Hi,

This problem has me, and 3 different plumbers stumped!

I live in a 2nd floor flat, which is part of a converted Victorian terrace. I have a combi boiler, but I think I have cold water tank (although I can't get access to it).

I went away a couple of months ago, and turned off the water within the flat, stopping all water to the toilet / taps, etc. I came back after a week to find that after 2 days, my flat had started to flood downstairs, starting underneath my bath. About 3 buckets of water came through over the next 5 days till I came back home. As soon as I turned the stopcock back on, the flooding stopped and has not started again!

I have pulled up the floorboards, and all we (the plumbers and I) can find is cold & hot water pipes going to the bath, neither of which are damp.

One of the joists in my bathroom took a long time to dry out, but there is very little evidence of a leak from my bathroom. I haven't taken the ceiling out underneath to investigate (it's an a communal area), but I'm really confused.

I have since found another stopcock in the flat, but this doesn't seem to do anything?

As I can't find the source of the leak, the insurance company doesn't want to know!

Any suggestions gratefully received!

How about, there is a pressure relief valve opening and there is no expansion tank on the water supply. By shutting off the cold water, the expanson of the hot water can't be absorbed by the lines. It opens a pressure relief valve somewhere and you have a flood.

From what you describe this could be many things including bad roof flashing. Has is rained when this leak took place? Is there a 3rd floor above you?

Thank you for your replies. To answer Ball's question, there is another flat above me, and there has been a lot (!) of rain since then this summer, so I'm sure it's not rainfall which caused the problem.

Re: KeepIt's thinking, are pressure valves like that usual in plumbing systems?

Thanks,

Any hot water system has to have a pressure relief valve. Even a simple electric or gas hot water heater.

If a tstat failed closed, the water temperature and pressure would get too high and the tank could burst.

Here is a good link:
Water Heater Pressure Relief Valve