Rinnai heater RHFE-1005FTA

I have this heater it came as propane model. I ordered the conversion burner to natural gas. I changed the burner and the flame sensors . I switched the settings on the unit per the directions to my gas type , elevation and exhaust length . It will light and run with the fire box cover off . I checked the air intake for stoppages . It will not even light with cover on . I thought the gas pressure needs to be adjusted . I only have a single manometer. The high pressure adjusts fine . The low pressure won’t adjust low enough . Do I need a dual manometer ? Or should I adjust at the valve ?

The only error I get when cover is on is the 11 error .