My Alpha 280E boiler has the following problem -9 times out of 10 it is OK. Sometimes, you switch on the combi as normal [hot water say] -pump comes on, all sounds good but no ignition! A plumber told me it could be the DHW flow valve diaphragm -on inspection both plunger valves [inc. primary flow] work OK [he also though it could be the whole assembly [both valves were working fine when he looked at it so was difficult to diagnose]. What else could it be -a sensor?

PW, June 2009

Thanks for your answer....most times -sparks & lights as normal -the other times, no spark or lighting -after pump coming on. If blocked pipes surely would not light at all?

PW, June 2009

when you say that it try to light 9 time, do you see or hear it spark clicking ?? if there is no sparking ie clicking then its your air presser swich or its block pipes, if you do say YES i hear it sparking ie clicking then its your gas valve not opening ,let me know how you get on

capitalboilers.co.uk, June 2009