Dripping Expansion Tank - Please confirm diagnosis!

[CutAndPaste]

Hi,

I've got an oil fired Central Heating system and the overflow pipe drips intermittently. There's a blue expansion chamber just above the overflow that sounds 'full' (compared to the red one that sounds empty. In other systems I've had, when this blue expansion tank was full of water, it meant that the diaphragm is broken and I need a new expansion chamber

Does this sound right?
Cheers.

 

[Marc Bowers]

Not necessarily, like a car tyre, it could be punctured and needs replacing or the valve might be letting by so it needs pumping up again and the valve checking to see if it is holding or needs replacing.
A bit of spit over the end of the valve will soon tell you if the valve is letting by, and although replacement of the valve needs a specialist tool, its usually cheap and available at most motor spares retailers.