Cold water&EF Cistern

[Alireza]

Lately the over flow from my cold-water cistern in roof space start leaking
I have check the Ball Valve and is not due to faulty Valve
The water in thank seem quite worm for this time of the year and I have seen water drip from the pipe which is coming from the top of the hot water cylinder and hangs just above the cold water Cistern (vent ppe)
While in roof I noticed that the water in Feed and expansion Cistern is very hot
My boiler is not that old ( 4yreas) and has been serviced every year
I have a Two-Circuit System
Any help

 

[75pete]

Just how hot is the hot water when you turn on the tap. Its sounds like your hot water cylinder is venting hot water into the cold tank.
Check the cyl. stat
Check the immersion if the cylinder has one
Check the 3way valve for operation if your system has one

 

[Alireza]

Thanks 75pete for Speedy reply
The water from Hot water tap is hot as it used to be and the cold is cold 1
The Cyl stat is set at 60
The electric Immersion for Cyl is off
How do I check the 3way Valve ?
There are no problem with heating and hot water
The pump is set at 2