Hi, Greenstar CDi combi boiler 3 years old. Top floor radiators cold so bled, this dropped water pressure to zero so recharged back to 1.2 bar and system working fine. Then started to overheat intermittently when turning on tap for hot water (when heating is running). Led display rises rapidly form 60,70,80 etc until it tops out at u9 (which means 109 as only 2 digit display).

System then cools and is OK, the next day the same thing will happen. Any ideas?

Graham, January 2013

When hot tap is opened / turned on (with heating already on) boiler temp rises to over 100 degrees so shuts down.

Graham, February 2013

does it happen when the hot waters running or when u close the hot water tap. also does it only happen when the heatings on.
check the pump has been bleed and its working fine. if u respond i can help u diagnose ty

kash, January 2013