I have a three year old Sime Format C boiler. For the last 4 months it has been a bit awkward in providing hot water for the shower. It might do, it might not! It only seems to affect the shower and most frequently happens if you\\\'ve flushed the toilet within about 10mins before turning on the shower. I\\\'ve topped up the pressure and bled the radiators (no air in them tho\\\'). If the central heating is on then the problem doesn\\\'t happen. When it\\\'s playing up the boiler stays on for about 30 secs, the CH light goes orange and then it turns off. It may or may not come back on again. Any ideas?