Client has a tankless water heater located in the garage that is giving error code 11. Took apart the panel to evaluate the inside of tankless heater. Perform diagnostic test of gas flow, power, inspect the venting, and clean flame rods. Tested heater and is still giving error code 11 after performing field diagnostic. Called Rheem support to run their diagnostic on the heater and found that the igniter coil has failed and would need to be replaced. Rheem is sending the part out and will arrive to our office estimated to arrive by Wednesday and schedule a to come out Thursday to put the part in and do additional work of replacing the PRV that has failed and flush the tankless heater.