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York TM9V two-stage variable-speed gas furnace · exact showing

York TM9V two-stage variable-speed gas furnace showing 12 red flashes: meaning and exact next steps

12 red flashes means A loose or missing model ID plug. This answer applies only to TM9V*C two-stage variable-speed ECM gas furnaces (96% AFUE) whose control board LED flashes red, green or amber, as listed in York International's installation manual 5402851-UIM-A-0917. The slow flash is two seconds on and two seconds off. Other codes flash for a third of a second on and off, repeated the number of times of the code, with a two-second pause between sets, and they repeat as long as the fault lasts. Other furnace families use other pages.

On the covered York TM9V two-stage variable-speed gas furnace, 12 red flashes means a loose or missing model ID plug. First, note whether the furnace was recently serviced or the control board was recently replaced. Then: the ID plug sets the model settings for the control, so a technician should confirm that the plug is present and seated for this furnace.

Part of York TM9V two-stage variable-speed gas furnace error codes guide

Differential

Likely causes of “York TM9V two-stage variable-speed gas furnace showing 12 red flashes”, and how to tell them apart

  1. 1

    A loose or missing model ID plug

    What separates it The code appears after a board replacement

    How to confirm Technician check of the plug

  2. 2

    A plug not matched to the furnace

    What separates it The furnace runs oddly

    How to confirm Technician check

  3. 3

    A damaged plug connector

    What separates it The plug will not seat

    How to confirm Technician replacement

  4. 4

    A board fault

    What separates it The plug is fine

    How to confirm Technician replacement

  5. 5

    Recent service

    What separates it The furnace was opened

    How to confirm Tell the technician

Before you touch a setting

Record this first — changing settings destroys the evidence

  • That the LED shows twelve red flashes
  • Whether the furnace was recently serviced
  • Whether the board was replaced
  • The model and serial numbers

Try in this order

0 of 8 completed

  1. What to do first

    Reversible

    Note whether the furnace was recently serviced or the control board was recently replaced.

  2. Correct only the documented fault domain

    Reversible

    The ID plug sets the model settings for the control, so a technician should confirm that the plug is present and seated for this furnace.

  3. Turn the furnace off

    Reversible

    At the switch.

  4. Do not open the panels

    Reversible

    The plug is on the board.

  5. Note recent work

    Reversible

    On the furnace.

  6. Tell the technician

    Reversible

    The code and the history.

  7. Record the model number

    Reversible

    From the label.

  8. Call a technician

    Reversible

    To check the plug.

Model-specific

What is true of this model and not of its siblings

A tiny part with a big job
The model ID plug carries settings such as blower speeds and heat ranges for one specific furnace. Without it, the board cannot know how to run.
York's guidance
York gives no separate steps; a technician confirms the plug is present and seated for this furnace.
After a board swap
A replacement board needs the original plug moved across. If it was left behind, the code appears at once.
The right plug
Plugs are not interchangeable between models.
Tell the servicer
Say what work was done before the code appeared.
Safety
The furnace should stay off until the plug is checked.
What the plug holds
The plug is a small jumper connector with a pattern of links that tells the board the model's heating capacity, airflow tables and options. Different York models use different plugs. If the board has none, or the wrong one, it cannot choose speeds or timings.
When the code usually appears
The most common moments are just after a board replacement, after a service visit that unplugged the connector, or after a pest or moisture problem damaged the harness. If one of these applies, tell the technician, who can then go straight to the plug.
Keeping the right parts
Whenever a board is replaced, ask the technician to confirm that the plug was moved from the old board and that the settings match your model. Write down the model number from the rating plate so a later technician can check it.

Stop boundary

When this stops being a self-service repair

  • !Never bypass, jumper or tape over a safety switch
  • !Stop for a carbon monoxide alarm, soot, scorch marks or flame outside the burner compartment
  • !Call a qualified technician for anything behind the furnace's panels
  • !If you smell gas, leave the building and call the gas utility from outside; do not use switches or phones inside

Evidence ledger

Sources behind this answer

01
York International Two Stage Variable Speed ECM Residential Gas Furnaces installation manual, TM9V*C series (5402851-UIM-A-0917)
02
York York furnace diagnostic LED flash codes

Exact questions

Common questions

What does 12 red flashes mean on a York TM9V two-stage variable-speed gas furnace?+

A loose or missing model ID plug.

What is the plug?+

A small connector that tells the board which furnace it controls.

Is it an owner fix?+

No.

Why does it appear after service?+

The plug may not have been refitted.

Wrong device or version?

Match the path before repeating the steps.

Match another device