Unvented cylinder leak. Experts only - is anything wrong? (Ed.)

[Johntheo5]

I'm almost certain the back pressure is the problem. After doing a bit more research I have a hissing tap and no non return valves fitted on the mixers. Is the hissing tap the faulty mixer or could that just be a symptom?

If you run that tap on HW only for a minute or two. then shut it, feel the hot supply underneath the tap (if possible), it should quickly cool down if the mixer is passing. Do the same test with any other accessable mixer pipes.

After a plumber flooded my kitchen from.the main 3 times I'm reluctant to fit a prv under the kitchen sink. I'm guessing that's my only option as there's no room between the mains isolator outside and my house.

Could I fit a non return valve on the hot water discharge at the cylinder?

Installing a NRV should be OK IMO, may require a G3?.

Thank you for all your help, I really feel like you've gotten to the bottom of this issue which has cost me too much money already.

 

[alwaysproblems]

Top man, thank you

 

[Madrab]

Is the hissing tap the faulty mixer or could that just be a symptom?

The hissing tap would probably be a symptom of the mains being too high and the valve has started to let by, could it also be getting by the hot side too - yes, a distinct possibility.

Could I fit a non return valve on the hot water discharge at the cylinder?

Wouldn't usually have any type of valve on the outlet of an unvented, even an isolation - it's never specified as a standard in any MI's etc

Whether it's actually to the regs or not is something I'd need to check back on as I can't remember it ever coming up as it usually isn't needed. If anywhere, check valves would usually be installed at the outlet ends.

This only treats the symptoms though and if the check valve fails then it's back to square 1 - the cold mains need to be reigned in or the cold supply to all the outlets needs to be connected to the balanced outlet of the UV.