pro combi he overheating

[crewpad]

hi everybody.
i have a pro combi he boiler(2 and a bit yrs old..... just out of warrenty) the hot water is working fine. when i turn on the central heating it runs fine for a while then goes into " temporay fault"----green flashing light, then refires for about 2 mins.. it does this 4 or 5 times then i get a solid red light- overheated. if i shut the system off for 5 mins then turn it on again it starts all over again. the wierd thing is the hot water is working fine.
any help would be great as im starting to lose my hair. thanks in advance.

 

[Boilerman2]

CH Thermistor fault?
However you have to gain entry to the combustion box to work on this so its a job for a Gas Engineer