WENT TO A JOB 2 WEEKS AGO & TRACED FAULTS TO NO CHARGE IN EXP VESSEL & SEIZED DIVERTER VALVE . FITTED OVERHAUL KIT & PUMPED UP VESSEL. all was ok. today cust phoned & said hot water not getting as hot as it used to. on checking boiler it seems that it is shutting down before the dhw is up to temp. removed ntc connection & dhw hot as stat not cutting in. any thoughts please.