What is the problem when:-?

they have a dual pass set up heat exchanger rather than a dhw plate so my guess would be heat exchanger shot.
hoses rot and leak on them too

iain
June 2008

the expansion vessel is either undercharged (needs to be charged to min 0.5 bar for 5m head) or else it has perished and will need replacing.

if charge is ok, and when air is released no water comes out, you may have another possible fault, that will require replacing the dhw heat exchanger (secondary water passing into primary water across the heat exchanger)

T
June 2008