Secondary Limit Control
The secondary limit control is located on the top of the blower
scroll assembly. This control opens when elevated temperatures
are sensed. Elevated temperatures at the control are normally
caused by blower failure. The reason for the opening should be
determined and repaired prior to resetting.
If the power to the unit is interrupted during the heating cycle, it
may cause the secondary limit control to trip. Once the blower
compartment temperature drops below the limit reset
temperature, the limit will automatically reset.
Secondary Limit Control
A. Secondary limit control
B. Back of unit
1. Close the manual gas shutoff valve external to the unit.
2. Turn off the electrical power supply to the unit.
3. Set the room thermostat to its lowest possible setting.
4. Remove the heat exchanger door on the side of the unit by
removing the screws.
IMPORTANT: This unit is equipped with an ignition device which
automatically lights the main burner. Do not try to light burner by
any other method.
5. Move the gas control valve switch to the OFF position.
NOTE: Do not force the switch to turn.
6. Wait 5 minutes to clear out any gas.
7. Check for a gas odor around the unit, including near the
ground because some types of gas are heavier than air.
IMPORTANT: If you have waited 5 minutes and you do smell
gas, immediately leave the building and call your gas supplier or
the fire department from a neighbor's house.
8. If you have waited 5 minutes and there is no gas odor, move
the gas control valve switch to the On position.
9. Replace the heat exchanger door on the side of the unit.
10. Open the manual gas shutoff valve external to the unit.
11. Turn on the electrical power supply to the unit.
12. Set the thermostat to the desired setting.
Gas Control Valve—White-Rodgers 35G54
Gas supply pressure and manifold pressure with the burners
operating must be as specified on the rating plate.
Gas inlet pressure must be checked and adjusted in accordance
to the type of fuel being consumed.
With Power And Gas Off:
1. Connect a water manometer or adequate gauge to the inlet
With Power And Gas On:
2. Put unit into heating cycle and turn on all other gas
Inlet Gas Supply Pressure
NOTE: Inlet gas pressure must not exceed the maximum value
If operating pressures differ from the Inlet Gas Supply Pressure
chart, make necessary pressure regulator adjustments, check
piping size, etc., and/or consult with local utility.
A. Outlet pressure boss
B. High-fire regulator adjust tower
C. Regulator vent
D. Low-fire regulator adjust tower
E. Coaxial coil terminal (M)
Gas Manifold Pressure
Measurement and Adjustment
Gas Supply And Manifold Check
Gas Inlet Pressure Check
pressure tap of the gas control valve. Inlet gas pressure can
also be measured by removing the cap from the dripleg and
installing a predrilled cap with a hose fitting.
F. Common terminal (C)
G. High-fire coil terminal (HI)
H. On/Off switch
I. Inlet pressure boss
Minimum: 5.0" W.C.
Maximum: 10.0" W.C.
Minimum: 11.0" W.C.
Maximum: 13.0" W.C.