Vaillant 282 non-hot starting

[onthecut]

Hoping someone can point me in the right direction --- Vaillant 282 Turbomax.

System cold, boiler fires up fine and works fine in every respect. Once warmed through (say 20 - 30 minute use), whether looking for water or heating, it will fire, with a minimal flame, doesn't increase the flame size then trips out, leaving the flame fail lamp on. Bypassing the lockout while it's hot produces the same sequence.
The fault charts dont precisely cover this. For reference, both circuit boards are new (same symptom with new or old boards) and a complete new gas valve assembly (operator, solenoid etc.) Am now pondering NTC sensor or air switch --- any thoughts most welcome.

Mike.

 

[Boilerman2]

Forget the air switch -it wouldn't fire at all ,
I have come across a similar problem on this model but it was due to the gas control valve so thats not much help to you...
However get a RGI to check the inlet gas pressure at the boiler and meter outlet it could be a problem with the meter governor??? possibly
a RGI would be able to check this out for you

 

[adlplumbing]

to be honest i think you need to call some one out as it could be any number of things and it could be has related

 

[The831Bunny]

Check the pressure differential switch and tubes are not blocked.

Also a Gas Safe engineer needs to check the minimum burner rate setting pressure is correct and the HT and rectification probes, leads and connections to the PCB are OK.