Unvented direct cylinder

[callum84]

Hi
I have recently had an unvented direct cylinder fitted by a g3 qualified person - however there seems to be an issue that is hard to get to the bottom of.

when the lower immersion is on for about 1 hour - the discharge pipe starts to drip cold/cool water.

the installer identified this as the pressure reducing valve, and tested the expansion vessel which was factory set at 3.7 bar.

The mains pressure into the property is 2.5 bar - and the suggestion was to get the expansion vessel set at 2.5 bar also to see if this works.

the dripping only seems to be evident when the main immersion is on for an hour or so

This seems to be a trouble shooting issue , with back pressure , check valves , balanced pressures and NRVs all being mentioned as potential resolutions.

Does anyone have any similar issues as above and any ideas what can be done to resolve?

the discharge isn’t a lot - just a fairly constant drip.

Any constructive info or suggestions I can pass on to the installer would be greatly received for my own piece of mind.

best regards

 

[Gasguru]

Make and model of cylinder and photos/diagram of the installation...the problem is likely to be incorrect installation...expansion safety valves are often set at 6 bar so something's very wrong.
If the installer can't solve it he's not up to the job...these things are pretty simple.
I bet he hasn't even had the nous to plumb in a few gauges/valves to monitor where the problem lies.

 

[Madrab]

Must agree .... if he is actually a qualified G3/UVHW installer then he should be able to troubleshoot an new installation (especially his own) without breaking a sweat. As suggested, there isn't much that is difficult about troubleshooting these cylinders, when qualified.

He shouldn't be thinking about nrv's/back pressure/balanced supplies etc at this stage, that should all have been sorted out before the install began. That being said if the mains is at 2.5bar then none of that should really be an issue, especially if it only occurs when the cylinder is being heated.

 

[callum84]

Mad rab it’s only when the cylinder is heating using the main immersion - when the boost immersion is used there is no dripping. Do you have any ideas what the issue could be?

 

[Gasguru]

When you heat the whole cylinder using the lower element there is more expansion of water to accommodate....
Post some pics then we'll get an idea of whether you bin the installer or persevere.

 

[Madrab]

OP ... as @Gasguru suggest, the main element is heating the whole cylinder so a lot more expansion needs to be absorbed, which looks like it isn't being if it's opening a release valve.

As also suggested, make and model and some pics will help enormously.

 

[Quaintruler]

I had an issue with an unvented H/W cylinder a while back, where the temp and pressure relief valve was letting by into the tundish and out to waste most of the time. And on a water meter, it makes you want to do something about it. My unvented was only being heated by the boiler though, and no immersions were in use. I called a heating engineer and he reckoned the expansion vessel was probably undersized. There are calculations to determine this of course. Anyway, slightly larger expansion vessel now in place, and the system has been as good as gold for at least 2 years now. At service intervals the expansion vessel has needed a small amount of charging though.