508134-01
Issue 2045
Page 16 of 53
Problem
Corrective Action
Pressure switch stuck closed
Check that the pressure switch is open without the combustion air inducer
operating. Replace if defective.
Pressure switch does not close due to obstruction in
vent pipe
Check for restricted vent. Remove all blockage.
Check for proper vent sizing. See Table 11A through Table 11B.
Pressure switch does not close due to incorrect
routing of the pressure switch tubing
Check that the pressure switch tubing is correctly routed. Correctly route
pressure switch line.
Pressure switch does not close due to obstructions in
the pressure switch line
Remove any obstructions from the the pressure switch line and/or taps
Pressure switch tubing damaged
Check pressure switch tubing for leaks. Replace damaged tubing if
necessary.
Condensate in pressure switch tubing
Check pressure switch tubing for condensate. Remove condensate from
tubing.
Pressure switch does not close due to a low
differential pressure across the pressure switch
Check the differential pressure across the pressure switch.
Check for restricted inlet vent. Remove all blockage.
Check for proper vent sizing and run length. See Table 11A through Table
Wrong pressure switch installed in the unit, or
pressure switch is out of calibration
Check that the correct pressure switch is installed in the unit. Replace
pressure switch if necessary.
Miswiring of furnace or improper connections at
pressure switch
Check for correct wiring and loose connections. Correct wiring and/or replace
any loose connections.
Pressure switch failure
If all the above modes of failure have been checked, the pressure switch
may have failed. Replace pressure switch and determine if unit will operate.
Damaged condensate trap
Check trap for any cracks or damage and replace if necessary.
Cold end header box does not drain properly
Check that the furnace is set properly with a slight tilt (0 - 1/2”) towards the
front if necessary. See furnace installation instruction.
Air leakage around the combustion air inducer gasket
Check gasket and replace if necessary.
Air leakage around the cold end header box gasket
Check gasket and replace if necessary.
Damaged cold end header box tubing
Check tubing and replace if necessary.
Table 7. Pressure Switch Troubleshooting Guide
Figure 12. Electronic Ignition
DEMAND
CAI
GAS VALVE
15
ON
OFF
38
IGNITOR
34
1
Pre -Purge
Ignitor Warm-up
Trial for
Ignition
Post
Purge
5 SEC
80
*Blower on time will be 30 seconds after flame is sensed. Blower off time will depend on “OFF TIME” Setting.
INDOOR BLOWER
Blower “On”*
Delay
