Water heater model: RTG-95DVLN (natural gas) 2014 build date So had this heater for 2 1/2 years and just the other day I got code 11. No issues up until this point. Thinks I have checked: Igniter sparks during startup. All solenoids are getting power and show correct resistances according to service manual. Removed and cleaned burner unit and manifold with compressed air. Check concentric vent for obstructions by looking into it from outside (comes out top of unit into immediate 90 out of wall unit is mounted on, 1.5' run). When blower comes on there is good suction on outer pipe and good flow coming out middle pipe. Now on to gas. I don't have a manometer but I made a quick and dirty one using clear tube and a ruler. There is a port on the gas inlet port. I zeroed out my makeshift manometer and turned the gas on and got 10" w.c. (spec is 7-11" for my unit). When I turn the unit on the pressure drops immediately to zero when the gas solenoid valve opens. I have 3/4" iron pipe from meter (directly on other side of wall unit is attached) and it runs about 3 feet and splits to the rest of the house and the other split is to regulator for the tankless heater. From there it is only 2 feet of pipe to the unit. I can turn on all 5 burners on my gas range (55,000 btus total) and it is fine. My tankless is 200,000 btus on full blast. Another note. I can smell gas when I'm in front of the exhaust vent but it seems it is more prevalent on the first startup. It doesn't smell strong until I let the unit sit and try to start it up again. Bad regulator for the water heater?