Rinnai continuous flow hot water system code 66: Bypass flow control fault
Continuous flow hot water system, Australia
The bypass flow control device reported a fault.
This needs a licensed gasfitter. There is nothing safe to check yourself. Leave the covers on and book a professional.
What causes it
-
The bypass flow control device needs checking or replacing.
How to read this code on your unit
Booking a licensed gasfitter
Book a licensed gasfitterlicensed gasfitter
- Turn the unit off and leave the covers on. Gas components must only be serviced by a licensed technician.
- Note the code, how often it appears, and the model and serial numbers from the rating label.
- Book a licensed gasfitter and give them those details.
Models that show this code
25 models in 5 ranges
| Range | Models |
|---|---|
| Heavy Duty (commercial) | REU-AM3237WC (HD32e), REU-VCM2837FFC (HD28i), REU-VCM2837WC (HD28e), REU-NB3237WC-AK (Heavy Duty 32C), REU-NB3237FFC-AK, REU-NB3237WC-50-AK, REU-NB3237FFC-50-AK |
| Infinity | REU-AM3237W (Infinity 32), REU-AM2626WDL (Infinity 26 Touch), REU-AM2626WD (Infinity 26), REU-AM2024WD (Infinity 20), REU-AM1620WD (Infinity 16), REU-AM1220WD (Infinity 12), REU-A2626WB (B26), REU-A2024WB (B20), REU-A1620WB (B16) |
| Infinity B | REU-BM2626W (Infinity B26), REU-BM2024W (Infinity B20), REU-BM1620W (Infinity B16), REU-BM1220W (Infinity B12) |
| Infinity Enviro | REU-E2626W (Infinity Enviro 26), REU-E1620W (Infinity Enviro 16), REU-NB3237W-AK (Infinity Enviro 32), REU-NB3237W-50-AK |
| Infinity internal | REU-VCM2837FF (Infinity 28i) |
Where this comes from
- Error codes for gas continuous flow water heaters (HW Gas CF ERR) , page 5
- Infinity gas continuous flow operation and installation manual , page 12
- Infinity Enviro 32 / HDC32 operation and installation manual , page 12
Checked against the manufacturer's manual on 9 October 2026.
Other Rinnai continuous flow hot water system codes
| Code | Meaning | What you can do |
|---|---|---|
| 05 | Bypass flow control failure | Safe checks first, then a pro |
| 55 | Service reminder | Safe checks first, then a pro |
| 57 | Burner overheat switch open | Call a pro |
| 58 | Secondary heat exchanger overheat | Call a pro |
| 61 | Combustion fan failure | Call a pro |
| 63 | Recirculation low flow | Call a pro |
| 65 | Water flow control failure | Safe checks first, then a pro |
| 70 | Control board (PCB) failure | Safe checks first, then a pro |
| 71 | Gas solenoid valve failure | Call a pro |
| 72 | Flame rod circuit error | Call a pro |
| 73 | Burner thermocouple fault | Call a pro |
| 79 | Water leak detected | Safe checks first, then a pro |
See all water flow control fault codes on continuous flow hot water systems across brands.