HVAC Code Lookup

Ruud Furnace Code 46

Soft lockout

Low pressure switch open with the inducer running on low speed. Same switch as code 45, but it dropped out after the furnace stepped down to low-fire heat. The furnace post-purges and retries ignition if the heat call is still there.

Manual wording: “LOW PRESSURE SWITCH OPEN, INDUCER ON LOW SPEED ... This fault indicates that the low pressure switch is open when the inducer is energized at low speed.”

Documented for: (-)97V, (-)96V two-stage and modulating furnaces

Likely causes, most common first

  1. Blockage or improper termination in either the inlet or exhaust vents
  2. The flue vent length and/or number of elbows exceeds the maximum number specified
  3. Faulty or disconnected inducer
  4. Faulty control board (inducer relay)
  5. High altitude kit not installed in areas of high elevation
  6. Loose or faulty wiring
  7. Disconnected, blocked, split or cut pressure switch hoses
  8. Wind gusts (sporadic)
  9. Faulty pressure switch

What you can safely check yourself

  • Check the outdoor intake and exhaust terminations for snow, ice or debris.
  • Check the condensate drain and trap for a clog.
  • Power cycle once at the furnace switch after clearing any blockage.

When to call a technician

Vent length, high-altitude kits, inducer and pressure switch work are all technician jobs. Never bypass the pressure switch.

A Ruud furnace throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.

Sources

Other Ruud codes