25
Thermostat Control Model
Troubleshooting
Heater Will Not Fire:
•
Be sure thermostat has a set point higher than the ambient temperature; otherwise heater is in standby
mode.
•
Check if heater gas shut off valve is open.
•
Check heater regulator to determine a gas flow is available.
•
Check high limit switch to be sure they are closed. Use a voltage meter, set on continuity, to be sure the
high limit is working properly.
•
Following the STC-100 thermostat control power cord back to the heater and into the heater control box
(see electrical schematic); check ground wire (green) is connected to ground terminal of heater control
box. Check the power wire (white) is connected to the #1 terminal block. Check that the return power
wire (black) is connected to the #5 terminal block. Use a voltage meter, set on continuity, to be sure the
thermostat is operating properly.
•
Inside the STC-100 thermostat control, check that the ground wire (green) is grounded to the box. Check
the power wire (white) is connected to red wire from the thermostat. Check the return power wire (black)
is connected to black wire from the thermostat. Use a voltage meter, set on continuity, to be sure the
thermostat is operating properly.
Heater Fires But Does Not Cycle Off or Has A Long Cycle:
•
Check to see if the thermostat control bottom is free of any debris; this must be open and not sealed, to
allow air to exit; otherwise a dead space has been created and the thermostat cannot properly sense the bin
temperature.
Caution: Bleed fuel lines before servicing unit. The procedures outlined below are for use only by qualified
service personnel. Use caution when checking electrical components.
Operating Light is Not Coming On.
•
Be sure thermostat has a set point higher than the ambient temperature; otherwise heater is in standby
mode.
•
Confirm incoming power, which should be interlocked with fan, is present. Open up fan control panel and
be sure fan and heater have been interlocked together.
•
Confirm heaters peripherals are working correctly. Connect one lead of voltmeter to neutral at terminal
block. This will remain connected throughout procedure (see electrical schematic pages 28-29).
a.
Check high-limit: Connect lead to terminal block labeled 120. If no voltage is read high-limit is not
working correctly and will need to be replaced.
b.
Check power supply: With switch in the “ON” position, connect voltmeter lead to test both sides of
switch. If no voltage, confirm switch is not functioning.
c.
Check timer: Connect lead to “NO” on timer and wait 45 seconds. If no voltage is present after 45
seconds, replace timer (S224463).
