HVACopediaGlow Brand · Boiler
Err 120 CH supply temperature sensor open
What the control is telling you
The control reads the ch supply temperature sensor as open (10 kohm NTC).
Applies to: B85, B120, B160 (NG and LP)
Likely causes
- Sensor open
- Sensor wiring or connector
Test and repair steps
- Measure the sensor it should read about 10,000 ohm at 77 F (25 C); use the resistance table for other temperatures.
- If the resistance is right, check the wiring between sensor and control.
- Replace the sensor.
Settings for these units
Maintenance intervals · Glow B85/B120/B160
| Item | When |
|---|---|
| Annual inspection by a technician | Every year (warranty) |
| Relief valve try-lever test | Annually |
| LWCO test | Annually |
| Condensate trap clean | Annually (14.3) |
| Heat exchanger combustion-side wash | Annually or when combustion drifts (14.4) |
| Burner door silicone gasket | Replace if damaged or after 2 years |
| Service reminder | 2.203 on, interval 2.204 (default 1000 days) |
Operating pressure should sit 5 psi under the relief valve rating (max 25 psig on a 30 psi valve); water never above 180 F.
Models that show this code
3 models in Glow B85/B120/B160
Other codes on the same units
- Err 113 Internal software error (blocking)
- Err 114 False flame detected
- Err 116 Low water pressure (FILL)
- Err 119 CH return temperature sensor open
- Err 122 DHW tank temperature sensor open
- Err 123 Flue temperature sensor open
- Err 126 CH return temperature sensor shorted
- Err 127 CH supply temperature sensor shorted
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Source: Glow Brand B85/B120/B160 Installation & Operation Manual V20231025, Table 12.2 p.65. 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.