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Model VSU Make-Up Air
®
Heater Does Not Operate (Pilot Ignition)
Visible pilot
Troubleshooting
Flame signal greater
than 1.25 VDC
Measure the flame signal
when there is a visible pilot
Pressure drop across the burner
between 0.625 and 0.675 in. WC?
Check for proper airflow
Reference: Start-Up - Direct Gas,
Set the Burner Air Pressure Differential, pg. 16
Does the flame signal
remain constant?
Adjust burner baffles
Reference: Start-Up - Direct Gas,
Set the Burner Air Pressure Differential, pg. 16
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.
Adjust the minimum firing rate.
Reference: Start-Up - Direct Gas,
Set the Unit’s Operating Temperature, pg. 18
Check the minimum firing rate
Reference: Start-Up - Direct Gas,
Set the Unit’s Operating Temperature, pg. 18
Is the minimum firing rate
set correctly?
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.
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.
Yes
Yes
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.
No
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.
No
Yes
Yes
No
No