ferroli hot water and central heating problem luke warm rads

[boris6760]

i have a 3 year old ferroli maxima 35c my problem first started a week ago when my shower would hot then cold then hot then cold and now my radiators are only luke warm the boiler keeps starting up and then shuts down it is as if it thinks the heating is up to temp and then stops then knows the water on the heating needs heating up comes on again then stops again .my hot water from the taps runs hots then cold hot the cold ?? any ideas maybe senors prob or printed circuit board i need some help

 

[picasso]

sounds like a stuck diverter valve.

 

[Paigntonplumbers]

If its just hot water that goes hot cold hot cold almost certainly heat exchanger blocked as the boiler overheats turns flame off then cools down quick and comes on again. If it does it in ch mode as well could be pump not working properly to dissipate the heat and shutting down. It is a ferroli though and their awful so it could be all sorts.
Hope this helps