York · Furnace

Rapid red flash Twinning error or wrong 24 V phasing

Medium severity York UTEC IFC furnacesYork White-Rodgers IFC furnaces

What the control is telling you

Continuous fast red flashing: the 24 V phasing is reversed between twinned furnaces, or a twinning connection problem exists.

Applies to: York/JCI residential gas furnaces: York UTEC IFC furnaces, York White-Rodgers IFC furnaces

Likely causes

Transformer leads swapped on one of two twinned furnaces
Twinning wire fault
ECM / X13 furnaces wrongly twinned (not allowed)

Test and repair steps

Check the transformer secondary leads match on both twinned furnaces.
Check the twinning terminal wire between boards.
Do not twin furnaces with X13 or variable speed ECM blowers - these boards cannot be twinned.
Refer to York service tip ST-031-08 on twinning.
To read stored codes with no thermostat call active, tap the LAST ERROR button briefly (under 5 s); up to five codes play back newest first. Two green flashes = memory empty. Hold the button 5 s or more to clear (three green flashes confirm).

Settings for these units

Clearance to combustibles · York TM9V
Filter size by return location · York TM9V

Other codes on the same units

8 red flashes Flame lost repeatedly (recycles)
9 red flashes Polarity reversed or bad ground
10 red flashes Gas valve powered with no heat call
11 red flashes Limit open 5-15 minutes - blower failure
12 red flashes Hot surface igniter open / igniter failure
LED steady off Board LED dark - no power to control
Rapid amber flash Weak flame signal
Steady on (any color) LED lit solid - internal control fault

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Source: York All JCI single-two-stage furnaces with UTEC IFC board codes ST-045-09.pdf - section Fault Code LED Flashes; York JCI single-two-stage furnaces with White-Rodgers-Emerson IFC (older installed base) codes ST-028-07.pdf - section Fault Code Sheets. Summarized in our own words; check the original manual for your model.

Homeowner looking at this code? See what it means for you and when to call a technician.

For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.