Trane Furnace: 3 Flashes
Code 3 Flashes: Draft pressure error
Soft lockoutShown as: 3 flashes, pause, repeat
Draft pressure error. The pressure switch that proves the draft inducer is moving flue gas is not in the state the control expects, so the control will not open the gas valve.
Manual wording: “3 Flashes --- Draft Pressure Error - Possible problems a) Venting problem b) Pressure switch problem c) Inducer problem”
Documented for: *UH1 / *DH1 condensing furnaces (XR 95 family) and other Trane furnaces using the LED-only integrated furnace control
Likely causes, most common first
- Venting problem
- Pressure switch problem
- Inducer problem
- Excessive combustion pressure (wind in excess of 40 m.p.h.), vent or flue blockage
- Condensate drain blockage from debris, improper draining, or freezing condensate (condensing models)
- Induced draft blower failure - if pressure is not sensed, the contacts remain open and will not allow the gas valve to open
What you can safely check yourself
- Go outside and check the PVC intake and exhaust pipes for snow, ice, leaves, or a bird/insect nest blocking them
- Check the condensate drain line and trap for a clog, and make sure any condensate pump is working and not full
- Check that the vent terminations are clear after heavy wind or snow
When to call a technician
If the vent and intake pipes are clear and the drain is not clogged, the pressure switch, its tubing, or the inducer motor needs a technician. Never jumper or bypass a pressure switch.
A Trane furnace throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Source
- Installer's Guide - Upflow/Horizontal, Downflow/Horizontal, Gas-Fired, Direct Vent Condensing Furnaces (18-CD29D1-14-EN) (Trane, *UH1B/*UH1C/*UH1D upflow and *DH1B/*DH1C/*DH1D downflow condensing gas furnaces (XR 95 family; first letter A or T)) · checked 2026-08-25