My home central heating system uses a combi boiler (Brittony Combi
80). I think the secondary heat exchanger is starting to get blocked
because the heat and flow rate of the domestic hot water is becoming a
little erratic. I understand the hot tapwater is heated by the central
heating water via the secondary heat exchanger. Rather than just
remove the secondary heat exchanger and addempting to desludge it, I'm
wondering if it would make more sense to desludge the whole central
heating system. I'm thinking that if I desludge the whole system,
then the secondary heat exhanger will get desludged in the process
(apart from the channels that the mains water flows through, of
course, which is probably clear anyway. Anyone agree?

I did the desludge process about three years ago, using a Fernox
desludge solution. I left the stuff in the system for a couple of days
then flushed it out and refilled with fresh water plus the standard
Fernox additive. Should it need doing again by now?

Many thanks for any advice.

Don