Plumber, plumbing, Water Heater Repair : Gas Valve Replacement. Upon arrival the customer stated that their water heater wasn’t working properly. Upon diagnosis I found that the gas valve wasn’t working properly. When trying to swap out gas valve, I couldn’t put the new gas valve in cause there was calcium around the opening making it too hard to work had to drain tank 1st. Once I got gas valve in, got water back in tank, lit pilot, waited 25secs, set gas valve to the B setting. Checked the burner for proper flame. Ok now.