ideal isar HE30
GCN 47-348-30
CH stays ON
2 possible causes
does C* appear on boiler display when CM927 turned off? 
[with green LED lit & sometimes flashing red LED]
if YES 
then faulty timer receiver unit sending switch live to boiler mains connector
if NO
does "d" appear regularly [when DHW not used]
most likely divertor valve seized
                
 manwithnoname
                
 May 2012