Furnace: No heat (ignition stage)
No heat (ignition stage) on a furnace: Generic sequence
Common causes of no heat (ignition stage)
- No 120 V/24 V
- Open door interlock
- Open limit/rollout/pressure switch
- Inducer not running
- Pressure switch not closing (blocked vent/condensate)
- Igniter not glowing (cracked/open HSI
- No output from module
- Bad transformer)
- No spark (bad lead
- Gap)
- Gas valve not opening
- Flame not proven (dirty/cracked flame rod
- Grounding
- Polarity)
- Lockout
How to fix no heat (ignition stage): step by step
- Observe how far the start-up sequence gets
- Read board flash code
- Verify 120 V at igniter then at module output
- Ohm the igniter power-off
- Confirm inducer runs and pressure switch closes
- Check limits with meter
- Manometer at manifold
- ΜA flame signal. Service scenarios: no voltage at igniter and none at module output with good igniter resistance → replace module (41A)
- Burners light then drop out, film on flame rod → clean rod (41B)
- Inducer running, pressure switch closed, igniter not glowing, igniter ohms open → replace igniter (41C)
If the unit shows an error code, look it up: AirQuest Furnace codes Carrier Furnace codes Daikin Furnace codes Goodman Furnace codes ICP Furnace codes KeepRite Furnace codes Lennox Furnace codes Midea Furnace codes Rheem Furnace codes Trane Furnace codes York Furnace codes
Source: General HVAC service practice — verify per model. Written in our own words as a summary; always check the original manual.
General guidance for qualified technicians. The manufacturer's installation and service manual and local codes always take priority. Aurora Star Tech is not affiliated with, endorsed by or sponsored by any equipment manufacturer; brand and model names are used only to identify equipment and belong to their owners.