If you can see water entering the tank, does it stop when you turn off the
water mains stopcock ? If not then the water must be due to expansion
(i.e. it's getting hotter) but if so then a mixer valve is possible. Are
there service valves near these you can isolate them with ?


(not easy to isolate it for 24 hours as the tenants use the shower often).

Not students then :-)


Great idea G&M. I will try and get over to the property this afternoon
and check. Yes, you're right - they are aren't students ! ;-)

Many thanks for reading this and replying - much appreciated.

Peter