Greenheck Fan Troubleshooting Guide for Greenheck Differential Pressure Units in Gas Heaters
Page 28

Troubleshooting

Heater Does Not Operate (Pilot Ignition)

Visible pilot

Measure the flame signal when there is a visible pilot

 

 

 

 

 

Flame signal greater

No

 

 

than 1.25 VDC

 

 

 

 

 

 

 

 

 

 

 

 

Yes

 

 

 

 

 

 

 

 

 

 

 

 

Check for proper airflow

 

 

 

Reference: Start-Up - Direct Gas, 

 

 

 

Set the Burner Air Pressure Differential, pg. 16

 

 

 

 

 

 

 

 

 

 

 

 

 

Pressure drop across the burner

No

 

 

between 0.625 and 0.675 in. WC?

 

 

 

 

 

 

 

 

 

Yes

 

 

 

 

 

 

 

 

 

 

 

 

 

Check the minimum firing rate

 

 

 

Reference: Start-Up - Direct Gas,

 

 

 

Set the Unit’s Operating Temperature, pg. 18

 

 

 

 

 

 

 

 

 

 

 

 

 

Is the minimum firing rate

No

 

 

set correctly?

 

 

 

 

 

 

 

 

 

Yes

 

 

 

 

 

 

 

 

Does the flame signal

No

 

 

remain constant?

 

 

 

 

 

 

 

 

 

Yes

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Note: The flame signal should be steady and above 1.25 VDC with a visible pilot.

Reference: Start-Up - Direct Gas,

Flame Signal Check - Pilot Ignition, pg. 18

Unit is not grounded.

Properly ground unit.

Flame rod is grounding out.

Adjust the flame rod to avoid contact with the burner or the unit.

Cracked porcelain on flame rod.

Replace flame rod.

Note: When the pressure is low or marginal and the unit

begins heating, the air density will change. This can cause the pressure to drop below the minimum setting. Also, low airflow can cause the flame to walk out of the burner and away from the flame sensor, causing the unit to recycle.

Adjust burner baffles

Reference: Start-Up - Direct Gas, 

Set the Burner Air Pressure Differential, pg. 16

Note: Burners greater than 36 inches in length use an interrupted pilot. The pilot is turned off 10 seconds after lighting the main burner and the flame safeguard monitors the main flame instead of the pilot flame. If the minimum fire is set too low, the flame safeguard may not be able to sense it.

Adjust the minimum firing rate.

Reference: Start-Up - Direct Gas,

Set the Unit’s Operating Temperature, pg. 18

If the signal slowly drops off, typically the airflow is too low.

Reference: Start-Up - Blowers, Set the Maximum Firing Rate

If it suddenly drops to zero, the flame rod is grounding out. Adjust the flame rod to avoid contact with the burner or the unit.

If the flame signal is above 1.25 VDC and constant, the main gas valves will remain open until the call for heat is interrupted or the unit is shut down.

28Model VSU Make-Up Air

®

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Page 27 Page 29
Contents Installation, Operation and Maintenance Manual Model VSU General Safety InformationInspection and Maintenance during Storage ReceivingUnpacking HandlingTable of Contents Product Overview SubassembliesBurner, Blower and Control Center Section Open ViewControl Center Burner SubassemblyDampers Installation Installation of Optional Service Platform Complete InstallationService Platform Material List Assembly Figure CInstallation of Electrical Wiring Install Additional Regulator if Required Installation of Direct Gas PipingDetermine the Supply Gas Requirements Installation of Building Pressure Control optional Unit Model Number Start-Up ChecklistCheck blower rotation Check for vibration Supply fan RPM Start-Up Blower Check the Optional High and Low Gas Pressure Switches Start-Up Direct GasSet-Up Optional Components Check the Supply Gas PressureMaximum firing rate adjustment Set the Burner Air Pressure DifferentialSet the Maximum Firing Rate Measuring the Pressure DropRegulators and Modulating Valves Set the Minimum Firing RateFlame Signal Check Pilot Ignition Set the Unit’s Operating TemperatureMaxitrol Series 44 9 Terminals The Maxitrol Variable Volume Operation Operation VAV Units optionalSpeed ModulatingOperation Recirculating Units optional Operation ElectricalRecirculation Operation Electrical Sequence Exhaust Fan Contact S1 Closed optionalFlame Safeguard FSG Sequence 3a. Heat Contact S4 Closed Pilot Ignition3b. Heat Contact S4 Closed Direct Spark Heat Contact ClosedTroubleshooting Blower Does Not OperateMotor Overamps Insufficient Airflow Too Much Airflow Excessive Noise or Vibration Heater Does Not Operate Pilot Ignition Does not attempt to light No visible sparkAttempts to light, but no pilot visible spark Visible pilot Between 0.625 and 0.675 in. WC?Heater Does Not Operate Direct Spark Attempts to light, but no flame Visible spark Maintenance Routine Belt DrivesMotors WheelsMaintenance Fall Reference Typical Gas Train Layout with Direct Spark Ignition Dirty Filter Switch Fan Relay allows power to pass to energize motor starterHeat Relay allows power to pass to heating controls Control Center LayoutWarranty Maintenance LogDateTime AM/PM
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