Carrier: Weak Flame Signal
What this fault means
The flame-proving current is too low, so the Carrier board closes the gas valve. The most common single furnace fault we see in Greater Vancouver.
Likely causes
- Oxidized flame sensor
- Poor burner ground
- Marginal combustion
- Aging sensor rod
What you can safely check
- Replace a dirty air filter — restricted airflow causes a surprising share of furnace faults.
- Confirm registers and the outdoor unit are clear of snow, leaves and debris.
- Cycle power at the switch once and let the system retry.
Call a technician — don't keep resetting this
Weak Flame Signal is a high-severity fault. Repeated resets of a safety lockout can mask a serious problem such as a cracked heat exchanger (a carbon-monoxide risk) or a failing compressor. If you smell gas, leave and call FortisBC at 1-800-663-9911 or 911 first.
Related Carrier faults
Carrier furnace showing Weak Flame Signal?
CANRO Heating & Cooling — same-day diagnosis across Greater Vancouver. Call 604-359-1081.