Carrier Furnace Code 22: Abnormal Flame-Proving Signal (Meaning, Causes, Fixes)

What the code means

Carrier status codes are two digits: the first digit is the number of short flashes and the second the number of long flashes, so code 22 is 2 short flashes followed by 2 long flashes. The furnace uses a flame sensor rod in the burner flame to prove the burners are lit. Carrier's troubleshooting guide for its variable-speed furnaces (58MVP, 58MVB and 58UVB, guide 58-06T) and its 2-stage guide (58-3T) both define status code 22 as ABNORMAL FLAME-PROVING SIGNAL: flame is proved while the gas valve is de-energized. In other words, the control isn't asking for gas, but it still sees what looks like a flame. The inducer motor runs until the fault is cleared, to keep clearing the heat exchanger. Both guides list a leaky gas valve or a stuck-open gas valve as the things to check. Their step-by-step checkout starts by shutting off the gas at the manual valve outside the furnace: if code 22 stops, the gas valve is replaced. If it keeps flashing with the gas off, the 2-stage guide calls for replacing the furnace control, while the variable-speed guide first has the sensor wire disconnected and, if that clears the code, the flame sensor cleaned and carbon deposits near the sensor opening removed before blaming the control.

Likely causes

• A gas valve that leaks through or sticks open, so a flame keeps burning after the valve has been turned off (the first thing Carrier's guides list)
• On variable-speed furnaces, a dirty flame sensor or carbon deposits in the burner box near the sensor opening giving a false flame signal
• A failed furnace control board that reports a flame signal when there is none

Safe DIY checks

1. Confirm the code: look through the sight glass on the blower door and count 2 short flashes followed by 2 long flashes. Write it down before turning power off, because a power reset clears the current flash.
2. If you can see flame at the burners while the thermostat isn't calling for heat, or you smell gas, shut off the gas at the manual valve on the gas line next to the furnace. If you smell gas, leave the house and call your gas utility or 911 from outside.
3. Shutting the gas off is also Carrier's first test: if code 22 stops flashing after the manual gas valve is closed, the gas valve is the problem and needs replacing by a qualified technician. Leave the gas off until it's repaired.
4. Don't keep resetting the furnace or turning the gas back on to see if the code returns. A gas valve that won't close is a safety hazard.
5. Don't try to adjust, repair or replace a gas valve yourself; that's work for a licensed technician.

Parts that commonly fix it

Always match the part number to your exact model.

Related codes

• 12 Carrier Gas Furnace 12
• 13 Carrier Gas Furnace 13
• 14 Carrier Gas Furnace 14
• 24 Carrier Gas Furnace 24
• 31 Carrier Gas Furnace 31

All Carrier codes →

Sources

1. Carrier 58MVP/58MVB/58UVB Troubleshooting Guide 58-06T: Status Code 22 'Abnormal Flame-Proving Signal' (flame proved while gas valve de-energized, inducer runs until cleared, leaky or stuck-open gas valve) and the step-by-step checkout (gas off, gas valve, flame sensor wire, clean sensor and carbon, replace control)
2. Carrier 2-Stage Furnace Troubleshooting Guide 58-3T: Status Code 22 'Abnormal Flame-Proving Signal' (leaky or stuck-open gas valve; gas off, replace gas valve or 2-stage control)