Can some one tell me. The water in my cold water tank is geting warm and overflowing, i have checked the ballcock to stop the overflow, ballcock and valve ok could it be a seized up return valve for cold water feed to hot water tank.
I imagine that you have a standard loe pressure set up with cold tank, header tank and hot water tank?
The water in the cold tank will warm, the recent fine weather is probably the culprit. Is the tank insulated? The alternatives, the expansion pipe on the hot water tank or the water in the cold feed to the hot tank conducting the heat back to the cold tank, or a nearby hot water pipe?
Which tank? If its the F&E then Steve is correct. Pumping over can also be caused by blockage at base of feed pipe. In any event don't let it go one because you are shortening the life of your system if you do.
If its the CWST you could have a split coil in the cylinder. Do you have a shower with cylinder hot and mains cold? That can also cause this phenomenon as the cold pushes the hot back into the tank which forces hot water up the expansion pipe into the CWST. This can be dangerous as Steve says.
To Steve the gas: Wouldn't "overpumping" send the warm water to the CH top-up (F&E) tank rather than the cold water storage tank?
To skidman44: Another possibility here is that the heating coil in your hot water cylinder has developed a pinhole leak, allowing water from the CH system into the hot water system and hence hot water up into the cold water tank. I mention this because you said the cold tank is overflowing. If it's this then you would need a new cylinder. AS Steve said, it could simply be that the boiler is overheating the water causing the warm water to go up the expansion pipe into the cold tank. So turning it down may help.