We have a vokera 25he around 4 years old with a fault which is driving me nuts!! the boiler keep locking out showing a solid red light.if you reset,it fires up ok then runs for a few minutes and does the same.also locks out after drawing off hot water to solid red light.first boiler cycle seems ok,fires up then shuts down when return up to temp,lights all green,when it tries to re-ignite it will fire up,ignite then shut down after about 5 seconds with solid red light.removed and looped through room stat but behaves the same.gas pressure ok.so far changed thermiser,spark electrode and ignition pcb,but no different.any suggestions as to the problem as i have now spent a few quid and are debating weather to just cut my loses and replace with new boiler.would really appreciate any advise,many thanks