My 102 is about 7yrs old. Long been a problem with DHW cycling between hot and cold a nuisance in the shower. Thermistors have been changed, PCB as been changed. Now the boiler will shut down when providing DHW, sometimes requires a reset, sometimes will come OK after time. The whole thing appears to be unpredictable. My service firm have made 7-8 visits in the last month and dont seem to understand the problem.
If the problem only happens with hot water, it is probably the flue fan venturi either cracked or brittle, or the fan impellor is dirty causing insufficient air flow to operate the air pressure switch.
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