Tom called (Oly) my on my cell with no hot water home and the Navien tankless showing a code reading "773-00 Improper gas type". He also mentioned that the Propane tank was filled 5 to 7 days ago He called Navien per my recommendation. They will not assist him because he is not a technician with proper test equipment. I called Navien tech support after waiting on hold, opted for cue. After waiting for 30 minutes called Nick at Navien. Because the tank had been recently filled. He believes the unit has either seen a dip or a spike in pressure Nick and I gave Tom direction over the phone to correct issue: Step #1 hold "M" and "BACK" buttons at the same time for 3 seconds Step #2 click "installer menu" Step #3 type in passcode "1234" using the arrows and Ok button Step #4 select option #2 Parameter settings Step #5 scroll down to #16 gas connect error check Step #6 press ok the down arrow and ok again Step #7 select "Turn off" Water heater is now up and running. I recommend