Maintenance - Greenheck VSU Installation, Operation And Maintenance Manual

Troubleshooting
Heater Does Not Operate (Pilot Ignition)
Visible pilot
Measure the flame signal
when there is a visible pilot
Flame signal greater
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
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
set correctly?
Yes
Does the flame signal
remain constant?
Yes
28 Model VSU Make-Up Air
Note: The flame signal should be steady and
Flame Signal Check - Pilot Ignition, pg. 18
No
Adjust the flame rod to avoid contact with the burner or the unit.
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.
No
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.
No
Set the Unit's Operating Temperature, pg. 18
No
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.
above 1.25 VDC with a visible pilot.
Reference: Start-Up - Direct Gas,
Unit is not grounded.
Properly ground unit.
Flame rod is grounding out.
Cracked porcelain on flame rod.
Replace flame rod.
Adjust burner baffles
Reference: Start-Up - Direct Gas,
Adjust the minimum firing rate.
Reference: Start-Up - Direct Gas,
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