On the covered York YP9C modulating gas furnace, 8 red flashes means lockout due to too many flame recycles. The code occurs if flame is lost five times during a single heating cycle. The control locks out for 1 hour and then tries again. First, watch whether the burners light, hold for a time and then go out, and count how many tries the furnace makes.
Differential
Likely causes of “York YP9C modulating gas furnace showing 8 red flashes”, and how to tell them apart
- 1
A dirty flame sensor
What separates it Burners light then go out repeatedly
How to confirm A technician cleans the sensor
- 2
Low gas pressure
What separates it Flame is weak or lost
How to confirm Technician measurement
- 3
A faulty gas valve
What separates it Flame cuts out during the cycle
How to confirm Technician testing
- 4
A draft or vent problem that blows the flame out
What separates it Flame loss in wind
How to confirm Check the outside terminations
- 5
A control fault
What separates it The pattern repeats with good parts
How to confirm Technician diagnosis
Before you touch a setting
Record this first — changing settings destroys the evidence
- That the LED shows eight red flashes
- Whether burners light and then go out
- How often the lockout repeats
- Whether other gas appliances work
Try in this order
0 of 8 completedWhat to do first
ReversibleWatch whether the burners light, hold for a time and then go out, and count how many tries the furnace makes.
Correct only the documented fault domain
ReversibleYork names a faulty gas valve, low gas pressure and a dirty flame sensor as the likely causes on the modulating YP9C; measuring gas pressure and testing the valve are technician work.
Note the burner behavior
ReversibleDo they light and then go out?
Wait for the lockout to end
ReversibleYork says one hour.
Check other gas appliances
ReversibleTo rule out a supply problem.
Look outside
ReversibleFor a blocked vent or intake.
Do not reset repeatedly
ReversibleEach lockout is a safety response.
Call a technician
ReversibleFor the sensor, valve and pressure.
Model-specific
What is true of this model and not of its siblings
- How the control counts
- The control lights the burners, proves flame with a sensor, and if the flame is lost it tries again. After five losses in one cycle it stops for one hour, which York words as too many flame recycles.
- The flame sensor
- A thin rod in the flame tells the control the burner is lit. Soot or a film on the rod makes it read poorly, and the control thinks the flame is gone. Cleaning it is a short job for a technician.
- Gas pressure and the valve
- Low supply pressure or a valve that does not hold open can starve the flame. Both need gauges and are not owner work.
- Why wait
- Because the control retries after one hour, the furnace may run again and then lock out, which can look like a random fault. Note the times.
- Outdoor checks
- Look for snow, ice or a nest at the intake and exhaust terminations.
- Safety
- Never block or modify the vent.
- What a flame sensor looks like
- The sensor is a short metal rod, bent or straight, held in the burner area by one screw and a wire. It sits in the flame. Over time, a film of residue builds on the rod and the control cannot read the flame. A technician cleans it with fine abrasive and checks it again, which often fixes the problem for a season or two.
- Gas supply questions
- Low pressure can come from the regulator, a partly closed valve, an undersized pipe or an issue with the supply from the utility. A technician measures the pressure with a manometer, with the furnace off and then running. If other gas appliances in the home also act oddly, tell the gas utility.
- What not to do
- Do not remove the burner box, scrape the sensor yourself or tape over the control. Do not keep resetting the furnace at the thermostat to defeat the lockout, because each retry sends gas into a burner that may not light well.
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 8 red flashes mean on a York YP9C modulating gas furnace?+
Lockout due to too many flame recycles. The code occurs if flame is lost five times during a single heating cycle. The control locks out for 1 hour and then tries again.
How long is the lockout?+
York says one hour, then it tries again.
What are the likely causes?+
A dirty flame sensor, low gas pressure or a faulty valve.
Can I clean the sensor?+
A technician should.