Suspected Leak in Hot Water system vs Cylinder behaviour?

[John.g]

Unless you can shut off the hot water outlet at the cylinder then you don't really know if the hot water is leaking back through the mains via a mixer, when the stopcock is shut then obviously can't/wouldn't be able to leak back. With no usage, the hot will be higher than the mains and higher still with cold water usage but no hot water usage.

 

[stormyuk]

A leak of a litre or more a day into the fabric of a building should be quite noticeable if it continues for a few days.

Based on your observations, I suspect that the PRV is most likely to be responsible. You could confirm this by connecting a pressure gauge to the DHW and see how it correlates with your 'leak'. The mains inlet pressure should also be checked. PRVs need to have a reasonable drop across them to work correctly. If the incoming pressure is not high enough, e.g. because all your neighbours are having their baths and showers, then the cylinder will be left at too low a pressure and will top up once the inlet pressure rises again.

You do sometimes get leaks that are temperature sensitive, e.g. open after hot water has been run due to the increased temperature and close as the pipework cools, but they are not common. And, as I said above, a litre a day from your DHW is probably going to be fairly obvious once you start looking.

Believe me, I have looked for the leak and its probably been doing it a long time now (since the house was built or potentially when the PRV was changed with the old faulty tank), it just I only just noticed it when I happened to be looking at the meter one day.

For now I think I will just keep an eye on it, as getting a plumber to do all that work checking or changing the PRV (in case) is probably going to cost more than the water I am "losing".

Annoying for sure although if what John suggests below is whats happening I might have bigger issues....

Unless you can shut off the hot water outlet at the cylinder then you don't really know if the hot water is leaking back through the mains via a mixer, when the stopcock is shut then obviously can't/wouldn't be able to leak back. With no usage, the hot will be higher than the mains and higher still with cold water usage but no hot water usage.

Unfortunately there seems no way to do this, the hot water feed off the tank is just piped with no stop valve etc.

If it is what you suggest I am not sure there is an easy fix as its gonna be neigh on impossible to retro fit a balanced cold feed to every mixer without some serious intervention (2 showers, one bath, and 5 other mixer taps upstairs and down).

Thanks for the responses.

 

[Ben-gee]

The reason I asked about a balanced cold after the hot shut off is that I suspected the leak would be in a toilet - as 90% on ‘unnoticed’ leaks are, usually flush valve letting by and then fill valve making up.
But sounds like nit in your case if isolatingonly the cylinder stopped the leak.

 

[Timmy D]

Just FYI, unvented cylinders shouldn’t have a hot outlet isolation valve (just in case you’re thinking of adding one).

 

[stormyuk]

Unless you can shut off the hot water outlet at the cylinder then you don't really know if the hot water is leaking back through the mains via a mixer, when the stopcock is shut then obviously can't/wouldn't be able to leak back. With no usage, the hot will be higher than the mains and higher still with cold water usage but no hot water usage.

Do water meters not run backwards?

Would the pressure really be enough to push water back past the meter?

Just FYI, unvented cylinders shouldn’t have a hot outlet isolation valve (just in case you’re thinking of adding one).

To be honest I wouldn't be messing about like that to test a theory.

Even doing all the pressure measurements suggested is beyond me. I am an electrical engineer not a heating and plumbing engineer. I'd get someone in. Just not sure it's worth it for the amount of water I am losing. It would be nice if I could get a full 24 hour measurement of how much water I am actually losing. Asking two girls to not use water for 8 to 9 hours is a stretch!

I am just trying to get down to the bottom of the system behaviour and if there is something I can do about it without ripping the fabric of the house apart.

I am pretty sure I don't have a physical leak somewhere considering I should be able to find some evidence of it. But, still it's a worry in the back of my mind.

Of course wasting water is never good either for the environment or my wallet.

If the problem is actually the lack of a balanced cold or something else. Why I asked the original question.

The builder who built this house seems to do this on all their homes so I am surprised more people have had issues..

Thanks

 

[John.g]

It can certainly flow backwards against the mains if the pressure is higher but whether it would turn the meter in reverse or not, don't know.

Have you got a pressure gauge mounted anywhere after the NRV?, say on the cylinder itself?, if you have, then as the cylinder is cooling down and with no usage the pressure should start falling, if it doesn't then it points to the PRV increasing its downstream pressure.
Wthe temperature falls from 60C to 50C then the pressure would have to rise by ~ 0.4bar to increase the water volume by 1.85 litres (per meter reading).

 

[moonlight]

Is the pressure relief valve dripping into the tundish when heating the water?

 

[king of pipes]

If the water meter stops when the isolation valve on the combination valve is closed and no water is being used in the property? then this points to a leak you have tempreture and pressure relief valves fitted to the cylinder I would be monitoring these especially at heat up times do you have any idea what your incoming
water pressure is ? water pressure can certainly rise over night and a faulty combination valve is quite possible, your cylinder is still under warranty but you must determine what and where the problem is and where you losing water . Kop

 

[John.g]

IMO, a pressure gauge is the first requirement to track down the problem.

What we havn't mentioned is a holed heating coil but if the heating system is sealed then eventually if the cylinder pressure is consistently higher than the coil pressure then the PRV will eventually lift on the boiler, however if the two pressures are very close and at times the cylinder pressure may be lower than the coil pressure, in this case water will be shunted back into the cylinder thus keeping a balance.
If the boiler& system is open vented then eventually the F&E tank should start overflowing.

 

[stormyuk]

Is the pressure relief valve dripping into the tundish when heating the water?

No the tundish is dry it dripped a little bit for a day after I recharged the air gap but, since then it's been fine.