sounds like a fan venturi or sensor problem .not an expensive job
ex ferroli engineer, July 2011
sounds like blocked plate heat exchanger
could take it out & attempt to clear blockage
tends to be hit & miss
always better to replace for new PHX
would normally replace divertor valve cartridge at same time
only way to guarantee hot water
not an easy job for a beginner
very easy to feel over daunted by procedure
best left for a professional
