On the covered Rinnai tankless water heater, 72 means a flame rod fault. First, reset the water heater's power once. Then: Rinnai's checks: the flame rod and its wire for damage, and that the heat exchanger is not leaking. A technician cleans or replaces the rod.
Differential
Likely causes of “Rinnai tankless water heater code 72”, and how to tell them apart
- 1
A dirty or worn flame rod
What separates it The heater lights then shuts off
How to confirm A technician cleans or replaces the rod
- 2
A damaged flame rod wire
What separates it The code returns after a reset
How to confirm Check the wire for damage
- 3
A leaking heat exchanger
What separates it Water or moisture near the burner
How to confirm Rinnai says to check that it is not leaking
- 4
Poor gas supply or venting
What separates it The flame is unstable
How to confirm Have the gas and vent checked
- 5
A control board fault
What separates it The rod tests well
How to confirm Technician diagnosis
Before you touch a setting
Record this first — changing settings destroys the evidence
- Whether the heater lights at all
- Whether water drips from the unit
- The gas type and supply
- Whether the code returns after a reset
Try in this order
0 of 8 completedWhat to do first
ReversibleReset the water heater's power once.
Correct only the documented fault domain
ReversibleRinnai's checks: the flame rod and its wire for damage, and that the heat exchanger is not leaking.
Reset the power once
ReversibleTurn the heater off and on.
Run a hot tap
ReversibleSee whether it lights.
Look for leaks
ReversibleAround the unit.
Check the vent
ReversibleFor blockage.
Do not reset repeatedly
ReversibleThe fault will not clear.
Call a technician
ReversibleFor the flame rod and wire.
Model-specific
What is true of this model and not of its siblings
- What the flame rod does
- The flame rod sits in the burner flame and carries a tiny current when a flame is present. If it cannot sense a flame, the control assumes the burner is out and shuts the gas off for safety. A rod coated with deposits, or a loose wire, gives the same reading as no flame. If you smell gas, leave the building and call your gas supplier; do not use switches or phones inside.
- Rinnai's checks
- Rinnai's own list for this code is the flame rod and its wire for damage and a check that the heat exchanger is not leaking, since water on the burner puts the flame out.
- What an owner can do
- Reset the power once and watch whether the heater lights. If the code returns, the repair is a technician's: cleaning or replacing the rod, repairing the wire or repairing the leak.
- How the sensing works
- A small current passes through the flame to the rod, and the control reads it as proof of a flame. A rod that is coated with oxide or soot, or bent out of position, passes too little current, and the control shuts the gas off after a few seconds.
- Signs before the code
- The heater lights and then goes out after a moment, or lights only on some tries. Hot water that arrives and then turns cold is a typical complaint. A heater that lights fine and then trips the code later in the cycle points at a rod that heats up and loses sensitivity.
- Water on the burner
- Rinnai also asks for a check that the heat exchanger is not leaking, since dripping water can douse the flame or short the sensing path. Water marks under the unit are a clue to report.
Stop boundary
When this stops being a self-service repair
- !Rinnai's checks are for a technician, so call one if the code returns
- !Turn off the gas if you smell it
- !Do not open a gas appliance yourself
Evidence ledger
Sources behind this answer
Exact questions
Common questions
What does 72 mean on a Rinnai tankless water heater?+
A flame rod fault.
What is a flame rod?+
A sensor that proves the burner is lit.
Can I clean it?+
A technician should.