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Model VSU Make-Up Air
®
Heater Does Not Operate (Direct Spark)
Attempts to light, but no flame (Visible spark)
Troubleshooting
Check inlet gas pressure.
Reference: Start-Up - Direct Gas,
Check the Supply Gas Pressure, pg. 15
Is the low fire set properly?
Reference: Start-Up - Direct Gas,
Set the Minimum Firing Rate, pg. 17
Gas pressure between the
minimum and maximum shown
on the direct gas label?
Correct gas pressure.
Reference: Start-Up - Direct Gas,
Check the Supply Gas Pressure, pg. 15
Proper spark?
Crossed flame and spark wires.
Uncross wires and reconnect.
Incorrect spark plug gap.
Set spark plug gap to 0.062 in.
Defective spark plug.
Replace spark plug.
Pressure drop across the burner
between 0.625 and 0.675 in. WC?
Adjust burner baffles.
Reference: Start-Up - Direct Gas,
Check the Optional High and Low Gas Pressure Switches, pg. 15
Check burner pressure drop
Reference: Start-Up - Direct Gas, Check the
Optional High and Low Pressure Switches, pg. 15
Air in the gas line?
Purge gas line.
No
Yes
No
No
Yes
Yes
No
Yes
With proper airflow, gas pressure and spark,
the unit should light.
If problems remain, consult the factory.
Adjust the low fire setting.
Reference: Start-Up - Direct Gas,
Set the Minimum Firing Rate, pg. 17
No
Yes