Honeywell Vista No AC Power — How to Fix

What Does This Error Mean?

Honeywell Vista No AC (displayed as 'NO AC' or 'SYSTEM LO PWR' on 6160 series keypads) means the panel has lost its 16.5VAC transformer input and is running on battery backup. The alarm system continues to operate normally from the battery. Restore AC power by checking the transformer outlet and the breaker feeding it — the trouble clears automatically once power is restored.

Affected Models

Honeywell Vista 20P
Honeywell Vista 15P
Honeywell Vista 21iP
Honeywell Vista 48LA
Honeywell LYNX Plus

Common Causes

The circuit breaker feeding the transformer's outlet has tripped
The transformer plug has been accidentally unplugged from the wall outlet
A general power outage has interrupted mains power to the property
The panel's 16.5VAC step-down transformer has failed internally

How to Fix It

Check whether a general power outage has occurred

If lights and appliances in the area are also off, the outage is a utility issue. The Honeywell Vista will run from battery backup for 4–12 hours depending on your battery size. Wait for utility power to be restored — the trouble clears automatically.
Locate the transformer and verify it is plugged in and the outlet is live

The Honeywell 1321 or 1361 transformer is a plug-in box connected to a 120V outlet near the panel enclosure. Ensure it is firmly seated. Test the outlet with a lamp or phone charger to confirm it has power.
Check the circuit breaker feeding the transformer outlet

Look for a tripped breaker in the main panel (a breaker in the middle or OFF position). Reset it. If it immediately trips again, the outlet circuit has a wiring fault that needs an electrician's attention.
Test transformer secondary output voltage

With a multimeter on AC voltage, measure across the two transformer secondary output wires going into the panel's AC terminals. Expected output is approximately 16.5–18VAC. No output with a live outlet confirms transformer failure — replace with an equivalent Honeywell transformer.
Clear the trouble notification on the keypad after restoring AC

Once AC is restored, press * and enter your master code or installer code to silence and acknowledge the trouble. The 'NO AC' indicator should clear within a minute as the panel recognises its power input is back.

Frequently Asked Questions

How long will my Honeywell Vista system run on battery with no AC?

A standard 12V 4Ah battery provides roughly 4–6 hours of standby. A 7Ah battery extends this to 8–12 hours. Battery capacity degrades over time — batteries older than 3–5 years may not hold their rated capacity. Replace the battery every 3–5 years for reliable backup.

Will my monitoring company be notified of the AC power failure?

Most monitoring configurations include AC loss reporting with a time delay — typically 30 minutes to 4 hours — to avoid nuisance calls during brief outages. Extended AC loss will be reported to your monitoring centre. Confirm with your alarm company what delay is programmed for your account.