On the covered York YP9C modulating gas furnace, 6 red flashes means gas valve communication error. First, cycle the furnace's power off and back on once, then note whether the code returns. Then: a gas-valve communication error means the control and the valve have stopped talking. If it returns after a power cycle, the valve, its wiring or the board is at fault and needs a technician.
Differential
Likely causes of “York YP9C modulating gas furnace showing 6 red flashes”, and how to tell them apart
- 1
A gas valve communication error
What separates it The furnace stops with six red flashes
How to confirm York names it a gas valve communication error
- 2
A loose valve connector
What separates it The code appears after the furnace was serviced
How to confirm Technician inspection
- 3
A failed valve
What separates it The code returns after a power cycle
How to confirm Technician replacement
- 4
A control board fault
What separates it The valve tests well
How to confirm Technician replacement
- 5
A power glitch
What separates it The code clears after one power cycle
How to confirm Watch the next cycles
Before you touch a setting
Record this first — changing settings destroys the evidence
- That the LED shows six red flashes
- Whether the code returns after a power cycle
- Any recent service or storm
- The model number
Try in this order
0 of 8 completedWhat to do first
ReversibleCycle the furnace's power off and back on once, then note whether the code returns.
Correct only the documented fault domain
ReversibleA gas-valve communication error means the control and the valve have stopped talking. If it returns after a power cycle, the valve, its wiring or the board is at fault and needs a technician.
Turn the furnace off
ReversibleAt the switch.
Wait one minute
ReversibleThen turn it on.
Watch one full cycle
ReversibleDoes the code return?
Note the date and time
ReversibleIf it returns.
Do not open the burner area
ReversibleIt is technician work.
Call a technician
ReversibleIf it returns.
Model-specific
What is true of this model and not of its siblings
- A modulating furnace
- The YP9C modulates its heat, so the control talks to the gas valve with signals, rather than only switching it on and off. A communication error means that conversation failed.
- When it returns
- A single power cycle is the only home step. If the code returns afterwards, the valve, its wiring or the board is at fault and needs a technician.
- A one-off
- Storms and power flickers can produce a stray error. If it clears and does not return for weeks, record the date and carry on.
- What the technician tests
- Valve wiring, valve coil, board output and the 24 volt supply, with a meter.
- Parts and cost
- Ask for a quote that names the part before you agree to a replacement.
- While you wait
- Use another heat source safely, and never run a fuel heater indoors without ventilation.
- Why modulation changes things
- A single-stage furnace opens its valve fully or not at all. A modulating furnace adjusts the valve through many steps, which saves energy and keeps the house steady. The control and the valve exchange signals to do this, and a fault in that exchange stops the furnace rather than risk running without control.
- A careful power cycle
- Turn off the furnace's power switch, wait a minute and turn it on. Do not do this repeatedly, which can mask a failing component and wears out contacts. If the code returns, record the time and say whether the furnace had run for a while first.
- Questions to ask the technician
- Which part failed, the valve, the wiring or the board. Whether the repair is covered by a warranty. Whether anything else was found. Keep the invoice with the model and serial numbers, since parts warranties often depend on them.
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
Exact questions
Common questions
What does 6 red flashes mean on a York YP9C modulating gas furnace?+
Gas valve communication error.
Does cycling the power help?+
Once, to see if it clears.
Is this an owner repair?+
No.
Is the furnace safe to run?+
Not if the code returns; call.