Payne PG8MAA Error Code Abnormal Flame-Proving Signal: Abnormal Flame-Proving Signal
What Does Code Abnormal Flame-Proving Signal Mean?
A code 22 on the Carrier HK42FZ control board indicates a setup error — the board has detected that its DIP switch configuration is invalid or doesn't correspond to a recognized furnace model. The HK42FZ board uses a bank of small DIP switches to tell it what type of furnace it's installed in, including the number of stages, blower speeds, and ignition timing. If these switches are set incorrectly, the board refuses to operate.
This error most commonly appears after a control board replacement, when the installer forgot to set the DIP switches to match the original board's configuration. It can also occur if a switch was accidentally bumped during a filter change or other service work near the control board. In some cases, the original installation manual sticker inside the furnace cabinet shows the correct DIP switch positions for your specific model.
While this code is active, the furnace will not attempt to run a heating cycle. The blower may or may not run depending on the board's failsafe behavior, but no ignition sequence will be initiated until the DIP switches are set to a valid configuration.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Stuck open or leaky gas valve | Most common | ✗ Call a pro → |
| Defective flame sensor or control board | Common | ✗ Call a pro → |
How to Fix It: Check and Correct DIP Switch Settings
What You'll Need
- Flashlight
- Small flat-head screwdriver or toothpick (to flip DIP switches)
- Furnace installation manual or wiring diagram (usually on a sticker inside the furnace cabinet door)
- Phone or camera (to photograph current switch positions before making changes)
Steps
- Turn off power AND shut off gas supply Switch the furnace power off at the disconnect switch near the unit AND at the circuit breaker. Locate the gas shutoff valve on the gas line leading to the furnace and turn it to the OFF position (perpendicular to the pipe). If you smell gas at any point, leave the area immediately and call your gas company from outside.
- Remove the furnace access panel Remove the lower front access panel of the furnace to expose the HK42FZ control board. The panel typically lifts up and pulls out, or may be held by a couple of screws. Set it aside in a safe place.
- Locate the DIP switches on the control board Find the HK42FZ control board — it's the main circuit board, usually green, with the LED status light. The DIP switches are a small bank of tiny toggle switches, typically labeled SW1 or similar. There are usually 4 to 8 individual switches in the bank.
- Photograph the current DIP switch positions Before changing anything, take a clear photo of the current DIP switch positions so you can revert if needed. Note which switches are ON (up) and which are OFF (down). The board usually has labels indicating which direction is ON.
- Find the correct DIP switch settings for your furnace model Look for the installation instructions sticker on the inside of the furnace cabinet door or on the side panel. It will show a diagram of the correct DIP switch positions for your specific furnace model number. If the sticker is missing, look up your furnace model number (found on the rating plate on the furnace) in the Carrier installation manual — these are available as PDFs on the Carrier website or HVAC forums.
- Adjust the DIP switches to the correct positions Using a small flat-head screwdriver or toothpick, carefully flip each DIP switch to match the correct configuration for your furnace model. Be gentle — these switches are small and delicate. Do not force them. Make sure each switch is fully in the ON or OFF position, not stuck halfway.
- Restore power and test Replace the furnace access panel. Turn the gas supply back on (valve handle parallel to the pipe). Restore power at the disconnect switch and breaker. Set your thermostat to call for heat. The control board will re-read the DIP switch settings on startup.
When to Call a Professional
Contact a licensed HVAC technician if:
- You cannot find the correct DIP switch settings for your furnace model (no sticker, no manual available)
- The code 22 persists after verifying the DIP switches are set correctly
- The DIP switches appear damaged, stuck, or broken
- The control board shows signs of physical damage such as burn marks, corrosion, or bulging capacitors
- You are uncomfortable working near the furnace control board