bypass non-return valve put across it (to allow flow from the tank upstream to the vessel) when pressure builds up at cylinder.

K.Flyer

Escapees wrote: »

Will get an expert in to sort it out at this stage - it looks like the options are to have the vessel moved to the downstream side of the pressure reducing valve and probably closer to the feed to the tank (it's 30 feet away at mo) or 'maybe' the vessel can be left where it is and a bypass non-return valve put across it (to allow flow from the tank upstream to the vessel) when pressure builds up at cylinder.

No, don't even go there.
As with all of these things, there is the right way to do things and that ain't it.