York Gas Furnace: PHU
Re: Burners Ignite & Shut Off
Code 7 = Failure to Sense Flame
Qty |
Possible Causes: |
2 |
Dirty Flame Sensor |
|
Clogged Burners |
|
No or Low Gas Pressure |
|
Pressure Switch Trip |
|
Bad Control Board |
|
Thermostat Cycling |
CHECKOUT:
1. Check Diagnostic Indicator
- DO NOT cycle power to the furnace.
- The furnace control board has an on-board LED that will flash to show any active diagnostics. (Killing power clears the diagnostic.)
- Look through the blower door sight glass to see if the LED is flashing.
2. Check Ignition
- Initiate a call for heat from the thermostat.
- 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.
3. Check Controls
- Monitor 24VAC from "W" to "C" while the furnace cycles. (It may be necessary to manually close the door switch.)
- Power Drops-Out when Burners Cycle = Thermostat Short-Cycling ⇒ Check Thermostat & Wiring
- Power Consistent ⇒ Continue
- Monitor the diagnostic indicator when the burners shut-off.
4. Check Gas Pressure
- Inlet Gas Pressure
- Check the inlet gas pressure.
- Minimum Pressure = 5" w.c. for Nat. gas, and 11" w.c. for propane.
- 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 = Bad Meter/Regulator or Restricted Gas Line
- Manifold Gas Pressure
- Check the manifold gas pressure.
- Normal Pressure = 3 - 3.5" w.c. for Nat. Gas, 9 - 11" w.c. for LP
- Low Gas Pressure ⇒ Increase Manifold Gas Pressure
- Normal Gas Pressure but No or Delayed Ignition = Clogged Burners ⇒ Remove burners and clean spreaders.
5. Check Flame Sensor
- DO NOT clean the flame sensor before testing.
- On the multi-meter:
- Switch the test leads to "COM" and "mA".
- Set the meter on DC 200ù.
- Check the flame reading when the burners ignite.
- Normal Reading = 2 to 6 mA
- Minimum acceptable reading = 1 MicroAmp
- Low Reading = Dirty Flame Sensor ⇒ Clean Flame Sensor & Re-check
- CAUTION! Move meter leads back to "COM" and "V" before proceeding!