Vaillant turbomax plus - S33 code

[Moibr]

The boiler does not ignite, neither for hot water nor heating, After a few seconds of switchingit on an 'S33' code comes up (this code stands for 'check air/flue system'). I had this problem 4 months ago, and was told to replace the air pressure switch - I did this and it solved the problem. However, 4 months later the same problem is occuring again. Would the air pressure switch develop a fault that quickly? or could it be another cause.... Any help would be much appreciated.

 

[cross thread]

moisture/rain water in ap tubes?

 

[chrishutt]

If you press the i and +buttons simultaneously you will access the diagnostic codes. Scroll to d.24. This will tell you if the APS is open or closed.

 

[gasgeezer]

Have had this acouple of times, on the aqua plus as well in my case changing the fan cured the problem it was not modulating properly but these are only fitted to the larger models so may not apply to you.