We have recently moved into a new house with a traditional open vented heating system. There is an expansion tank in the loft. Recently the ball valve failed so I replaced it.
I have noticed that even when the tank is up to it's normal level there remains a constant trickle into the tank. I cut the supply and left it overnight. In the morning the tank was empty. Did this again the following night and same thing happened.
I left the supply to the tank switched on over the next couple of days and checked it again thinking maybe there was air in the system and that the problem would correct itself but still the same small trickle.
Obviously this leads me to think there is a leak somewhere but I don't think so. All the pipes run in the ground floor ceiling so I think I would have noticed by now if there were a leak.
My only other thoughts are that the water is evaporating somewhere and is being replenished but I can't think why.
Help!