Noritz tankless water heater - burner stays on with no demand

by Mitch
(Dallas, TX)

Just recieved my $270 gas bill which normally runs $25-$30 this time of year. The water heater is the only thing using gas at this time. I checked the unit in the attic and noticed the burner light was on with no demand in the house. I checked the gas meter and it was spinning like crazy. I turned off the power to the unit and the gas meter stopped. I'm sure this is some sort of issue with a relay. Anyone know how to troubleshoot / replace?