Temperature relief unvented cylinder

[Matt0029]

What can be causing a temperature relief to drip. I have recharged the expansion vessle that had totally lost its charge. I am g3 registered. Thanks

 

[SJB060685]

You sure you mean the combined temperature and pressure relief valve? The 7 bar 95°c one?
Is it fed by immersion or boiler?
It's most likely a bit of crap stopping the valve from seating properly. Of course it could be sensing excess temperature and that needs investigatin
Its probably not pressure related because the 6 bar expansion relief valve on incoming main should activate first, unless that's faulty. If that's the case you'd need to investigate why the incoming pressure has risen ie, faulty pressure reducing valve etc.

 

[Matt0029]

You sure you mean the combined temperature and pressure relief valve? The 7 bar 95°c one?
Is it fed by immersion or boiler?
It's most likely a bit of crap stopping the valve from seating properly. Of course it could be sensing excess temperature and that needs investigatin
Its probably not pressure related because the 6 bar expansion relief valve on incoming main should activate first, unless that's faulty. If that's the case you'd need to investigate why the incoming pressure has risen ie, faulty pressure reducing valve etc.

Thank you I have just taken them apart it's the 6bar expansion relief valve on the incoming main that's letting by have recharged expansion vessel and is still letting by. Its a direct cylinder.

 

[SJB060685]

Ok. If that's the valve and its dripping all the time, not just when heating I'd suspect a bit of crap stopping it from seating properly (manually open valve and discharge some water to see if that shifts anything). If not that then the the pressure reducing valve may have failed. If theres any mixer taps or showers then you could have a back feed problem sending excessive high pressure cold water back into HW side.
If it's only doing it when heating the water then the expansion vessel could be at fault, possibly a couple of the above at same time.

 

[Matt0029]

Discharging water from it doesn't cure. Could it still be dirt? Expansion vessel is OK. And so is pressure reducer.

 

[SJB060685]

Crap can and has caused this but usually flushing through would dislodge debris. Any doubts just isolate supply and take off and have a look. I suspect though that if the vessel is sound and of right size and reducing valve is ok then your problem lies elsewhere

 

[Matt0029]

Crap can and has caused this but usually flushing through would dislodge debris. Any doubts just isolate supply and take off and have a look. I suspect though that if the vessel is sound and of right size and reducing valve is ok then your problem lies elsewhere

Thanks the expansion vessel was totally empty when I got here. I have recharged and is still dripping. Do they sometimes not reseal correctly when discharged?

 

[SJB060685]

Are you a 100% sure the vessel hasn't failed? Have you tried dropping the pressure slightly through nipple to see if water appears or air? The vessel as you know is just a rubber diaphragm filled with air and no water should escape from nipple unless the diaphragm had ruptured. Also when you recharged the vessel did you drop the pressure out of the system first?

 

[Matt0029]

Are you a 100% sure the vessel hasn't failed? Have you tried dropping the pressure slightly through nipple to see if water appears or air? The vessel as you know is just a rubber diaphragm filled with air and no water should escape from nipple unless the diaphragm had ruptured. Also when you recharged the vessel did you drop the pressure out of the system first?

I did yes. I dropped pressure and took expansion vessel off as couldn't reach it in place.
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Vessel hasn't ruptured

 

[SJB060685]

Ok. So if the pressure reducing valve is sound, vessel is sound and relief valve is still dripping I'd check to see if there is a back feed. Isolate inlet cold valve to cylinder, drop pressure out of the system until dripping stops and then leave for 5-10 minutes. If after a period of time the dripping starts again you know you have back feed from somewhere

 

[Matt0029]

Thanks I have done that and it didn't start re-driping

 

[SJB060685]

Ok if that didn't start dripping after enough time for the pressure to build up again then we can rule that out. Now I would be most suspicious of either the PRV failed or the pressure reducing valve. Just out of curiosity what static pressure is the cold mains to rest of house?

 

[ShaunCorbs]

What’s the main incoming pressure could be back pressuring

 

[Matt0029]

What’s the main incoming pressure could be back pressuring

Its high around 8 bar.

