i have a 6 years old suprima 30 boiler from potterton. the last month it has been 'not right'. whilst on the timer, it would come on at the preset times but the duration of which is variable - from a few minutes to long enough to, i presumed, reach the pre-set water temperature before the boiler locks-out (red-light flashing). i would then have to manually press on the reset button to get the boiler working again. once it started the work again, the same scenario holds true i.e. it would then be on for a variable duration before locking out again. the same would happen when i set the boiler to be 'on' at all times i.e. it would work for a variable duration before it locks out requiring resetting.
can anyone advice/help as to: 1. what is the likely fault, 2. how to rectify it, and 3. whether it can be done safely as diy.
thank you all,