White-Rodgers 50M56U Flash Codes and Fault Recall

By Ray Bennett · Updated 2 October 2026 · 5 min read · Checked against the maker’s manual

White-Rodgers 50M56U Flash Codes and Fault Recall

Short answer

On the White-Rodgers 50M56U universal furnace board, a steady light is normal and no light means the control has failed. Flashes count out a fault: 1 a lockout, 2 and 3 the pressure switch, 4 the high limit, 5 flame with the gas valve off, 6 the rollout switch, 7 a weak flame signal, 8 the igniter relay. Rapid flashing is reversed polarity.

The White-Rodgers 50M56U is a universal single stage hot surface ignition control, a replacement board fitted to furnaces of many brands. Its light is on steady when all is well, flashes a count when there is a fault, and can play back the last five faults at the press of a button.

Everything on this page comes from White-Rodgers’ own installation instructions for the 50M56U-843 kit. Be careful with its older cousin: on the White-Rodgers 50A55 the same lights mean different things, so check the model number printed on the board first.

Before you start

What to carry: a torch and a pen. Ten minutes.

Gas or electric? A gas furnace control, for natural gas or propane.

How to count. White-Rodgers says each flash lasts about a quarter of a second and each pause about two seconds.

Check the model. The number is printed on the board. This page is for the 50M56U only: the 50A55 codes, which read differently.

Two codes where you stop. 5 flashes: flame with the gas valve off. White-Rodgers lists it as flame sensed with the gas valve de-energized. Turn the furnace and the gas off and call a technician.

6 flashes: the rollout switch. It trips when flame comes out of the burner area. White-Rodgers says you may need to reset it after a lockout, but find out why it tripped first: what a rollout switch is telling you.

What the light means

On the 50M56U, a steady light is normal. Two codes, flame with the valve off and the rollout switch, are the ones to stop at.

Check 1Free, two minutes

Read the light

On steady. White-Rodgers calls it normal operation.

Off. White-Rodgers says that if the failure is internal to the control, the light stays off, and the control must be replaced because it is not field repairable. Check first that the furnace has power at all: the breaker and the furnace switch.

1 flash, system lockout. The ignition retries have been used up without lighting.

2 and 3 flashes. The pressure switch stuck closed, or stuck open.

4 flashes. The high temperature limit switch is open, usually from overheating.

7 flashes. A low flame sense signal. The flame is there but the sensor barely sees it.

8 flashes. An igniter relay fault on the board.

Rapid flashing. Reversed polarity on the line voltage.

Two White-Rodgers boards, two meanings

The 50M56U and the 50A55 disagree about a steady light and about 5 and 6 flashes. Read the model number first.

Check 2Free, one minute

Make sure you have the right table

A steady light. Normal on the 50M56U, a failed control on the 50A55.

5 and 6 flashes. On the 50M56U, 5 is flame with the valve off and 6 is the rollout switch. On the 50A55, 5 is the rollout switch and 6 is polarity or ground.

Rapid flashing. Reversed polarity on the 50M56U, but flame with no call for heat on the 50A55.

The checks that are yours

Check 3

Work the free checks

1 flash: the gas. Is the gas valve on the furnace on and the line shut-off open? On propane, is there gas in the tank: why a furnace clicks but will not light.

3 flashes: the vent and hoses. A blocked vent, a split or water-filled hose, or the inducer: the places a pressure switch fault hides.

4 flashes: airflow. Change the filter and open every register: why a furnace overheats and cuts out.

7 flashes: the flame sensor. A dirty sensor rod is the common cause: how to clean a flame sensor safely.

Fault recall and resets

Check 4Free, five minutes

Read the history, reset once

Read the last five faults. With no call for heat or cooling, press the FAULT RECALL button for about two seconds until the light goes off, then release it. After two seconds the stored codes play back, newest first, with a two second pause between them. White-Rodgers says the control ignores any new call for heat, cooling or fan while it does.

Erase them. Hold FAULT RECALL for five to ten seconds until the light flashes rapidly, then release. The light goes off for two seconds, then back on.

Reset a lockout. White-Rodgers gives three ways: interrupt the call for heat at the thermostat, interrupt the 24 volt power for at least a second, or wait. After one hour of lockout, the control resets itself and runs a 60 second purge.

The exception. White-Rodgers says the thermostat reset does not work if flame was sensed with the gas valve off.

Questions people ask

What does 3 flashes mean on a White-Rodgers 50M56U?

The pressure switch is stuck open. Check the vent for blockage, the hose for splits or water, and whether the inducer runs.

Is a steady light normal?

On the 50M56U, yes: White-Rodgers calls it normal operation. On the 50A55, a steady light means the control has failed.

What does 8 flashes mean?

An igniter relay fault on the control board. That points at the board rather than the igniter itself.

How do I see the last faults?

With no call for heat or cooling, hold FAULT RECALL about two seconds until the light goes off, then let go. The last five codes play back, newest first.

What does rapid flashing mean on a 50M56U?

Reversed polarity on the line voltage. That is an electrician’s fix.

What does 5 flashes mean on a 50M56U?

Flame sensed with the gas valve de-energized. The control sees flame when the valve should be closed, so turn the gas off and call a technician. On a 50A55, 5 flashes means something else.

Why is the light off?

Check the furnace has power first. If it does, White-Rodgers says an internal failure leaves the light off, and the control must be replaced.

Sources: White-Rodgers installation instructions for the 50M56U-843 universal single stage HSI integrated furnace control kit