Fast drip from Central Heating Overflow

[Bumbly]

The expansion tank in the loft continually pushes water out the overflow when the central heating is on. That means we have a steady stream of water running down the roof.

I have drained and refilled the system several times over the summer to fix leaks, valves etc. Each time I re-filled and tested it, I used to believe that this was just the expansion tank doing its job, allowing the water in the system to expand and overflow.

Now this is still happening, weeks after I last re-filled the system. The ball valve is certainly not leaking - the valve is completely dry and the level in the expansion tank is well below the overflow when the central heating is off.

However, a few minutes after I turn the central heating on, the overflow starts to drip again and continues for as long as the central heating is running.

I am starting to run ot of ideas - is there something wrong with the boiler ?

The system works fine with just the hot water on, no problem at all.

Help please - has anyone got any ideas ?

 

[twgas]

sounds as though you system may be piped wrong and pumping water up the cold feed

 

[fizzput]

Type in 'pumping over' and 'blocked feed' as seperate searches..there's loads of advice there...