Carrier Gas Furnace: 58ZAV
Re: Flashing Code 34
Code 34 = Failure to Sense Flame
Flash Sequence = 3 Short Flashes + 4 Long Flashes (- - - , — — — —)
Qty |
Possible Causes: |
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Dirty Flame Sensor |
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Bad Glow Plug |
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Clogged Burners |
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No or Low Gas Pressure |
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Bad Gas Valve |
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Bad Control Board |
CHECKOUT:
1. Check Ignition Sequence
- Initiate a call for heat from the thermostat and monitor the ignition sequence.
- If there is 24V on "W" at power-up, the furnace will run the blower for 90 seconds and flash a Code 12.
- 1. The inducer motor should start with no difficulty.
- 2. The glow plug should energize within 30 seconds of the pressure switch closing.
2. Check Glow Plug
- Use a meter to test resistance of the glow plug.
- No Resistance = Bad Glow Plug
- Re-start an ignition sequence.
- Check for 120VAC power on the 2-wire plug feeding the glow plug during an ignition sequence.
- No Power = Bad Ignition Control
- Power Present + No Glow = Bad Glow Plug
3. Check Ignition
- Visually inspect the burners during ignition.
- The burners should light smoothly with little or no delay from the glow plug to the flame sensor.
- Make sure the flame sensor comes in good contact with the flame.
4. Check Gas Pressure / Valve
- Check Inlet Gas Pressure
- Minimum Pressure = 5" w.c. for Nat. gas, and 10" w.c. for LP.
- Low Pressure = Gas Supply Issue
- Re-apply power to the furnace and activate a call for heat.
- Make sure the inlet gas pressure stays above minimum when the gas valve energizes.
- Pressure Drops Below Minimum = Gas Supply Issue
- Check Manifold Gas Pressure
- Normal Pressure = 3 to 3.5" w.c. for Nat. Gas, 9 to 11" w.c. for LP.
- Activate a call for heat and monitor the manifold gas pressure during an ignition attempt.
- No Gas Pressure = Bad Gas Valve
- Low Gas Pressure ⇒ Attempt to Increase Manifold Gas Pressure
- Won't Increase = Bad Gas Valve
- Normal Gas Pressure + No or Delayed Ignition = Clogged Burners ⇒ Remove burners and clean spreaders
5. Check Flame Sensor
- Check the flame sensor reading when the burners ignite.
- Normal Reading = 2 to 6 mA
- Minimum acceptable reading = 1 MicroAmp
- Normal Reading + Burners Shut-Off after 4-6 seconds = Bad Control Board
- Low Reading = Dirty Flame Sensor ⇒ Clean the Flame Sensor & Re-check
- CAUTION! Move meter leads back to "COM" and "V" before proceeding!