Trane and American Standard Furnace 3 flashes: Pressure switch fault
Updated October 2026 · Sourced from Trane and American Standard documentation
🛑 Turn it off and call a licensed pro
Trane and American Standard 3 flashes means different things on different series:
- Trane and American Standard single-stage furnaces serviced with the SiNi igniter control kit (*UH1, *DH1, *UD1, *DD1 families and M951): The control reports a pressure switch fault.
- Trane and American Standard modulating communicating *UHM/*DHM furnaces (e.g. *UHMB060ACV3VB, *UHMC100ACV4VB, *UHMD120ACV5VB and matching DHM models): The alert group is a pressure switch failure, open or shorted, on the first, second or third stage.
Is it safe to keep running? No. Turn it off and get it checked. Call a licensed HVAC technician. Pressure switch, tubing, inducer and vent checks need professional tools.
3 flashes at a glance
| Code / how it shows | Meaning | Applies to |
|---|---|---|
| 3 flashes Red LED on the integrated furnace control blinks 3 times, then pauses | Pressure switch fault | Trane and American Standard single-stage furnaces serviced with the SiNi igniter control kit (*UH1, *DH1, *UD1, *DD1 families and M951) |
| 3 flashes Red fault LED on the integrated furnace control blinks 3 times | Pressure switch failure | Trane and American Standard modulating communicating *UHM/*DHM furnaces (e.g. *UHMB060ACV3VB, *UHMC100ACV4VB, *UHMD120ACV5VB and matching DHM models) |
Check this first
Only steps a homeowner can do safely. Do not open electrical panels or the burner area.
- Look outside at the furnace vent and intake pipes for snow, leaves, nests or other blockage, and clear anything you can reach safely.
- Check that the condensate drain line is not visibly blocked, kinked or overflowing.
- Replace a dirty air filter, then restore power and see if the code returns.
- Turn the furnace power switch or breaker off for 30 seconds, then back on, and see if the code clears.
🛑 Stop and call a licensed pro if
- Call a licensed HVAC technician. Pressure switch, tubing, inducer and vent checks need professional tools.
- Call a licensed HVAC technician. Pressure switch and inducer tests need professional tools.
- You smell gas. Leave the house, do not touch switches, and call your gas utility from outside.
- Flame rollout, limit or pressure switch codes that come back after one reset.
- Anything involving the control board, gas valve, flame sensor, igniter or venting.
- A carbon monoxide alarm sounds. Get everyone outside and call 911 or the fire department.
Safe first steps for any Trane and American Standard code
- Count the LED flashes through the blower door window before you switch anything off. Cutting power can clear the code.
- Replace or clean the furnace air filter.
- Check the thermostat: correct mode, set above room temperature, and fresh batteries.
- Make sure the furnace power switch and breaker are on. If the furnace has locked out, turning the power off and back on once restarts it.
- Make sure the gas valve is in the ON position, following the lighting instructions on the furnace label only.
- On high-efficiency furnaces, look at the outside vent and intake pipes for snow, ice, leaves or nests (look only, do not take pipes apart).
Sources: Trane Service Installer's Guide 18-CH93D1-1A-EN (Jul 2020), Integrated Furnace Control Diagnostic Codes; Trane Installer's Guide 18-CD30D1-20-EN (06/2020), Table 24 Furnace Alert Codes, p.55. Codes are series-specific, so your unit's own manual is the final word. Reviewed October 2026.
Shaun Cain · Certified HVAC & Refrigeration Technician · Ask an HVAC technician
Related Trane and American Standard codes
2 flashes : System lockout, retries or recycles exceeded4 flashes : Open limit switch5 flashes : Flame sensed when none should be present6 flashes : 115 volt power reversed or improper ground7 flashes : Gas valve circuit error8 flashes : Low flame sense signal9 flashes : Igniter relay fault10 flashes : Communication faultE2.1 : Retry exceeded (flame never sensed)E2.2 : Recycles exceeded (flame lost)E3.1 : Shorted pressure switch, 1st stageE3.2 : Open pressure switch, 1st stage