Baxi Solo 2 PF 80 boiler won't fire up

Grateful for any pointers.
My Baxo Solo 2 PF 80 boiler for some time has taken a long while to fire up. Today it hasn't made it :-(
It seems it does not readily establish a solid pilot flame. 3 out of the 4 lights come on, the piezo cycles and I see it sparking. The pilot flame flicks and licks and occasionally becomes substantial enough for the main valve to open for the merest fraction of a second, long enough for the piezo to stop (perhaps just missing a single click), the burner on light blinks and the main valve shuts.
It has been taking 5-10 mins to light properly once the main burner gets a decent chance. Then the boiler seems to cycle OK as its thermostat shuts it down and then starts it up. But once cold, it has trouble again.
A new gas valve was fitted 18 months ago in an attempt to cure this behaviour, the Corgi engineer experienced with Baxi (or so he claimed) citing common problems with its diaphragm. All I could say is that the problem eased for a while, but was never "cured", to the extent that the boiler would reliable start with the first few piezo clicks.
What do you reckon is the troublesome part?
TIA
Dave
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You must have a different model Solo from the one I've come across where you couldn't see the spark or pilot through the viewing window.
If it's requiring many attempts to ingnite the pilot that suggests a problem with the pilot. The one I saw had a blocked pilot injector (tiny metal cup with 2 pinholes in it, between the pilot pipe and the nozzle.)
If it is actually lighting the pilot but the ignition is still trying that suggests a problem with the flame detection. I don't know what the flame detection mechanism is in these boilers - the one I've seen didn't have a thermocouple and the speed of response (when it did work) suggested flame rectification or optical, but there didn't seem to be a separate flame rectification electrode so I wondered if it used the spark ignition electrode? It would be a bit hairy electronics for a domestic boiler though.

(BTW the ignition isn't piezo - that's the sort where you press a button and it clicks to generate the spark. This is electronic ignition, as on cars.)
hth
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Start at the simple end and check your pilot injector (jet) is clean and clear
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I've had problems on and off with mine for a long time - ever since I was foolish enough to have it serviced.
The symptoms are that - with the outer cover on - it starts up from cold beautifully. You put the outer cover back on while it is still warm, and it runs fine. It cools down over night - and fails to start the next morning.
After getting the service people back umpteen times, and trying all manner of things, I eventually came to an understanding with it. If I promised not to over-tighten the screws holding the outer case on, it promised to work!
The screws I am talking about are the two large screws which become visible when you pull off the the lower cover to access the controls. It's quite uncanny - the thing is sitting there sparking away but not lighting, you slacken the left-hand screw by a quarter of a turn, and away it goes!
The onl;y explanation I can think of is that the spark gap is very critical (and I can't find a way of checking and adjusting it!) and that tightening this screw distorts the casing slightly and interferes with the gap.
Your problem may be due to something entirely different, but the effect of slackening the screw(s) is very quick to check - and might just help.
Roger
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