72
Rinnai Tankless Water Heater
Severity: ModerateWhat Does This Error Mean?
Rinnai code 72 means flame sensing fault.
The unit lit the burner, but the flame rod did not return the expected signal — so the gas valve closed for safety.
The rod measures the small electrical current that passes through the flame.
Coating it with carbon, or weak ground continuity, is enough to drop that signal below the threshold and trigger code 72.
Affected Models
- Rinnai RU130
- Rinnai RU160
- Rinnai RU199
- Rinnai V65e
- Rinnai V75e
- Rinnai Sensei series
Common Causes
- Carbon or scale buildup on the flame rod
- Loose ground wire at the burner assembly
- Cracked porcelain insulator on the flame rod
- Gas pressure too low (especially LP installs)
- Flame rod wire damaged or pinched
- Burner ports partially clogged producing weak flame
How to Fix It
-
Power and gas off.
Switch off the breaker and shut the gas isolation valve.
Wait 5 minutes before opening the cabinet.
Combustion components retain heat — let things cool. -
Clean the flame rod.
Remove the front cover.
Locate the flame rod — a thin metal probe in the burner area, ceramic insulator at the base.
Wipe with fine emery cloth or 320-grit sandpaper until shiny.
Do not bend the rod. -
Inspect the porcelain insulator.
Hairline cracks in the white ceramic at the base of the rod let signal leak to ground.
If you see cracks, replace the rod assembly.
Genuine Rinnai flame rods are 30-70 USD. -
Confirm the ground.
The flame-sensing circuit needs a solid ground.
Check the green ground wire at the burner manifold and at the chassis bonding point.
Loose or corroded grounds cause intermittent code 72 even with a clean rod. -
Verify gas pressure under load.
A tech with a manometer can measure gas pressure at the unit while the burner is firing.
Below the spec on the data plate means the gas line is undersized or a regulator is failing.
Common on LP installs with several appliances on one tank. -
Check burner ports.
While the cover is off, look at the burner ports.
Lint or spider webs partially clogging ports produce weak flame.
Vacuum gently — no metal probes inside the ports.
Frequently Asked Questions
How often should the flame rod be cleaned?
Most installations go years without needing it.
Hard-water areas and units in dusty environments may need cleaning every 12-18 months.
If code 72 has appeared once, plan to clean the rod as part of yearly service.