vaillant turbo max problem

[pipestrangler]

hi there - would appreciate advice from anyone who can help
have vaillant turbomax 828 approx 5 yrs old
problem common to heating & hot water - burner seems only to ignite when it feels like it , fan starts- ignition process begins- sometimes ignites, sometimes will not ??
have replaced diverter valve complete- have also removed pcb & tried it another boiler - worked fine
any advice welcome thanks

 

[fitz1]

could be sticky solonoid on gas valve.

 

[pipestrangler]

thanx fitz1 for advice re- sticky solonoid gas valve & i am aware diy gas dabbling a big no no - cheers again

 

[cjb1971]

could be sticky aps.

 

[pipestrangler]

thanx cjb1971 excuse my ignorance but whats aps ?

 

[Rob]

Its the air pressure switch. Can you see a good spark inside the combustion chamber before it locks out?

Saw a turbomax the other day with a low water pressure switch wired in series with the gas valve so make sure your pressure is atleast 1bar.

Could also jsut need the pressures adjusting (Corgi job!)

 

[bengasman]

could be sticky aps.

bit unlikely if the ignition starts

 

[pipestrangler]

thanks to all for prompt replies re- poss sticky aps - is there a correct method for testing aps ? as i have removed it , gently blown into it & can feel what i assume is a diaphragm moving in / out . and the best bit....... on refitting all seems ok ! too early to hang the flags out ??