Problem with Ideal Isar Combi boiler?

I have an Ideal isar combi boiler running off a seperate thermostat. All has been fine with it until now.
The boiler is firing up the central heating several times during the day although the stat isn't calling for it to do so.
The manual isn't too clear but suggests that the CH is running on a pre-set summer time.
Any ideas on how to shut the CH down??

Neil
May 2009