Honeywell Home Security F21 Fix: Zone 21 Fault Quick Guide
F21 on a Honeywell home alarm usually means a fault on zone 21. Here’s the fast way to find the bad sensor, clear the fault, and know when it’s time to replace parts or the whole system.
F21 on a Honeywell home alarm usually means a fault on zone 21. Here’s the fast way to find the bad sensor, clear the fault, and know when it’s time to replace parts or the whole system.