Fig. 60 – Troubleshooting Guide
25 INVALID MODEL SELECTION OR
SETUP ERROR – If status code 25 only
flashes 4 times on power-up the control is
missing its model plug PL4 and is
defaulting to the model selection stored in
memory. If status code 25 flashes
continuously it could indicate any of the
following:
- Model plug PL4 is missing and there is
no valid model stored in permanent
memory. This will happen if you forget
to install the model plug PL4 on a
service replacement control.
- Thermostat call with SW1-1 ON.
- Thermostat call with SW1-6 ON.
- SW1-1 and SW1-6 both ON.
- Two different furnace models twinned.
- If replacing a control, be sure to use
correct version (V##) located on control
board) Models supported should be
listed.
31 HIGH-HEAT PRESSURE SWITCH OR
RELAY DID NOT CLOSE OR
REOPENED - Check for:
- Control relay may be defective.
- Gas valve is miswired.
- See status code 32.
21 GAS HEATING LOCKOUT – Turn off
power and wait 5 minutes to retry. Check
for:
- Stuck closed gas valve relay on control.
- Miswire or short to
as valve.
23 PRESSURE SWITCH DID NOT OPEN –
Check for:
- Obstructed pressure tube.
- Pressure switch stuck closed.
24 SECONDARY VOLTAGE FUSE IS OPEN
Check for:
- Short circuit in secondary voltage (24V)
wiring including thermostat leads.
Disconnect thermostat leads to isolate
short circuit.
32 LOW-HEAT PRESSURE SWITCH DID
NOT CLOSE OR REOPENED – If open
longer than 5 minutes, inducer shuts off
for 15 minutes before retry. If opens
during blower on-delay period, blower will
come on for the selected blower off-delay.
Check for:
- Proper vent sizing.
- Low inducer voltage (115V).
- Low inlet gas pressure (if LGPS used).
- Inadequate combustion air supply.
- Disconnected or obstructed pressure
tubing.
- Defective inducer motor.
- Defective pressure switch.
- Excessive wind.
- Restricted vent.
33 LIMIT CIRCUIT FAULT – Indicates the
limit, draft safeguard, flame rollout, or
blocked vent switch* (if used) is open or
the furnace is operating in high-heat only
mode due to 2 successive low-heat limit
trips. Blower will run for 4 min. or until
open switch remakes whichever is longer.
If open longer than 3 min., code changes
to lockout #13. If open less than 3 min.
status code #33 continues to flash until
blower shuts off. Flame rollout switch and
BVSS requires manual reset. Check for:
- Dirty filter or restricted duct system.
- Loose blower wheel.
- Defective switch or connections.
- Inadequate combustion air supply
(flame rollout switch open).
- Restricted vent.
- Proper vent sizing.
- Excessive wind.
- Blower motor not operating
34 IGNITION PROVING FAILURE – If flame is
not sensed during the trial for ignition
period, the control will repeat the ignition
sequence 3 more times before lockout #14
occurs. If flame signal is lost during the
blower on-delay period, blower will come on
for the selected blower off-delay. Check
the following items first before proceeding
to the next step.
- Gas valve turned off.
- Manual shut-off valve.
- Green/Yellow wire MUST be connected
to furnace sheet metal.
- Flame sensor must not be grounded.
To determine whether the problem is in the
gas valve, igniter, or flame sensor the
system can be operated in component test
mode. To check the igniter remove the R
thermostat connection from the control,
reset power, and put setup switch SW1-6 in
the ON position to start the component test.
Does the igniter glow orange/white by the
end of the 15 second warm-up period?
Unplug igniter harness from control and
repeat component test by turning setup
switch SW1-6 OFF and then back ON.
Check for 115V between pin 3 and
NEUTRAL-L2 on the control. Was 115V
present for the 15 second period?
Check connections and retry.
If current is near typical value
(4.0-6.0 nominal) and burners
will not stay on, repeat check
in high-heat. If burners will
still not stay on replace
control. If burners operate in
high-heat then switch to low-
heat, check manifold
pressure. If OK, check
burner carryover and flame
sensor location.
Clean flame sensor with fine steel wool
and recheck current. Nominal current is
4.0 to 6.0 microamps.
Is current near typical value? Replace electrode.
Will main burners ignite and stay on? Replace furnace control.
Fixed.
NO
YES
YES
YES
NO
NO
45 CONTROL CIRCUITRY
LOCKOUT Auto-reset
after 1 hour lockout due
to:
- Flame circuit failure.
- Gas valve relay stuck
open.
- Software check error.
Reset power to clear
lockout. Replace control
if code repeats.
Replace furnace control.
Check for continuity in the
harness and igniter. Replace
defective component.
Reconnect the R thermostat lead and set
thermostat to call for heat. Connect
voltmeter across gas valve connections.
Does gas valve receive 24V?
Does gas valve open and allow gas to
flow?
Do the main burners ignite?
Do the main burners stay on?
Allow blower to come on and
repeat test to check for
intermittent operation.
Check that all gas valves are
turned on. Replace valve.
Check connections. If OK,
replace control.
Check for:
- Inadequate flame carryover
or rough ignition.
- Low inlet gas pressure.
- Proper firing rate.
- Blocked or incorrect carry-
over gap. (.045” nominal)
Repeat call for heat and check flame
sensor current during trial for ignition
period. Is the DC microamps below 0.5?
YES
YES
YES
YES
YES
NO
NO
NO
NO
NO
NO
43 LOW-HEAT PRESSURE SWITCH
OPEN WHILE HIGH-HEAT
PRESSURE SWITCH IS CLOSED -
Check for:
- Low-heat pressure switch stuck
open.
- Disconnected or obstructed
pressure tube.
- Miswired pressure switches.
- Low inlet gas pressure (if LGPS
used).
* Blocked vent switch used in Chimney Adapter Kit
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