best to get it checked by gas safe engineer[UK]who can also work on LPG  equipment. First contact Truma ask if flame should rise as control knob is turned or does it ignite a second row of jets on same burner bar.
  In case you haven't Truma contact details.
Contact Details:
Email	technicalATtrumauk.com
salesATtrumauk.com
ON EMAIL ADDRESSES CHANGE THE AT  TO NORMAL EMAIL SYMBOL AS THIS FORUM DOES NOT ACCEPT EMAIL ADDRESS IN NORMAL FORM.
Website	www.trumauk.com
Telephone	01283 586050
Fax	01283 586051
 
Address	Truma UK Ltd
Park Lane
Dove Valley Park
South Derbyshire
DE65 5BG
                
 Bob
                
 May 2011