HVACopediaNTI · Boiler
Alert 128 Modulation limited - air switch open
What the control is telling you
Firing rate was held down because the interrupted air switch input reads open.
Applies to: Trinity Tft60, Tft85, Tft110, Tft154, Tft201, Tft285, Tft340, Tft399
Likely causes
- Wrong control board fitted for this model
Test and repair steps
- Replace the control with the correct model
Models that show this code
13 models in Trinity Tft
Other codes on the same units
- Alert 126 Modulation rate was limited due to anti-condensation
- Alert 127 Fan Speed out of range in RUN
- Alert 127 Fan Speed out of range in RUN
- Alert 128 Modulation limited - air switch open
- Alert 129 Slow start ramp setting of zero will result in no modulation rate change
- Alert 129 Slow start ramp setting of zero will result in no modulation rate change
- Alert 13 Annunciation configuration was restored from backup
- Alert 13 Annunciation configuration was restored from backup
Save it for the next call
Star this code in the HVACopedia app and keep the whole library on your phone for jobs with no signal.
Source: NTI Trinity Tft399 Installation and Operation Manual (2018-09-07), Sec. 16.0 Troubleshooting, Table 16-4. 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.