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We have a back boiler serviced every year a Baxi it kettles 24/7 from start till it gets fully hot say 2-3 hours ? we have fernox in the system flushed it but no good we canot get rid of the noise? CAN any one help me out and pos tel me how or what is causing the problem

Many thanks

Limescale, a build up over many years in the heat exchanger, pipework and tank/cylinder, probably too old and too stubborn for descaler to dissolve.

New heat-ex and pipework required. Weigh up the costs - likelihood of other faults ? time for a boiler/system upgrade maybe ?