York YP9C two red flashes: the draft proving circuit did not behave
York YP9C two red flashes concerns the pressure switch circuit and the inducer that is meant to close it. Learn which observations narrow it fastest.
What this means
Two red flashes on a York YP9C control points at the draft proving circuit: the pressure switch has not reached the state the control expects for the stage of the sequence it is in. The count identifies the circuit, not the component, so the inducer, the vent path, the condensate arrangement, and the switch itself are all inside the reading.
Equipment and model context
York YP9C modulating condensing gas furnaces documented in the York installation manual
- YP9C060
- YP9C080
- YP9C100
- YP9C120
This applies to the York YP9C modulating condensing furnace as documented in its installation manual. York uses different flash tables on other furnace lines, and a modulating furnace proves draft across more than one firing rate, which changes what a fault at a particular stage implies compared with a single-stage appliance.
What you may notice
- The inducer runs through its cycle and then everything stops, with no ignition attempt at any point.
- Heat is produced at one firing rate and the furnace faults when it tries to change rate.
- The fault appears far more readily in wet or freezing weather than in mild conditions.
Likely causes
- Anything narrowing the terminal outdoors, from a wasp nest to a drift of snow banked against the wall, moves the pressure the switch is asked to prove.
- Liquid sitting where a pressure signal should travel turns the tube into a column of water, and the switch then reports that column instead of the draft.
- An inducer that is not producing the airflow it should, whether from a wheel deposit or a motor condition, leaves the switch unable to close.
Diagnostic paths
It fails only when the furnace changes firing rate
Heat is delivered steadily for a period, and the fault appears at the moment the furnace steps up or down rather than at the start of a cycle.
Record which direction the change was going. A modulating furnace proves draft at more than one rate, and a fault confined to one transition is a precise clue.
Nothing ever lights, every time
Each call for heat produces inducer noise and then silence, with no ignition attempt occurring on any cycle.
Keep the appliance switched off and inspect the outdoor terminals from ground level only. Ladders, poles, and hands inside a terminal are all outside what this check covers.
The pattern follows the weather
The furnace runs normally in mild conditions and faults during hard frost, heavy rain, or strong wind.
Keep a note of the outdoor temperature and wind direction each time. Weather-linked faults direct attention to the terminations and to condensate freezing.
A modulating furnace does not prove draft once. It proves it at each firing rate it uses, which means a fault can hide at one rate and appear at another, and where it appears is diagnostic information in itself.
- Low fireDraft proven at the lowest rate
- Rate changeThe proving condition shifts
- High fireDraft proven again at full rate
- Fault locationWhich rate fails narrows the cause
| Location | How it shows | Season it favours |
|---|---|---|
| Vent or intake terminal | Fails from the start of a cycle | Winter and storm conditions |
| Condensate trap or tubing | Intermittent, sometimes clears | Cold spells with high humidity |
| Inducer performance | Consistent across conditions | Any time of year |
| Switch or wiring | Consistent, unaffected by weather | Any time of year |
What a condensing furnace adds to the problem
A condensing furnace extracts enough heat from the flue gas that water falls out of it, and that water has to be collected and drained. The result is a furnace with small-bore tubing carrying both pressure signals and liquid, sometimes in close proximity. When condensate ends up where a pressure signal should be, the switch stops reporting draft and starts reporting a column of water.
That is why draft proving faults on high-efficiency equipment behave seasonally in a way that older furnaces did not. The fault can arrive with a cold snap, disappear in a thaw, and return with the next one, which makes it maddening to report and straightforward to explain once the pattern is written down.
Reading the count honestly
A flash count on a furnace control is a compression of a much larger diagnostic tree into a single number, and York's own installation manual is the document that expands it. Reading two red flashes as a failed pressure switch is the mistake this page exists to head off, because the switch is the reporting device rather than the usual subject of the report.
The useful posture is to treat the count as naming a circuit and then let observation choose the branch. Whether ignition was ever attempted, whether the fault follows firing rate, and whether it follows the weather each eliminate a large part of the tree at no cost. The furnace pressure switch reference explains the proving sequence, and the frozen condensate guide covers the winter case in detail.
What to give the technician
Supply the York model and serial number, the two red flash count, whether ignition was attempted, which firing rate the fault follows, and the weather conditions when it occurred.
Safe homeowner checks
- Count the flashes carefully through the sight glass, keeping the blower door closed so control power is not interrupted.
- Check the outdoor vent and intake terminations from ground level for snow, ice, nests, or plant growth without climbing or probing.
- Note whether ignition is ever attempted and whether the fault is linked to a change in firing rate.
Is a reset appropriate?
Removing power clears the display and the control repeats the same proving checks on the next call. A fault that tracks the weather can appear to be cleared by a reset when the conditions have simply changed.
When to call a technician
- Measuring draft pressure, testing the inducer, clearing condensate traps, and verifying switch operation at each firing rate are licensed gas-furnace tasks.
- Any indoor smell of combustion products, or a carbon monoxide alarm, means leaving the appliance off, getting fresh air into the space, and calling the gas emergency number before anything else.
Questions people ask about this
Does two red flashes mean my York pressure switch has failed?
The count names the proving circuit rather than the switch. Vent obstruction, condensate in the tubing, and inducer performance can all leave the switch unable to reach the expected state with the switch itself in good order.
Why does my York furnace only fault in cold weather?
Condensing furnaces produce liquid that can freeze in terminations and tubing, and a snow-covered or iced terminal changes the pressure being proven. That makes the fault seasonal without any part changing.
Is a modulating furnace harder to diagnose here?
It proves draft at more than one firing rate, so a fault can be present at one rate and absent at another. That adds steps for the engineer and gives the owner a more precise observation to report.
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