Ferroli 102 DHW intermittent?

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.

arbee.
February 2008