York YP9C five red flashes: flame where the control did not ask for it
York YP9C five red flashes reports flame detected outside the commanded sequence. This is a stop condition, and the page explains why no reset applies.
What this means
Five red flashes on a York YP9C control reports flame present at a time the control did not command it. That is a statement about the gas train rather than about ignition performance, so the furnace should be taken out of use and handed to a licensed engineer rather than reset and observed.
Equipment and model context
York YP9C modulating condensing gas furnaces documented in the York installation manual
- YP9C060
- YP9C080
- YP9C100
- YP9C120
The flash table referenced here is the one published for the York YP9C modulating condensing furnace. York assigns flash counts differently across its furnace lines, and equipment from related brands on similar control platforms carries its own table, so the model on the rating plate governs.
What you may notice
- The control shows five red flashes while the thermostat is satisfied and no heating has been requested.
- The circulating blower runs at a time when the furnace should be idle.
- Warmth continues to come from the supply registers after the heating cycle should have ended.
Likely causes
- A gas valve that fails to seat fully lets gas reach the burner after the control has commanded it closed.
- Flame persisting past the end of a commanded cycle can be detected during the period the control expects the burner out.
- The sensing circuit can also be wrong in the direction that raises a false alarm, reporting a signal with nothing alight.
Diagnostic paths
Warm air keeps arriving after the cycle ends
Supply registers continue to deliver warmth well past the point where the thermostat has been satisfied and the cycle should have finished.
Turn the furnace off at its dedicated service switch and stop using it. Continued heat output with no call is the symptom this code exists to report.
The code shows on an apparently idle furnace
Five flashes repeat, but there is no warmth, no burner sound, and no smell from the furnace at any point.
Take the furnace out of use anyway and arrange service. A sensing circuit that reports flame incorrectly cannot be trusted to report a real one.
Any smell of gas is present
An odour resembling gas is noticeable anywhere in the property, whether or not the furnace appears to be operating.
Leave the building, avoid operating switches, and call the emergency number your gas supplier publishes from outside. Everything else on this page waits.
Ordinary flame proving asks whether a commanded flame arrived. This check asks the opposite question during the idle period, and an affirmative answer there is a gas train issue rather than an ignition one.
- Thermostat satisfiedThe furnace should be resting
- Gas train closedNothing should be reaching the burner
- Signal presentThe sensor still sees a flame
- Furnace withdrawnThe control ends operation entirely
| Element | What the code implies | Established by |
|---|---|---|
| Gas valve seating | It may not be closing fully | Engineer testing the valve |
| Burner shutdown | Flame may persist past command | Observed sequence timing |
| Sensing circuit | It may report flame falsely | Measured flame signal |
| Ignition performance | Nothing at all | A different code covers that |
A code that changes who is allowed to act
On most furnace faults the homeowner has a genuine role: check the filter, look at the vent terminal, record the pattern, then hand over. This one removes almost all of that. Two of the three candidate causes sit inside the gas train, and the third means the safety circuit cannot be relied on. None of them is improved by observation from the room, and all of them are made worse by another heating cycle.
So the page ends where the code begins. Establish whether there is a gas smell, isolate the appliance, and call somebody licensed. That is not caution for its own sake: it reflects that uncommanded combustion is one of the few things a furnace control is designed to treat as unconditional.
Why a false reading still takes the furnace out of use
It is tempting to hope for the third cause, a sensing circuit reporting a flame that does not exist, because it sounds like the cheap outcome. Even if that turns out to be the case, the furnace still stops. The flame sensing circuit is the mechanism by which the control decides whether it is safe to keep the gas valve open, and a circuit that reports flame incorrectly in one direction cannot be assumed reliable in the other.
That is the logic behind treating all three branches identically until measurement separates them. The flame sensing explainer covers how the proving circuit works and what a measured signal looks like, and the Goodman equivalent of this fault shows how another manufacturer words the same condition.
What to give the technician
Give the engineer the York model and serial number, the five red flash count, whether warmth or burner activity continued after the cycle, and whether any gas odour was noticed.
Safe homeowner checks
- Check for any smell of gas first, and if one is present leave the property and call the gas emergency number from outside before anything else.
- Isolate the appliance using the service switch fitted beside it, which ends the cycling without touching anything inside the cabinet.
- Write down whether continued warmth or burner activity was observed, and at what point in the cycle the flashes appear.
When to call a technician
- Gas valve testing, burner inspection, and flame sensing circuit measurement on a modulating condensing furnace are licensed gas engineering tasks.
- Do not restore the furnace to service to see whether the code returns. A repeat cycle is the risk this code is warning about.
Questions people ask about this
Can I keep using my York furnace with this code?
No. The condition reported is flame present when the control did not command it, which concerns the gas train. The appliance should be isolated and handed to a licensed engineer.
Why does the blower run when the furnace is idle?
Moving air across the exchanger is how the control sheds heat it did not intend to produce. The blower running during an idle period is that protective response, and it is not evidence that the thermostat has called.
Could the flame sensor alone be at fault?
It is one of the possibilities, and it still stops the furnace. A sensing circuit that misreports in one direction cannot be assumed accurate in the other, so the appliance is taken out of use until it is measured.
Evidence recordHow this page was checked
service manual, official manufacturer support article · checked 2026-09-15
Every technical claim above was written from primary documentation held in the HVAC Bench evidence record: York technical literature. Where a source limits a definition to certain models, test conditions, or product classes, that limit is repeated here rather than generalised.
- Documentation class
- service manual, official manufacturer support article
- Scope of the definition
- York YP9C modulating condensing gas furnaces documented in the York installation manual
- Last checked
- 2026-09-15