hot water storage tank overflow

[aero]

I recently noticed that there is water coming out of the overflow on the side of my house. After a bit of inspection, I see that the hot water storage tank is overflowing into the hot water header tank (which now contains extremely hot water). I also see the the ball valve in the header tank is leaking, adding additional cold water to the header tank.

If i fix the ball valve, does that solve my problems? or is there a poblem with the storage tank as well? (i have just moved into the house and there was no problem with the overflow when i moved in, so i suspect that something has deteriorated - probably the ball valve?)

 

[oldie]

Not a plumber so just my 2p's worth
I had the same problem when we moved into this house expansion tank full of very hot water and loft full of steam, it turned out that some time in the 30 years before we purchased the house a cheap hot water conversion had been carried out by installing a direct conversion tube ( or what ever it was called) into the cylinder ( sort of a three flattend tubes joined at top and bottom) instead of replaceing the water cylinder to one with a integral heating coil. to cut a long story down , the flange on bottom of this tube had dropped off allowing the water direct from the boiler to "leak" into the cylinder as it had nowhere to go it went straight up the expansion pipe into the header tank. The cause, either age or corrosion I can't remember, but once the cylinder had been replaced problem solved.
oldie