We are getting error code 501 when switching on our Ariston Clas he boiler - can anyone tell us what this code means and if possible how it can be resolved?

jason, October 2009

Error 501 is "no flame detectect" after 2 ignition attempts. My boiler does this as well and pressing the reset is usually enough to get things working again.
It is annoying as it seems to be getting worse (occurs more often) so the heating can't be trusted to startup when required.

Bob, November 2009