Arrived on site and customer stated that he was getting a code 11 on his tankless water heater. He mentioned that he unplugged the unit and plug it back in a couple of times before the error code went away. When I arrive today, he said as of today, the unit did not throw an error code. I went ahead and explain to him that I would run a diagnostics on the unit to determine why the unit was throwing a code 11. After troubleshooting with Rinnai, we found that the unit was receiving almost 17 inches of water column. And when fired, dropped down to about 8 to 9 inches of water column. He stated that the gas coming in was way too high, which was causing the unit to misfire. I informed the customer that he would need to reach out to the gas company and have them check their regulator at the meter as the gas coming and is causing too much pressure.