after fitting a reconditioned heat exchanger to a ten year old greenstar 24ri we are still encountering problems with lack of heat in the radiators. the return pipe remains stone cold although plenty of heat to the flow pipe.. we are getting a chirping noise on the pump and the green burn light is on very briefly. this seems to be acting like the old blocked heat exchanger athough it is supposed to be completely refurbished. Prior to this, we have flushed the system removing all radiators and run system with cleaner in on 2 occasions. we changed pump and 3 way switch as a precaution.