Problem with ferroli domicompact

[top plumber]

I have a problem with my boiler in my house its a ferroli domicompact f30 b, whilst running hot water it will run hot for a few minutes and go cold for a few seconds and go hot again it repeats this cycle at all dhw outlets any ideas im an installer so dont know really where to start??

 

[quality]

Sounds like a scaled up PEX

 

[top plumber]

scaled up pex? where to start? sorry for being igronant just havent a clue when it comes to inside the boiler, i dont live in a hard water area aswell?

 

[quality]

Pm dan and get in the gas safe forum you get all the answers you need