KeepRite Error Code 3: Pressure switch did not close or reopened (Furnace)

Updated October 13, 2026 · by Aurora Star Tech Inc.

KeepRite error code 3 on a furnace means: Pressure switch did not close or reopened. It is also called KeepRite diagnostic code 3.

High severityFurnaceKeepRite (F/G)9MXE Single-Stage Furnace · KeepRite (F/G)9MXT Two-Stage Furnace

Homeowner? What KeepRite code 3 means for you

Call a technician Your furnace is reporting: Pressure switch did not close or reopened. The furnace has locked out or cannot run properly. One reset is fine; if the code comes back, it needs a licensed technician to find the cause.

Safe things you can check yourself

Check the thermostat: right mode (Heat or Cool), set a few degrees past room temperature, and fresh batteries if it uses them.
Make sure the unit has power: its on/off switch (often looks like a light switch near the unit) is ON and the breaker in the electrical panel is not tripped.
Make sure the furnace front door or panel is closed properly; many furnaces will not run with the door switch open.
Look at the air filter. If it is grey and clogged, replace it; a blocked filter causes many shutdowns.
Outside, make sure the intake and exhaust pipes or vent cap are not blocked by snow, ice, leaves or a nest.
Check that the gas valve next to the furnace is open (handle in line with the pipe). Do not force it.
Try one reset: turn the power off for 30 seconds, then back on. If the code comes back, stop resetting and call a technician.

Call (647) 657-2977 Book a service call

Licensed technicians serving Vaughan, Toronto and the GTA.

What does KeepRite error code 3 mean?

9MXE: the collector-box (LPS) or inducer-housing (HPS) switch did not prove or opened again. 9MXT: the low-heat switch did not prove or opened again. If it opens during the blower-on delay the blower runs through its off delay. If open over 5 minutes the inducer stops for 15 minutes and retries. 9MXE: if the HPS stays open 1 minute, the furnace locks out for 3 hours after repeated tries.

Applies to: KeepRite (F/G)9MXE single-stage and (F/G)9MXT two-stage 95% furnaces

Common causes of KeepRite code 3

Vent pipe undersized or restricted, or water lying in a sagging vent
Plugged condensate drain
Air leak between the vestibule and blower compartment

A technician checks these and 5 other possible causes on site before replacing any part.

Safety: Gas, electrical and refrigerant work must be done by a licensed technician. Turn off power and gas before servicing, never bypass a safety control, and always follow the manufacturer's manual for your exact model.

KeepRite models that use code 3

G9MXE0401410A G9MXE0401714A G9MXE0601412A G9MXE0601714A G9MXE0801716A G9MXE0802120A G9MXE1002120A G9MXE1202422A G9MXT0401410A G9MXT0401712A G9MXT0601412A G9MXT0601714A G9MXT0801716A G9MXT0802120A G9MXT1002120A G9MXT1202422A

Other KeepRite Furnace codes

Code	Meaning
1+2	Blower running after power-up (normal)
2	Pressure switch stuck closed (did not open)
4	Limit or rollout circuit open
5	Flame sensed with gas valve off
6	Flame not proved during ignition trial
6+1	Ignition lockout after 4 failed tries
7	Limit circuit lockout
8	Gas heating lockout - manual reset needed
9	High-heat pressure switch or relay did not close or reopened
10	Line voltage polarity reversed
LED off	Status LED dark - no power to the control or blown 3 A fuse
LED steady ON	Status LED on solid - control lockout (resets after 1 hour)

All KeepRite Furnace error codes →

KeepRite code 3: homeowner questions

What does KeepRite code 3 mean?

Pressure switch did not close or reopened. 9MXE: the collector-box (LPS) or inducer-housing (HPS) switch did not prove or opened again. 9MXT: the low-heat switch did not prove or opened again. If it opens during the blower-on delay the blower runs through its off delay. If open…

Is it safe to keep using my furnace with code 3?

It depends on the cause. The furnace has locked out or cannot run properly. One reset is fine; if the code comes back, it needs a licensed technician to find the cause.

Can I reset KeepRite code 3 myself?

You can try one reset (power off for 30 seconds, then on). If KeepRite code 3 comes back, the cause is still there and a licensed technician should check it.

Who can fix KeepRite code 3 near me?

Aurora Star Tech Inc. repairs KeepRite furnaces in Vaughan, Toronto and across the GTA. Call (647) 657-2977 or book a service call online.

Homeowner help: Furnace Not Turning On: What to Check · Furnace Blinking Light: What the Flash Codes Mean

Troubleshooting guides

Blowing cold air All brands · Furnace
No heat All brands · Furnace
Short cycling All brands · Furnace
No heat, control ignores the thermostat - KeepRite (F/G)9MXE KeepRite · Furnace
No heat, control ignores the thermostat - KeepRite (F/G)9MXT KeepRite · Furnace
Reading stored codes and component test - KeepRite (F/G)9MXE KeepRite · Furnace
Reading stored codes and component test - KeepRite (F/G)9MXT KeepRite · Furnace

Source: KeepRite/ICP (F/G)9MXE Service and Technical Support Manual 440 04 4311 09, Fig. 16 troubleshooting flow chart, p.24-25; KeepRite/ICP (F/G)9MXT Service and Technical Support Manual 440 04 4321 10, Fig. 16, p.24-25. Written in our own words as a summary; always check the original manual.

General guidance for qualified technicians. The manufacturer's installation and service manual and local codes always take priority. Aurora Star Tech is not affiliated with, endorsed by or sponsored by any equipment manufacturer; brand and model names are used only to identify equipment and belong to their owners.