"Patb" wrote in message
ups.com...
After replacing the ball valve, thinking that was leaking and causing
the overflow to go, I have just realised that warm water is coming up
from the immersion in the bedroom up into the loft tank.
Grateful for advice on what I should do to stop this,
thanks

If the cylinder is heated indirectly from your boiler then it is most likely
that the primary water coil is perforated.
Only option is to replace the cylinder.