An error code 91 means incorrect gas type.
For new installs:
1. Check for gas type, gas orifice and gas type setting.
2. Check for proper unit settings. (Vent type, length, size or elevation)
3. Check the unit is installed according to the guidelines found in the installation manual either included with the unit or downloaded from our support site here: http://support.noritz.com/technical-literature
For existing installations:
1. Check for gas type, gas orifice and gas type setting.
2. Check for proper unit settings. (Vent type, length, size or elevation)
3. Check the unit is installed according to the guidelines found in the installation manual either included with the unit or downloaded from our support site here: http://support.noritz.com/technical-literature
This error code can be reset by unplugging the heater for 30 seconds and then plugging it back in.
For further technical assistance call 866-766-7489 or use our Contractor Locator to find a local service representative.