Lennox SIGNATURE SLP99UHV Installation Instructions Manual page 64

Troubleshooting: Heating Sequence of Operation (continued)
CALL FOR HIGH FIRE WITH TWO-STAGE THERMOSTAT
2
1
2 Stage
Thermostat
1st Call
for High
Fire?
YES NO
2nd Stage
Recognition Delay
(30 Seconds)
Combustion Air Inducer ON
(100% Rate Speed)
High
Pressure Switch
NO
Closes Within
10 Seconds?
YES
Adjust Indoor
Blower to
Appropiate speed
Wait for Call for Heat Satisfied
3A
System will always light at 70% even if 2nd stage call for heat is in place
1
If the high pressure switch does not close within 5 attempts, the system
2
will operate at low fire for the remainder of the call for heat at request
Increase Combustion
Error Code
Air Inducer Speed Flashes
if Not at 100%
Rate Speed
Page 64
Wait 5
Minutes