In message , John Stumbles
writes
Had a Worcester 19/24 CBi which wouldn't fire up today. The fan would run
but no ignition. I pulled off the tubes from the pressure switch and
blew and sucked into them and the pressure switch clicked. After
that (after reconnecting the tubes) the boiler fired up OK.

The fan ran smoothly and quietly so I'm guessing the pressure switch is
getting a bit dodgy, but before replacing that I thought I'd ask
around in case there's some subtle problem with the fan on these
machines. Geoff? (And if it is the switch do you do those too?)

Fan - no strange behaviour that I know of

really sounds like an APS problem, It could be some crud lodged
somewhere that you dislodged or a high spot on a microswitch contact,
muck in a pipe or something

difficult to say and a problem to get top the bottom of if the problem
has (temporarily) resolved itself

No, we don't do APS's - not really repairable items

--
geoff