Unvented Cylinder Dripping into tundish

[pthawkes]

Hello,

We have an unvented Ariston cylinder. When the boiler kicks in to heat the water, one of either the TRV or PRV is passing water. The water that is passed is cool so I'm suspecting that its the Pressure relief valve connected to the Expansion Vessel. I know the EV is discharged. I have read somewhere that this will cause the passing of water at the prv. My problem is that I cannot charge the EV. I have tried to pump it with an electric pump and with a hand pump, but the air just won't go into the EV.

Is there something I'm missing or is the EV broken? Has anybody else experienced similar behaviour. Also why would a discharged EV cause the prv to pass water when the boiler kicks in to heat the water.

Many Thanks in advance!

 

[gas4you]

Are you trying to pump it up with it drained of water?

See FAQs on repressurising an expansion vessel.

 

[Agile]

You need to determine the working pressure of the cylinder, ideally be measurement, but from the data plate perhaps if you cannot measure it. Usually about 2.5 Bar.

Then turn off the supply to the cylinder and open a hot water tap to remove all pressure from the cylinder.

Next measure the air pressure in the EV, usually with a foot pump gauge, and pump it up if necessary.

The spec usually asks for a pre-charge in the EV about equal to the working pressure! Some foot pumps are struggling to produce this pressure. In theory you can remove the EV to enable you to use the foot pump on the floor rather that by hand.

Tony

 

[sooey]

The spec usually asks for a pre-charge in the EV about equal to the working pressure! Some foot pumps are struggling to produce this pressure. In theory you can remove the EV to enable you to use the foot pump on the floor rather that by hand.

Watch out Tony, people will be thinking that you can't get your leg over.

 

[pthawkes]

Thanks, I have looked at the FAQs, am a bit confused as I have two EV/PVs one for the Heating system which is red( I think this is the one referred to in the FAQs) and this one has a pressure guage and I charge it with water from a filling loop.

Its the other EV which is white which needs charging with the bike pump. I will attempt to pump up using agiles advice. Thanks again.

Could anyone explain why this causes the PRV to pass water?
Thanks again!

 

[Agile]

When the cylinder is cold it fills to the set pressure on the reducing valve.

When it warms up the water expands and that expansion is absorbed by the EV if the air charge is pressent and correct.

If the Ev is not working then the pressure rises and on most systems there is a 6 Bar PRV at the cold inlet which opens to relieve that pressure.

On all systems there is a second safety device which is a combined pressure and temperature relief valve. This is normally set to open at 90° or about 9 Bar.

Tony

 

[pthawkes]

Thanks Tony it makes sense now.

Moderator 10.
I have had 2 Certified plumbers look at my system and both have failed to pump the PV...I have watched both and neither of them attempted Agile's suggestion.
This is the reason I have come to this forum and as a result have established what my problem may be.

Thanks again!