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

York TM9V two-stage variable-speed gas furnace showing 2 red flashes: meaning and exact next steps

2 red flashes means The pressure switch is closed when it should be open. The control confirms the switch contacts are open at the beginning of each heat cycle and will not let the ignition sequence continue if they are closed. 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, 2 red flashes means the pressure switch is closed when it should be open. The control confirms the switch contacts are open at the beginning of each heat cycle and will not let the ignition sequence continue if they are closed. First, note that the code appears at the start of a heating call.

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 2 red flashes”, and how to tell them apart

  1. 1

    A pressure switch stuck closed

    What separates it The code appears at the start of a heating call

    How to confirm Technician testing

  2. 2

    A pressure transducer fault

    What separates it Readings are wrong at rest

    How to confirm Technician testing

  3. 3

    A shorted wire to the switch

    What separates it Switch always closed

    How to confirm Technician inspection

  4. 4

    A tube with water in it

    What separates it The switch reads wrongly

    How to confirm Technician draining

  5. 5

    A control fault

    What separates it Parts test well

    How to confirm Technician diagnosis

Before you touch a setting

Record this first — changing settings destroys the evidence

  • That the LED shows two red flashes
  • That it appears at the start of the call
  • Recent service
  • Whether the inducer starts

Try in this order

0 of 8 completed

  1. What to do first

    Reversible

    Note that the code appears at the start of a heating call.

  2. Correct only the documented fault domain

    Reversible

    York's manual says to check for a faulty pressure switch or miswiring. That is technician work.

  3. Turn the thermostat off

    Reversible

    Then call for heat again.

  4. Note when the code appears

    Reversible

    Start of the call?

  5. Listen for the inducer

    Reversible

    Does it start?

  6. Do not tamper with the switch

    Reversible

    It is a safety part.

  7. Record the date

    Reversible

    And the weather.

  8. Call a technician

    Reversible

    For the switch and transducer.

Model-specific

What is true of this model and not of its siblings

Open before start
Before every cycle the control checks that the pressure switch is open, which shows it is not stuck. A closed switch at rest is a fault.
York's guidance
York says to check the pressure switch and the pressure transducer, both of which are sensing and safety parts.
A stuck switch
Dirt, corrosion or condensate can hold the contacts together.
A wiring cause
A pinched wire may short the circuit.
Why a technician
Replacing a safety switch with a wrong part is a danger.
Heat in the meantime
Use safe alternatives and keep the house warm enough to protect pipes.
A check you never see
Every time the thermostat calls for heat, before the inducer starts, the control looks at the pressure switch and expects it to be open. The check happens in a fraction of a second. If the switch is closed, the control refuses to proceed, and you see two flashes.
Hose and tube clues
The switch is connected to the furnace by a small rubber tube. A tube that has collapsed, filled with water or bent can hold the switch in the wrong state. A technician checks the tube, the tap on the vent and the switch itself.
Why safety parts are not swapped by guess
A pressure switch is rated for a specific pressure. A part with the wrong rating may close at the wrong time and allow the furnace to run with a blocked vent. Ask that the replacement match York's part number for your model.

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

The pressure switch is closed when it should be open. The control confirms the switch contacts are open at the beginning of each heat cycle and will not let the ignition sequence continue if they are closed.

What do two red flashes mean on a York TM9V?+

The pressure switch is closed when it should be open.

Why does that matter?+

The control must see the switch open before the inducer starts.

What tests it?+

A technician's meter.

Can I replace it?+

No, call a technician.

Wrong device or version?

Match the path before repeating the steps.

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