"Roger Mills" wrote in message
...
In an earlier contribution to this discussion,
Denny wrote:

I assume that you have 2 tanks in your attic - a large cold water header
tank for the HW system, and a smaller fill and expansion tank for the
primary circuit? I assume that it's this smaller tank with which you have
the problem? I assume further that the water level in the large cold
header tank is higher than that in the small F&E tank?

If these assumptions are correct, I fear that you need a new hot water
cylinder. The HW cylinder has an internal coil/heat exchanger through
which water heated by the boiler passes, heating the domestic hot water
without mixing with it. BUT, if this coil springs a leak, the primary and
secondary circuits *do* mix - causing water from the higher tank to flow
into the lower tank.
--
Cheers,
Roger


All your assumptions are correct - Thanks for the clear explanation Roger