Strange overflow/back flow problem.

[keasy]

Hi, i'm hoping someone can offer me some advice.


For the past two weeks my cold water storage tank in the loft has been over flowing. First thing was first and I checked the ball cock/valve bent the rod etc. But it didn't resolve.
So I ended up buying a new ball cock and valve. Problem still persisted.
Strange.
So I have eventually managed to detect that the excess water is weirdly coming from the bathroom cold water feed pipe. How I do not know.
I closed the main valve and marked the water level then closed the gate valve on the feed to the bathroom and next morning the water level was the same.
The next night I closed the main again, marked the water level and left the gate valve open on the bathroom feed and as I expected the water level was up, in fact to the overflow pipe.

i'm really baffled as to how it can be happening, as far as I know there is no cross over anywhere and the rate of the excess waters flow is not high enough to make me think it's from a cross over to the main.

A solution is to take the cold water storage tank out of the loop all together and get my bathroom connected to the main. But that would probably involve ripping out the boxed parts in my kitchen and breaking of tiles in my lovely bathroom

Does anyone have any ideas as to where or how this water is getting to the bathroom feed and into the cold water tank ?

Thanks.

 

[buck51]

The check valves on your bath thermostatic mixer are passing!!!

 

[keasy]

K, thanks for replying mate I appreciate it.

Are the check valves replaceable or would I be looking at buying a new mixer ?
My dad and myself thought it could be something to do with the baths taps btw

 

[buck51]

You can usualy take them out and clean them, there will be cr@p under the seat
It would be better if you flush hot and cold pipework out if not it could happen again and again

 

[ChrisR]

It probably isn't a thermostatic mixer that's doing it.
More likely is the basin tap, as that may have mains one side and hot the other whereas a shower or other thermostatic mixer shouldn't.

You might have non-return(check) valves which are passing, but on basin taps there often aren't any.
Water can pass from high to low pressure either through porous brass castings, or past rubber seals which , er, don't any more.
Taps like that should have double check valves in the pipes which supply them, which is usually a quick addition. They need to go in both pipes, one to protect your loft tank, one to protect the mains supply.