I am having a baxi back boiler gravity fed system changed to a combi condensing system, this will include boiler, new rads, new trv's n lockshields and all pipe work. What should I go for re pipe work, HEP or traditional copper and could the pipe work be done in 22mm instead of 15mm reduced at rads for the trv's etc. Had so much conflicting advice bout HEP, with a new type of sludge appearing in system, but not obviously (mag), any help much appreciated.
stevejo