10
1. Turn the
heater to
position #1
and nothing
happens.
2. The heater
runs for a little
while, but
shuts down. It
won’t come on
again until I
reset the limit
switch.
• Power supply cord
• Burner lock out on the burner flame
safeguard control box is engaged
• Overheat limit switch is tripped
• 24 volt transformer
• Burner motor relay
• Burner sensor
• Heater control unit (HCU)
• Burner orifice is improperly sized
• Incorrect burner manifold pressure
• Restricted airflow
• Overheat limit switch faulty due to loss of
power
• Test for 120 volts between L1 and N on the main terminal block.
• Turn thermostat off and on.
• Reset switch, located on the right hand corner (facing the right hand side of the
unit) .
• Using a volt meter, check for 24 volts AC between ground and one of the “T”
terminals on the burner control box. If less than 24 replace transformer.
• Turn on the heater. Check for 120 volts between ground and both black wires
on the relay. Relay is located in the burner control box under the flame
safeguard control. If less than 105 replace relay.
• On the heater control unit (HCU) disconnect the wires from terminals X10 and
X11. Using an ohm meter, check the resistance between the two wires for a
reading of 8K-15K ohms. Replace sensor if out of range.
• On the main terminal block, check for 120 volts between terminals 8 and N
when the 3-position switch is in the HEAT position. If less than 105 replace HCU.
• For propane, use size .201.
For natural gas, use size .261.
• Use a low pressure gauge (0-15 inches of water column) with a 1/8” NPT inlet.
Install gauge in the pressure tap port located on the output side
of the gas valve. Run the heater. Adjust the pressure by turning the pressure
adjusting screw (located on the input side top of the gas valve) counter
clockwise until the gauge reads 3” W.C.(Propane) & 3.2”W.C.(Nat Gas)
• Check for dirt or ice buildup on the air inlet or blower wheel. If using duct on
the air outlet, insure the back pressure does not exceed a static pressure of .25”
W.C. Check with low pressure gauge if necessary (0-15 inches of water column).
• Adhere to the proper shut down procedures.
Power must remain at the unit until it cools down fully. Blower will shut down on
its own when cool. Test overheat limit switch for continuity between the two
male terminals at room temperature. Replace if overheat limit switch
fails test.
VG175 TROUBLESHOOTING
Symptom Possible Causes Possible Solutions
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