York Furnace Error Codes: Red, Green and Amber Flashes

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

York Furnace Error Codes: Red, Green and Amber Flashes

Short answer

York's control light has three colours. Green is normal and amber means it is running. 4 or 5 amber means held back, often by a dirty filter or a blocked vent. Red is a fault. 3 red is the pressure switch, 4 red a limit and usually airflow, 7 red a lockout after failing to light, and 1 red means flame with the gas valve off, which is the one to shut the gas off for.

York furnaces use one light on the control board, seen through a small window in the lower door, and it flashes in three colours. The colour tells you how worried to be, and the count tells you where to look.

Everything on this page comes from York’s own installation manual 561276-UIM-A-0310 for the TM9M modulating furnace, published by Johnson Controls, which makes York. Other York models use the same colour system with a few codes of their own, so the label in your own furnace door has the final word.

Before you start

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

Gas or electric? These are gas furnace codes.

How to count. York says the light flashes on and off quickly, a quarter second each, the number of times of the code, then goes off for two seconds before repeating.

Read it through the window first. The light is visible through the clear port in the lower door.

Two codes that mean shut the gas off, not reset. 1 red flash: flame with no power to the gas valve. York says a gas valve that is slow to close or leaks gas through to the burners can cause it. Turn the furnace off and turn the gas off to it.

5 red flashes: the rollout switch. York says it is manually reset, and to check combustion air, the inducer, and for heat exchanger failure or a burner problem before resetting: what a rollout switch is telling you.

York’s own warning: never bypass a safety control and never adjust the pressure switch to make the furnace run.

What the colours mean

Green is normal, amber is running or held back, red is a fault. Count the flashes between the two second pauses.

Check 1Free, two minutes

Read the colour, then count

No light. York says there is no 24 volt power to the board. Check the 24 volt fuse on the board, the breaker for the furnace and the transformer.

Green. One green flash is normal with no call for heat. Two green means no error codes are stored.

Amber, normal running. One amber is cooling, two amber is heating, three amber means the burner is finishing after the thermostat was satisfied.

Four amber: held back by airflow. York says heating capacity is reduced because of a restriction in the circulating air. Check for a dirty filter or closed registers.

Five amber: held back by the vent. Capacity reduced because of a restriction in the combustion air or vent. York names a blocked vent or air pipe, or a clogged condensate drain.

Rapid amber. Low flame sense current. York says check for a dirty or mislocated flame sensor rod.

Steady red. A control fault, or 24 volts present without 115 volts.

Every red code

Red flashes	What York says it means	Check first
1	Flame present with no power to the gas valve	Shut the gas off
2	Pressure switch closed when it should be open	The pressure switch
3	Pressure switch open when it should be closed	Vent, drain, hoses, switch
4	Primary or auxiliary limit open	Filter, blower speed, duct size
5	Rollout switch open	Why flame rolled out, then reset
6	Gas valve communication error	Wiring and pressure hoses
7	Lockout, no ignition after three tries	Gas supply, igniter, flame sensor
8	Lockout, flame lost five times in one cycle	Flame sensor, gas pressure
9	Reversed line polarity or improper grounding	Electrician
10	Gas valve circuit shorted	Gas valve wiring
11	Main blower failure, limit open over five minutes	Blower motor or wheel
12	ID plug not present or loose	The plug on the board

The codes you can often clear yourself

Four codes with a free first check. Two of them are amber warnings that turn red if they are left.

Check 2

Work the free check for your code

4 amber, and 4 red after it: airflow. York lists a dirty filter first. Change it, open every register, and watch a cycle: why a furnace overheats and cuts out.

5 amber and 3 red: venting. York names a blocked vent or air pipe and a clogged condensate drain. Look outside for snow, ice or a nest in the pipes, then at the drain trap: the five places to look.

Rapid amber and 8 red: the flame sensor. York gives normal flame sense current as about 3.7 microamps, with the warning starting at 1.5. A dirty sensor is the usual cause: how to clean a flame sensor safely.

7 red: no ignition. York says the control tries three times, locks out for an hour, then tries again. Check the gas is on at the furnace first.

No light at all. The breaker, the furnace switch, and the small 24 volt fuse on the board.

When it needs a technician

Check 3

Know when to stop

1 red and 10 red. Gas valve faults.

2 red. A pressure switch reading closed when it should be open.

6 red, 9 red, 12 red and steady red. Wiring, grounding, the ID plug or the control board.

11 red. York says the main limit stayed open for over five minutes, pointing at a failed blower motor or wheel.

The stored codes. York’s board keeps the last five codes even through a power cut, read with a Last Error button with no call from the thermostat. York says only a qualified technician should use it.

Questions people ask

What does 4 red flashes mean on a York furnace?

A primary or auxiliary limit switch has opened. York lists a dirty filter, an undersized duct system, the blower speed, the firing rate or a faulty blower motor, and also a blown fuse on the board.

My York flashes amber. Is that a fault?

One to three amber flashes are normal running. Four and five amber mean it is running but held back by airflow or venting, and rapid amber is a weak flame signal.

How long is the York lockout?

One hour, according to York, after three failed tries to light or five flame losses in one cycle. It then tries again by itself.

Do Coleman and Luxaire furnaces use the same codes?

Johnson Controls makes furnaces under more than one name, and many share controls. The label in your own furnace door confirms the codes yours uses.

What does two green flashes mean?

No error codes stored. It is what you see after checking the history on a furnace with nothing wrong.

Can I clear the code by cutting the power?

It often brings the heat back. The stored codes stay in memory anyway, so write the code down for whoever comes out.

Sources: York (Johnson Controls) installation manual 561276-UIM-A-0310 for the TM9M furnace