Had the boiler installed about 3 years ago and ever since the installation it has had an intermittant problem which the installer has never been able to resolve. Most of the time the boiler works but occasionally it locks outs and the red light comes on requiring a reset which has up till now only been a minor annoyance and very infrequent. However recently despite regular servicing this is happening more frequently. The boiler scared the c**p out of me the other day when I was stood in the utility and the wife turned the hot tap on it fired up with loud bang (explosive combustion) then the very next time hot water was called for it locked out again. Gas installer called out yet again but could not find any problem. Can anyone point me in the right direction as vokera themselves have been unable to offer any solutions. 
