Quick answer
1 flash on a Goodman furnace means system lockout: the furnace tried to light three times, failed to establish or hold a flame, and stopped. It tries again automatically after one hour. Cycle power at the furnace switch once to clear the lockout and confirm the gas valve is open. If it locks out again, leave it and book service.
1 flash on a Goodman furnace means the control board has locked the furnace out after three failed ignition tries. Goodman's diagnostic chart calls it a system lockout with retries exceeded: the burners either never lit, or lit and lost their flame, three times in a row. The board waits one hour and then tries again without being asked. The chart on the inside of your furnace door is the final word, because flash codes differ between Goodman control boards.
Can you keep running a Goodman furnace that shows 1 flash?
You can let it retry, but you cannot count on it for heat. Each lockout means an hour with no heat before the next attempt, and a furnace that locks out again and again is telling you a part is failing. Leave it for service after a second lockout instead of resetting it all night. In a cold snap, look after the plumbing first: our guide to keeping pipes from freezing when the furnace fails covers the first few hours.
The one safe step: cycle the power once and check the gas valve
- Read the light first. Count the flashes through the small viewing window in the furnace door before you touch the switch, because interrupting power clears the lockout.
- Switch the furnace off at the wall switch beside it (it looks like a light switch), wait a minute, and switch it back on. The furnace starts a fresh ignition sequence.
- Confirm the gas shut-off on the pipe beside the furnace is open: the handle sits in line with the pipe when open and crosswise when closed.
- Check your other gas appliances. If the range and the water heater have no gas either, the problem is the supply, and that call goes to Enbridge Gas.
- Reset once only. A second lockout is a repair call.
What causes a 1 flash lockout, most likely first
The causes split two ways: the flame never established, or it lit and then dropped out. Watching one ignition attempt through the door window tells you which, and it is the most useful thing you can report on the phone.
- A coated or oxidized flame sensor. The burners light, run for a few seconds and shut off, three times over. Goodman's chart has an early-warning code for a weakening flame signal, 7 flashes, and a furnace that showed it last season is a strong candidate.
- A bad or misaligned igniter. No orange glow, or a glow with no ignition, means the hot surface igniter is cracked, weak or sitting out of position.
- No gas to the burners. A closed shut-off, an interrupted supply or a gas valve that does not open leaves the igniter glowing at nothing.
- A pressure switch opening during the cycle. When the draft signal drops out, the board closes the gas valve and counts a failed try.
- Lazy flame from wrong gas pressure or a restricted flue. A flame that lifts or wanders off the sensor reads to the board as no flame at all.
A normal Goodman start runs in a fixed order: the inducer starts, the igniter glows, the gas valve opens and the burners light, and the main blower follows a little later. Note the step where yours stops. A furnace that glows and never lights sends the technician to different parts than one that lights and quits after a few seconds.
What a technician checks on a Goodman lockout, and what it costs
Igniter, flame sensor and gas pressure checks are work for a TSSA-licensed G2 gas technician. The visit covers the flame signal in microamps, the condition and position of the igniter, the gas pressure at the valve with a manometer, and the draft through the vent. The repair is usually one part, and the common ones have published prices.
- The visit to find the fault: $90–$150, credited when the repair is approved.
- Flame sensor cleaning or replacement: $150–$300.
- Hot surface igniter: $200–$450.
- Pressure switch: $250–$500.
- Gas valve: $500–$1,000.
If your Goodman locks out a second time, call (647) 801-1252 or book a furnace repair visit. ZK Mechanical handles furnace repair across Burlington, Oakville, Milton and Hamilton, with written pricing before the work starts. For every other flash count, see the Goodman furnace error code guide, and for how the timers behave on other brands, read how long a furnace lockout lasts.