This can only be a leak somewhere on DHW right?

[WaterTight]

Customer goes away for 2 weeks and turns off water. When they come back and turn it on CWSC fills up for 5 minutes. CWSC just feeds cylinder which in turn feeds kitchen, basin and bath hot. No visible leaks. CWSC in good condition, no leaks, has a lid.

Must be leak on hot somewhere hidden right?

 

[WaterTight]

I've just thought actually they said they never went up to actually look, they just heard it, so theoritcally it could be the f+e they are hearing...

 

[oz-plumber]

Was the HW cylinder left on for the time they were away.

Could just be evaporation, if so.

Could also be as simple as a dripping tap

 

[Howsie]

I've just thought actually they said they never went up to actually look, they just heard it, so theoritcally it could be the f+e they are hearing...

More likely!

 

[WaterTight]

Was the HW cylinder left on for the time they were away.

Could just be evaporation, if so.

Could also be as simple as a dripping tap

No, turned off.

No taps drip.

More likely!

Why more likely the f+e?

 

[Howsie]

More than likely a leak from the CH under the floor somewhere.