White Rodgers 50M56U-843 Manuel D’Utilisation

8

White-Rodgers is a division 
of Emerson Electric Co.

The Emerson logo is a  
trademark and service mark 
of Emerson Electric Co.

1

External lockout (exceeded retries)

Failure to sense flame is often caused by carbon deposits on 
the flame sensor, a disconnected or shorted flame sensor lead 
or a poorly grounded furnace. Carbon deposits can be cleaned 
with emery cloth. Verify sensor is not contacting the burner
and is located in a good position to sense flame. Check sensor 
lead for shorting and verify furnace is grounded properly. Verify
gas supply to valve, gas valve in "On" position and appliance 
lighting properly. Verify flame reaches flame sensor during
ignition attempts and gas pressures are correct. 

2

Pressure switch stuck closed

Pressure switch stuck closed. Check switch function, verify 
inducer is turning off. Refer to wiring diagram, terminals PSI / 
PSO.

3

Pressure switch stuck open

Check pressure switch function and tubing. Verify inducer is
turning on and pulling sufficient vacuum to engage switch. 
Refer to wiring diagram, terminals PSI / PSO.

4

Open high temperature limit switch

Verify continuity through limit switch circuit. Refer to wiring
diagram terminals, HLI / HLO. 

5

Flame sensed with gas valve de-energized

Verify the gas valve is operating and shutting down properly.
Flame in burner assembly should extinguish promptly at the
end of the cycle. Check orifices and gas pressure.

6

Open rollout switch 

Verify continuity through rollout switch circuit. Refer to wiring
diagram terminals, RO IN / RO OUT. 

7

Low flame sense current

Low flame sense current is often caused by carbon deposits on 
the flame sensor, a poorly grounded furnace or a mis-aligned 
flame sense probe. Carbon deposits can be cleaned with 
emery cloth. Check or improve furnace and module ground. 
Verify sensor is located in or very near flame as specified
by the appliance manufacturer. Refer to wiring diagram FS 
terminal and GND.

8

Ignitor relay fault

This flash code does not indicate a broken, disconnected or 
shorted ignitor. It indicates the ignitor relay contacts on the 
ignition module are not functioning properly. Replace the 
ignition module. 

Rapid Flash

Reversed polarity

Verify the control and furnace are properly grounded. Check
and reverse polarity (primary or secondary) if incorrect. 

Continuous 

On

Normal operation

No fault

Off 

Control failure

Verify power to the control, replace control if power is at the
control and no lit Red LED