Thomas & Betts LDAP 1200 Manuale Utente

The integrated circuit board monitors the operation of the heater and includes two
LED signal lights that indicate normal operation and various abnormal conditions. If
the heater fails to operate properly, check this signal to determine the cause and/or to
eliminate certain causes. See operating sequence in Paragraph 19.
Do not attempt to repair the DSI integrated control module; the only field replaceable
component is the fuse.

IMPORTANT: When using a
multimeter to troubleshoot the
24 volt circuit, place the meter’s
test leads into the 5 or 9 pin
connectors located on the
ignition control. Do not remove
connectors or terminals from
the electrical components.
Doing so can result in misinter-
preted readings due to the
ignition control board’s fault
mode monitoring circuits.

Steady On Normal Operation - No call for heat. Steady On

Flame is sensed.

Fast Flash Normal Operation - Call for heat.

Slow Flash Weak flame (current below 

1.0 microamps ±50%)

1 Flash

System Lockout (failed to detect or 
sustain flame)

Fast Flash

2 Flash

Main combustion air pressure 
switch or heat section pressure 
switch does not close with 30 
seconds of venter being energized.

3 Flash

Limit or high limit switch open.

4 Flash

Main combustion air pressure 
switch or heat section pressure 
switch is closed before venter is 
energized.

Steady Off Blown fuse; No power; or Defective 

board

Undesired flame (valve 
open and no call for heat). 

See FIGURE 22, page 34, for location. Use a voltmeter to verify
that there are 24 volts output from the transformer. If the trans-
former is not functioning, it must be replaced. Use a replacement
transformer identical to the factory-installed model.

A manual reset high limit control is located at the top of each heat
section. Do not reset high limit control without correcting the prob-
lem. If it is determined that the limit control needs replacing, use
only a factory-authorized replacement part that is designed for the
size of heater.

Check the complete vent system at least once a year. Inspection should include all
joints, seams, and the vent terminal cap. Clean openings. Replace any defective parts.

See FIGURE 22, page 34, for location. Check the wiring connec-
tions and the adjustment knob.

If it is determined that the destratification fan control needs re-
placing, use only a factory-authorized replacement part that is de-
signed for the heater.

If it is determined that the automatic reset limit control needs re-
placing, use only a factory-authorized replacement part that is de-
signed for the size of heater.

For approximate limit location, see FIGURE 22, page 34.