vaillant eco tec pro fault code "F28"?

this is just a thought to try
I have have this fault F28 & F29 (recently )my book says gas problem but the Vaillant web site says to check your condensate pipe has not frozen up, i went out and separated the external pipe,it was frozen and then allowed the trapped water to run out to ground (a couple of gallons came out) the boiler then fired up will leave like this till weather improves then refit pipe

wirecutterman
December 2010

Check that gas is on and available and that the condense pipe is clear and unfrozen.

F28 is failure to establish flame

Carefree
December 2010