HVAC Code Lookup

Ruud Furnace Code 45

Soft lockout

Low pressure switch open with the inducer running on high speed. The switch has to close once the inducer starts before ignition is allowed. The inducer keeps trying in five-minute cycles until the switch closes or the heat call ends.

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

Documented for: (-)97V, (-)96V

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. Loose or faulty wiring
  6. Disconnected, blocked, split or cut pressure switch hoses
  7. Wind gusts (sporadic)
  8. Faulty pressure switch

What you can safely check yourself

  • Go outside and check the intake and exhaust pipe terminations for snow, ice, leaves, insect screens or a nest.
  • On a high-efficiency furnace, check the condensate drain and trap for a clog - a full trap can block the vent.
  • Power cycle once at the furnace switch after clearing any blockage.

When to call a technician

If the terminations are clear and the code returns, the inducer, pressure switch, hoses or vent run needs a technician. Never jumper 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