worcerster 24i junior

[ben5192]

Hi guys ive got an issue with the above boiler on start up it puffs 2 or times before it runs
almost like co's are wrong but they are spot on, had burner out electrodes etc all look fine but I cleaned them anyway,the flaps in the back of the fan are all fine gas pressure is 20mb standing and 19 on full rate any other ideas cheers in advance

once running the boiler is fine just on startup it puffs 2 or 3 times

 

[Chalked]

Try changing ionisation sensor. Somtimes, cleaning just isn't enough.

 

[ben5192]

That was my next port of call but wanted to know if I'm missing something simple before I went spending custrds cash
recommend just electrodes or leads too?

 

[mfgs]

Whats the fan pressure across the heat exchanger like?