Honeywell Home Security F35 Error Code Guide (Fast Fix)

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What This Error Means

On Honeywell home security panels, F35 usually means one thing: Fault on Zone 35.

Zone 35 is just a sensor slot in the system, so whatever device is programmed as zone 35 is being reported as open, triggered, or in trouble, and the panel will not arm until that zone is normal or bypassed.

Check the keypad text next to the fault; it will say something like FAULT 35 BACK DOOR or FAULT 35 HALL MOTION so you know which physical sensor is yelling.

Official Fix

Here is the by-the-book way to clear F35 on a Honeywell security panel.

  • Look at the keypad display and note exactly what it says for zone 35. Example: FAULT 35 KITCHEN WINDOW. That text tells you which sensor to inspect.
  • Go to that door, window, or motion detector:
    • Doors and windows: make sure they are fully closed and not warped. The magnet and sensor body should be within a few millimeters of each other when closed.
    • Motion detector: make sure nothing is moving in its view (pets, fans, curtains) and the cover is fully snapped on.
  • If it is a wireless sensor:
    • Check the cover. If it is loose or not seated, the tamper switch will hold the zone in fault.
    • Replace the battery if it is old. Most Honeywell wireless contacts use coin cells or small lithium batteries. Match type and polarity exactly.
    • Put the cover back on firmly until it clicks.
  • If it is a wired sensor:
    • Gently wiggle the sensor and magnet. If the fault comes and goes, the reed switch or wiring may be failing.
    • At the panel, verify the wires for zone 35 are tight in the terminals and not corroded or broken.
  • Go back to the keypad and try:
    • Enter your user code, then OFF (usually the 1 key) twice to clear the fault display.
    • The READY light should come on. If it does, arm and disarm once to be sure the fault stays gone.
  • If FAULT 35 is still there after you have confirmed the door or window is definitely closed, the official recommendation is to call your alarm provider or a Honeywell dealer to test the zone and replace the sensor if needed.

The Technician’s Trick

Here is how a field tech gets you running when F35 just will not clear and you need the system armed now.

  • First, check what zone 35 really is. If the label says SMOKE, FIRE, or CO, stop. Do not bypass a life safety zone; call a pro. If it says a door, window, or motion, continue.
  • Quick bypass to make the system ready. On most Honeywell keypads: enter your 4 digit code, press 6 (bypass), then 35, then arm as usual. The keypad should show BYPASS 35 and the READY light will come on. Remember: that sensor is now unprotected until you remove the bypass.
  • Magnet test for door and window contacts. Grab a small fridge magnet, hold it tight against the sensor body, and watch the keypad:
    • If the fault clears when the magnet is on the sensor, the door or window is not bringing the factory magnet close enough. Reposition the magnet or add a slightly stronger replacement.
    • If the fault does not clear even with the magnet, the sensor or its wiring is bad.
  • Hard reset of a flaky wireless contact. Pop the cover, pull the battery for 30 seconds, reinstall it, then close the cover firmly. Walk back to the keypad and disarm twice. Many random F35 issues vanish after a clean power cycle on the sensor.
  • Last resort before calling for service. If zone 35 is a rarely used window, leave it bypassed and schedule a sensor replacement when it is convenient instead of paying for an emergency visit.

Is It Worth Fixing? (The Financial Verdict)

  • ✅ Fix: Single sensor on an otherwise solid Honeywell system, panel is under 10–12 years old, and the issue tracks to one obvious bad contact or dead battery.
  • ⚠️ Debatable: Multiple zones keep faulting like F35, the system uses very old wireless sensors, or you are already paying for an expensive monitoring contract and the panel is near end of life.
  • ❌ Replace: Panel is 15 plus years old, not supported by your alarm company, cellular communicator is obsolete, or a tech quotes you for several sensors plus a service call that adds up close to the cost of a modern, app based security system.

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See also

Dealing with other devices throwing strange error codes? These guides break them down the same way.