HVACopediaRinnai · Tankless water heater
72 Flame rod fault
What the control is telling you
The flame rod circuit is not sensing flame properly, due to wiring, rod position, carbon build-up, low flame current, a heat exchanger leak or a board fault.
Applies to: SENSEI Series, SENSEI RX/CX Series, Non-SENSEI Series
Likely causes
- Broken or damaged flame rod wiring
- Flame rod not contacting the flame
- Carbon build-up on the flame rod
- Flame current below 1 micro amp
- Leaking heat exchanger
- Faulty PC board
Test and repair steps
- Inspect the harness from the flame rods to the PC board for broken or damaged connections.
- Confirm the flame rod sits in the flame when the heater fires.
- Remove the flame rod and look for carbon build-up; replace the rod and gasket if needed.
- Measure flame rod output; it must hold at least 1 micro amp.
- Replace the flame rod and its gasket.
- Check the heat exchanger for leaks and replace it if necessary.
- Replace the PC board.
- SENSEI Transfer data from the old board with the supplied cable, or program all parameters manually per PCB Replacement Instructions (100000553).
- SENSEI RX/CX Transfer data from the old board with the supplied cable, or program all parameters manually per PCB Replacement Instructions (100000854).
Settings for these units
RSC supply connection sizes · SENSEI
| Connection | Size |
|---|---|
| Gas | 3/4 in. NPT |
| Cold inlet | 3/4 in. NPT |
| Hot outlet | 3/4 in. NPT |
| Condensate drain | 1/2 in. NPT |
| Pressure relief valve | M33 thread |
The PRV and its adapter come in the box; PRV must be rated 150 psi and at least the heater Btu/h.
Condensate drain line must stay at least 1/2 in. over its whole length.
RSC water quality limits · SENSEI
| Contaminant | Maximum level |
|---|---|
| Total hardness | Up to 200 mg/L |
| Aluminum | Up to 0.2 mg/L |
| Chlorides | Up to 250 mg/L |
| Copper | Up to 1.0 mg/L |
| Dissolved CO2 | Up to 15.0 mg/L |
| Iron | Up to 0.3 mg/L |
| Manganese | Up to 0.05 mg/L |
| pH | 6.5 to 8.5 |
| TDS | Up to 500 mg/L |
| Zinc | Up to 5 mg/L |
Damage from water above these limits is not covered by warranty.
Hard water should be treated; use the Service Soon (SS) reminder (parameter 03) for flushing intervals.
- RSC clearances to combustibles · SENSEI
- RSC temperature settings available · SENSEI
- RX supply connection sizes · SENSEI RX/CX
- RX water quality limits · SENSEI RX/CX
- RX water treatment and flushing by hardness · SENSEI RX/CX
- RX clearances to combustibles · SENSEI RX/CX
Models that show this code
89 models in Non-SENSEI, RH180 hybrid, SENSEI RX/CX, SENSEI
Other codes on the same units
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Source: Rinnai Troubleshooting TWH Diagnostic Codes (100000652), p.60. Summarized in our own words; check the original manual for your model.
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For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.