Overflowing Expansion tank advice needed.

[warehouseman]

Am looking after a bungalow where Central Heating & Hot Water has been turned off for about a month. In fact I had turned off water supply at stopcock outside because of heavily dripping taps in kitchen.
Today the taps were replaced. Great, no more dripping. After fitting taps, the water supply was kept on. I came back a few hours later to find an overflow pipe outside dripping quite heavily. Lokoed in the loft, the cold water tank seemed OK, no way near overflowing. The smaller tank is situated quite high up, I presume is the expansion tank. I'm finding it difficult to get to, but putting my hand in at the top it seems very full & I assume this is where the problem is.
Can anyone give us an idea why this has happened. Is it because the water has been off for such a time and a valve somewhere has scaled up? I turned the water off again outside tonight but at the time of leaving , the overflow was still dripping !

 

[Aquazone]

It was probably still dripping as it will take time for the water to leave the tank from the overflow.

I would turn the water off and replace the ball valve in the tank first. If you don't feel comfortable call a plumber, its not a big job.

 

[Reg Man]

Most likely the ballvalve (float Valve). Can be caused by heating circulation, and pipework configuration issues, but as the water has been turned off for some time would look at first option to start with.