Pressurised hot water cylinder venting

We've got a ~10 months old Joule pressurised 200 litre hot water cylinder, replacing a 25 year old cylinder. It is protected with two pressure valves (3 bar I believe) that join via a "Y" shaped pipe then drain through a little "open" bit (a tundish?) down to a powerful pump that scoots water up, along through the loft, through the wall and down a pipe on the outside of the wall. There's a fraction of a cupful of water thrown out each time.

It's been fine (pump never ran) until last week. It's started running for ~ 5 seconds once a day, now up to twice a day. Looking in the side of the tundish, I can see occasional drips coming down.

We'll have the system serviced by the same installer in a few weeks time. In the meantime the powerful pump starting up and snorting the water out like some kind of angry baby dragon in the small hours of the morning is super annoying. I assume there's nothing I can do as an unqualified householder?

What model Joule do you have, 3.0bar seems very low for the expansion relief valve setting, is the pump just used to pump the water in the tundish to the outside?.

Johntheo5 said:

What model Joule do you have, 3.0bar seems very low for the expansion relief valve setting, is the pump just used to pump the water in the tundish to the outside?.

Click to expand...

You're correct. The inlet pressure is marked as 3.0 bar, but the relief valves are labelled as 8.0 bar and 10.0 bar.

Model 200L Cyclone Air Indirect.

Yes, the pump expels water in the tundish to the outside. I think it was the only option for routing the exhaust water.

This UV cylinder seems to have a air bubble internally to take up the expansion vis a external expansion vessel, its more than likely that the bubble requires re establishing, it can be done by the householder and normally the method is labelled on the cylinder itself or in the MIs, basically, you shut off the cold water supply + immersion heaters, open any HW tap that is lower than the cylinder, when the HW stops flowing, open the T&PRV (temperature and pressure relief valve) mounted high up on the cylinder, when water stops flowing from this, close it, then close the HW tap and reopen the cold water supply.

Thank you. I found the procedure in the manual for the cylinder and followed it just now. It took in a fair amount of air so that's probably vanquished the dragon for a while.

10 months is probably a fairly normal time between recharging, if you think of it, you have ~ a 50L (25%) air bubble when you start filling the cylinder, this becomes a 12.5L bubble at 3bar and on reheating to 60C, becomes a 9.5L bubble with a cylinder pressure of 4.3bar, the PRV lifts at 8 bar so that bubble will have lost ~ 7.0L to become a 2.5L bubble and each time you do a full reheat the PRV will eject ~ 0.5L of water or 0.25L on a half cylinder reheat if the PRV reseats at 7.0bar.,

Of course, someone, some day, will come up with the truly brilliant idea of actually installing a pressure gauge on a unvented cylinder which I think is a pressure vessel!!.