Hi i have a sime 100 format c combi boiler, When heating is switched on from cold the boiler runs for approx 10 mins then cuts off and then procceds to light up for 10 seconds then off for 20 seconds and this cycle repeats from there even though downstairs is cold. Engineer says it needs a powerflush at a cost of £600. I tend to think there is a problem within the boiler. Any ideas?
