Vitodens200 e9 error

[sdiluca]

Hi, all, I am a Viessman customer.

I had an e9 error when my vitodens 200 trys to turn on. I can hear also a explosion rumor like a boom when burner try to turn on.

My techinician changed two electrodes, cleaned up the burner, but my vitodens can't turn on.

My techinician says me that gas pressure is maybe too low (static 20mbar, dynamic 14 mbar). Could you help me to troubleshooting ?

What kind of check can I suggest to my techinician? 

I apologize for my poor english.

Thanks in advance.