HTP · Boiler

FOU Outdoor sensor fault

Low severity Elite EL

What the control is telling you

Outdoor sensor is shorted, open, or the outdoor temperature is below -40 F. Boiler keeps running and ignores outdoor reset, using the programmed boiler temperature.

Applies to: EL-80, EL-110, EL-150, EL-220, EL-299, EL-399 (N/LP)

Likely causes

Outdoor sensor wiring damaged or shorted
Sensor defective

Test and repair steps

Inspect the outdoor sensor wiring for damage or shorts and repair
Measure the sensor resistance and compare with the chart; replace if out of range

Models that show this code

12 models in Elite EL

EL-110 LPEL-110 NEL-150 LPEL-150 NEL-220 LPEL-220 NEL-299 LPEL-299 NEL-399 LPEL-399 NEL-80 LPEL-80 N

Other codes on the same units

CASCADE NO SENSOR Cascade - no system sensor
DHW Temperature blocking - DHW demand
FL Low water flow
FLU High flue pressure
GAS VALVE ON / RUN Ignition then run status
LOCKOUT Lockout (display message)
LOU 24 volt supply low
MAINTENANCE REQUIRED Service reminder

Save it for the next call

Star this code in the HVACopedia app and keep the whole library on your phone for jobs with no signal.

Open the app

Source: Elite EL-80 N Installation Manual (LP-293), p. 67. 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.