On the covered Noritz tankless water heater, 73, EC73 means a circuit board setting problem, triggered by a jumper or dip switch changed while power was supplied, or an improperly programmed board. It applies to all models. First, unplug the heater for 30 seconds and plug it back in once.
Differential
Likely causes of “Noritz tankless water heater code 73, EC73”, and how to tell them apart
- 1
A dip switch or jumper changed with power on
What separates it The board rejects the setting
How to confirm Disconnect power and set it correctly
- 2
An improperly programmed board
What separates it A replacement board without settings
How to confirm Transfer or program the settings
- 3
A wrong setting after service
What separates it The code appears right after a visit
How to confirm Technician corrects it
- 4
A damaged board
What separates it
How to confirm Replace the board
- 5
A power glitch
What separates it A one-off code
How to confirm Unplug for thirty seconds
Before you touch a setting
Record this first — changing settings destroys the evidence
- Whether a technician worked on it recently
- Whether a board was replaced
Try in this order
0 of 6 completedWhat to do first
ReversibleUnplug the heater for 30 seconds and plug it back in once.
Correct only the documented fault domain
ReversibleNoritz says any change to dip switches or jumper wires must be done with the unit disconnected from power, and to follow the instructions supplied with a replacement circuit board to transfer or program the settings.
Plug it back in
ReversibleOnce.
Do not touch dip switches
ReversibleWith power on.
Check any recent service
ReversibleFor setting changes.
Follow the board instructions
ReversibleIf replaced.
Model-specific
What is true of this model and not of its siblings
- Settings live on switches
- The board reads dip switches and jumpers to learn the model, gas type and options. If one changes while the unit is powered, or a replacement board is not set up to match, the board flags a setting problem.
- Noritz's advice
- Any change to dip switches or jumper wires must be done with the unit disconnected from power, and the instructions supplied with a replacement board explain how to transfer or program the settings.
- Technician work
- A technician should set these.
- Never change switches under power
- A dip switch or jumper moved while the board is powered can corrupt its stored settings. Always disconnect power first, wait, change the switch and then restore power. Noritz repeats this because the board reads its settings at power-up.
Stop boundary
When this stops being a self-service repair
- !Noritz says changes to dip switches or jumpers must be made with power disconnected
- !Follow the instructions with a replacement board
Evidence ledger
Sources behind this answer
Exact questions
Common questions
What does 73, EC73 mean on a Noritz tankless water heater?+
A circuit board setting problem, triggered by a jumper or dip switch changed while power was supplied, or an improperly programmed board. It applies to all models.
What does code 73 mean on a Noritz?+
A circuit board setting problem.
What causes it?+
A jumper or dip switch changed while powered, or a wrongly programmed board.
Does it apply to all models?+
Yes.
How do I clear it?+
Unplug for thirty seconds, once.