 

[SJB060685]

What’s the main incoming pressure could be back pressuring

Do you mean feedback which is what we've discussed above?

 

[ShaunCorbs]

Do you mean feedback which is what we've discussed above?

yea I would see what the pressure is in the unvented cylinder

 

[SJB060685]

Yes I've had him test this and apparently all good.

 

[Matt0029]

Do you mean feed back through a tap? There's one tap, the kitchen tap that has mains pressure one side and 3.5 bar hot water on the other. It's a dual flow tap though. I think.

 

[SJB060685]

Yes that's what hes suggesting and what I had you test for earlier

 

[Matt0029]

Yes that's what hes suggesting and what I had you test for earlier

Thanks I think my next step would be to swap the composite valve then.

 

[SJB060685]

Thanks I think my next step would be to swap the composite valve then.

The pressure relief valve and or combination valve pressure reducing is my suspicion. I've tried covering everything with you in the hope it only requires one return visit for you

 

[ShaunCorbs]

Do you mean feed back through a tap? There's one tap, the kitchen tap that has mains pressure one side and 3.5 bar hot water on the other. It's a dual flow tap though. I think.

this one got a dcv on the hot side ?

 

[Matt0029]

Yes thanks very much for your help.
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this one got a dcv on the hot side ?

It hasn't no

 

[ShaunCorbs]

Yes thanks very much for your help.
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It hasn't no

I would fit one and see

 

[Matt0029]

I would fit one and see

I may put a pressure reducer on the main in coming pipe and set to 3.5bar. So it's balanced everywhere.

 

[SJB060685]

I would fit one and see

Shaun I advised to isolate cold main into cylinder, drop some pressure out and then see if the PRV started to drip again after enough time for any back feeding to accumulate and it didn't happen, so installing a double check valve is not needed to test correct?
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I may put a pressure reducer on the main in coming pipe and set to 3.5bar. So it's balanced everywhere.

I would advise one under the kitchen sink on incoming main so as you say it's all balanced, although this is not the current problem

 

[ShaunCorbs]

Shaun I advised to isolate cold main into cylinder, drop some pressure out and then see if the PRV started to drip again after enough time for any back feeding to accumulate and it didn't happen, so installing a double check valve is not needed to test correct?
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I would advise one under the kitchen sink on incoming main so as you say it's all balanced, although this is not the current problem

might of caused the original problem tho me and you know they don’t seal good after they’ve discharged

I would say prv on incoming one size larger eg 28mm for a 22mm supply etc

and change the incoming block

 

[EvilDrPorkChop]

I've never had any issues with them sealing after opening - it's clean water, in theory no rubbish should get under them and thus seal OK.

I've only ever had three fail (where the Expansion has been OK) has been on temperature. One dripped on temperature rise and the other two would open full bore on a temp above 45oc. The other issue is backflow but that seems to have already been discussed.

Daft question - but are you sure it's the Temp/Pressure Relief valve dripping. Many installers tee that in with the blow off from the combination valve before the tundish - could it be this dripping instead? I find more regularly these fail.

 

[SJB060685]

I've never had any issues with them sealing after opening - it's clean water, in theory no rubbish should get under them and thus seal OK.

I've only ever had three fail (where the Expansion has been OK) has been on temperature. One dripped on temperature rise and the other two would open full bore on a temp above 45oc. The other issue is backflow but that seems to have already been discussed.

Daft question - but are you sure it's the Temp/Pressure Relief valve dripping. Many installers tee that in with the blow off from the combination valve before the tundish - could it be this dripping instead? I find more regularly these fail.

It's the 6 bar expansion relief valve that's the culprit, not the combined pressure and temperature valve mate

 

[EvilDrPorkChop]

It's the 6 bar expansion relief valve that's the culprit, not the combined pressure and temperature valve mate

Ah yes, I read the first post and skim read the rest!

I'd put it down to a faulty 6 bar blow off then, easy enough to replace without replacing the whole combination valve. Had plenty of them fail for no apparent reason, probably most likely from the expansion not working correctly previously.

 

[moonlight]

I you sure its not the cold letting by? pressure reducing valve