HVACopediaRinnai · Wall furnace
33 Overheat thermistor 1 open circuit
What the control is telling you
The manual lists this as a service-call fault: the overheat thermistor 1 circuit is open (disconnected).
Applies to: Rinnai EnergySaver direct vent wall furnaces EX08DT, EX11DT, EX17DT, EX22DT
Likely causes
- Overheat thermistor 1 disconnected or circuit open
Test and repair steps
- Turn the furnace off and back on with the ON/OFF button to try to clear the code.
- If the code stays or comes back on the next operation, a trained and qualified technician must service the unit.
- Technician inspect the part named in the code (overheat thermistor 1 open circuit) and its connections, and repair or replace as needed.
Settings for these units
Clearances to combustibles and service · EX DT
| Location | Clearance |
|---|---|
| Top | 0 in. (0 mm) |
| Bottom / ground | 0 in. (0 mm) |
| Front (panel) | 40 in. (1 m) - flooring or carpet under 1.2 in. (30 mm) high not included |
| Back (including back spacer) | 0 in. (0 mm) |
| Sides (left and right) | 2 in. (50 mm) |
| Service access | 10 in. (254 mm) sides; 40 in. (1 m) front; area above per figure |
| Exhaust extension pipe | 1 in. (25.4 mm) to combustibles; 0 in. to non-combustibles |
Rinnai recommends 10 in. (254 mm) at top and both sides for servicing.
Service clearance figure above the unit: 10 in. (254 mm) on EX08DT/EX11DT, 9 in. (229 mm) on EX17DT/EX22DT.
Models that show this code
5 models in EX DT
Other codes on the same units
- 16 Room overheat (above 104°F / 40°C)
- 30 Overheat temperature thermistor 2 open circuit
- 31 Room temperature thermistor open circuit
- 32 Room temperature thermistor short circuit
- 34 Overheat thermistor 1 short circuit
- 35 Overheat temperature thermistor 2 short circuit
- 40 Pressure sensor sensing tube failure
- 49 Pressure sensor breakdown
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Source: Rinnai EX08DT/EX11DT and EX17DT/EX22DT Installation and Operation Manuals (200000083, 200000084), Table 9 'Diagnostic Codes', p.35–36. Summarized in our own words; check the original manual for your model.
Homeowner looking at this code? See what it means for you and when to call a technician.
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.