Ace Pelizon Plumbing was called out on tankless water heater not working. Ace Pelizon Plumbing found noritz NR 98 sv with circulation pump connected and running 24/7. Causing 990 constant running water error to appear. Customer used to have a timer but it is currently disconnected. Customer has a thermal switch attached to circulation line that is supposed to shut off pump. *switch most likely gone bad. Ran diagnostic of water heater through control panel. 91 - 90 combustion error 92 - 90 combustion error 93 - 12 burner flame loss Ace Pelizon Plumbing found multiple burner errors prior to arrival. At minimum it is recommended for a tank flush and cleaning of burner intake, ignition plug and flame rod. *unknown if temp sensor has gone bad until water heater is back in operation. Put water heater back in operation and verified function with customer on site.