- 17 -
Status Code 3
LOW PRESSURE SWITCH DID NOT CLOSE OR REOPENED - This status code can occur as a result of the low pressure
switch LPS not making or the low gas pressure switch LGPS opening. Regardless of which switch is open, the modulating
furnace control will operate under the scenarios shown below. Keep in mind that whenever the modulating furnace control
shuts unit down, gas remains off or shuts off immediately and inducer continues running for 15 seconds. If the low
pressure switch LPS opens within 5 minutes after ignition the next heating cycle will be restricted to maximum-heat.
- MINIMUM, INTERMEDIATE, OR MAXIMUM HEAT
1. PREPURGE - If the low pressure switch LPS does not make within 45 seconds after a call for heat is initiated and the medium pressure
switch MPS or high pressure switch HPS does not make the modulating furnace control will flash status code 3, shut the unit down, wait 2
minutes, stop flashing status code 3, and restart the heating cycle.
2. AFTER IGNITION - If the low pressure switch LPS opens after the burners ignite the modulating furnace control starts flashing status
code 3, shuts unit down, turns on the blower, or continues to operate the blower, at minimum heat airflow for the selected blower off-delay
period, stops flashing status code 3, and restarts the heating cycle.
STEP
ACTION
YES
NO
GO TO
1.
Turn power off, remove both doors, and disconnect communication connector PL7 (if used)
or the R thermostat lead (if used) from the furnace control board.
2
2.
Turn power on and depress door switch. Use a piece of tape to hold switch closed.
3
3.
Jumper R and W/W1 thermostat terminals.
4
4.
Observe operation of the inducer motor for 1 minute before proceeding to the next step.
5
5.
Does status code 3 flash?
9
6
6.
Does a different status code flash?
7
35
7.
Go to page number indicated in the Index for the section covering the status code.
INDEX
8.
Go to page number indicated in Index for CLEANUP AND START-UP INSTRUCTIONS.
INDEX
9.
Is 24-vac across YELLOW wire on the low pressure switch LPS and C
OM
-24V on
modulating furnace control?
14
10
10.
Is 24-vac across connector terminal PL1-2 and C
OM
-24V on modulating furnace control?
11
13
11.
PL15 is not connected or you have an open wire or bad terminal on the YELLOW wire from
the modulating furnace control to the low pressure switch LPS.
12
12.
Repair or replace the main wire harness.
8
13.
Replace the modulating furnace control.
8
14.
At start of cycle as inducer is ramping up, does low pressure switch LPS make then break?
15
17
15.
The problem is either a sag in vent pipe or a clogged drain trap or line. Also check for
improperly plumbed drain tubing within furnace.
16
16.
Fix problem.
8
17.
Does status code 3 flash once then flash status code 4 + 3?
18
46
18.
On propane installations the propane tank may be low otherwise you may have a loose
connection between the low pressure switch LPS and the modulating furnace control. This
includes the ORANGE wire interconnecting the low pressure switch LPS to the modulating
furnace control.
16
19.
You have excessive restriction in the vent pipe. Also, check for proper vent sizing for
installation.
16
20.
Were there any leaks or blockages found in steps 46-49?
16
21
21.
Turn power off and disconnect jumper wire across R and W/W1 thermostat terminals.
22
22.
Connect 1 side of slope manometer with a tee to collector box pressure tap. Refer to pressure
check diagram in Appendix C.
23
23.
Turn power on and jumper R and W/W1 thermostat terminals.
24
24.
Do you have at least 0.87 in. wc pressure drop across heat exchangers when fault occurs?
25
26
25.
Replace the pressure switch assembly.
8
26.
Is inducer motor rotating in direction indicated on the inducer housing?
28
27
27.
Replace inducer control (if you have 2 piece design) or inducer motor assembly.
8
28.
Turn power off.
29
29.
Is inducer wheel okay?
31
30
30.
Replace inducer motor assembly.
8
31.
Is the inducer wheel properly mounted to the inducer motor shaft?
32
16
32.
Does the inducer wheel turn freely?
19
16
33.
The problem is caused by reversed vent and combustion-air pipes or some other moist air
entering combustion-air pipe.
16
440 08 4001 00
