Cold Water Tank overflowing

[Chris15]

Help, I have a problem with my Cold water tank overflowing in the roof, it isn't the valve as iv'e replaced it twice but gradually fills up doing the day and overflows, I think its coming from the expansion pipe but its only started doing it recently, I have competely drained the cylinder and refilled but it still does it, my cylinder has 2 Immersion heaters but the bottom one is u/s so we just use the booster one, is that the reason
Also when it overflows it is not just dripping but running water,
Thanks Chris

 

[JohnD]

Is your hot water cylinder also heated by a central heating boiler? (Or has it been in the past?)

The problem is not caused by the immersion heater.

 

[Chris15]

Hi John, The Cylinder is just for hot water, we have no boilers in the house ( all electric ) I cant understand why theres so much water, I have set the valve to its lowest setting which is about 18" below the overflow pipe, overnight it fills up and overflows, I have placed a bucket under the overflow and that is full also, that seems like to much water even for expansion, I have tried a brass valve and also a plastice valve ( twice ) in case its the valve, its as though its got another supply from elswhere!

 

[JohnD]

h'mmm, not what I thought then.

Is there a service valve/stopcock on the supply to the tank? This would verify that there was not a running floatvalve or connecting joint.

As you say the water is running out I imgine you would notice if the float valve was dripping that badly.

Do you have any mixer showers or bidets? Do they have service valves you can turn off?

 

[Chris15]

Hi John, There is a service valve on the cold feed and I have tried turning this off a night, also I have a shower with the cold feed from the tank and the hot from the cylinder which has stop valve on it, it all seems to point to the tank valve but iv'e checked it several time and it doesn't seem to be leaking, but I do have a mixer valve on the Bath and sink that are connected to the mains supply, is it possible that the cold water is backing up the hot pipe to the cylinder or tank!

 

[bster]

not if the hot tap is closed

 

[Chris15]

Well thanks to JohnD the fault was a mixer tap on the bathroom sink, the cold mains water was leaching in to the hot system and constantly filling the hot tank, when I put my ear next to the mixer you could hear water running! Have replaced mixer with a new tap with 2 taps instead of the one and have cured problem.
Many thanks