The coolroom alarm went off overnight: five checks that tell you what broke

Last reviewed: 18 July 2026

If you want the full response process — acknowledging the alarm, reading the temperature trend remotely, deciding whether to drive in at all — that's covered in what to do when the alarm goes off after hours. This page picks up at the door.

Before anything: measure, don't read

Do not trust the display on the control panel. Displays fail, sensors drift, and a controller that has lost its probe will happily show you a number that means nothing. Put an independent thermometer inside — a probe thermometer through the door seal, or a cheap min-max unit you keep on a shelf for exactly this night. Product temperature beats air temperature: air recovers in minutes when a door closes, but the middle of a stacked crate tells you what actually happened over the last few hours.

While you're at it, keep the door shut as much as you can. A full coolroom is a large cold mass and it loses temperature slowly with the door closed. Every minute the door stands open while you poke around costs you part of the buffer you'll want later. Get in, place the thermometer, get out, and do the rest of the checks from outside.

Check 1: the door

The most common cause of an overnight alarm is the least dramatic one. A door left ajar after the last delivery, a strip curtain caught in the latch, a wedge someone forgot, a seal that has torn or hardened and no longer closes the gap. Run your hand around the seal and feel for cold air escaping. Look at the bottom corner — seals fail there first.

If the door is the problem, close it properly and watch the temperature. A healthy coolroom that was only warm because of the door will start pulling down straight away. If it does, your night is nearly over: note the time, note the highest reading, and skip to the stock decision below.

Check 2: ice on the evaporator

Open the door briefly and look at the evaporator unit — the finned coil with fans, usually mounted high inside. If it's cased in ice or frost, airflow is blocked, and the room warms even though the refrigeration plant is running flat out. An iced coil usually means a failed defrost cycle, a heater element gone, or a door problem earlier in the week that loaded the coil with moisture.

Ice is a fridgie job. Do not attack it with anything sharp; fins bend and coils puncture. What you can usefully do is tell the tech "the evaporator is iced solid" on the phone, because they'll bring the right gear and expect a defrost fault rather than a mystery.

Check 3: is the compressor running

Stand near the plant — outside unit or motor room — and listen. Three states, three stories:

• Running, and the room is holding or recovering. The system may simply be losing the fight against a door or an iced coil. Go back to checks 1 and 2.
• Running, but the room keeps warming. Likely a refrigerant or valve problem. The plant sounds normal and does nothing. Fridgie, tonight.
• Silent. Either it's off on a safety cut-out, or it has no power. That's check 4.

Note which state you found. "The compressor is running but it's not cooling" and "the compressor is dead silent" send a tech down two different diagnostic paths, and saying the right sentence can shave an hour off the visit.

Check 4: power

Find the switchboard. Look for a tripped breaker or RCD on the coolroom circuit, and check the isolator near the plant hasn't been knocked off. If a breaker has tripped, you can reset it once. If it trips again, stop — something is genuinely faulty and repeatedly resetting it risks turning an electrical fault into a fire. Leave it off and tell the tech.

A power fault is also the one case where the coolroom itself may be innocent. If half the premises is dark too, your problem is supply, not refrigeration.

What to tell the fridgie

One short brief: actual measured temperature and the time you measured it, door status, ice or no ice on the evaporator, compressor state, power state. Five facts. A tech who hears all five before leaving home arrives with the right parts and the right expectations.

The stock call, briefly

Chilled food that spends too long above safe temperature has to be assessed, and past a certain point, binned. The rules run on time-out-of-temperature, which is exactly why you noted the time at every step. Keep the door shut, don't move stock into an unknown fridge in a rush, and work through the framework in the after-hours page. The exact thresholds for your business come from your food safety program and your council — confirm them there, not from a web page.

Write down what you found

Log the event: date, time the alarm fired, what you found, what fixed it. One alarm is a bad night. A second alarm with the same cause is a pattern — a door habit, a defrost cycle failing at the same hour, a seal on the way out. Patterns are cheap to fix once you can see them, and the log is what makes them visible. If you don't yet have monitoring that records this for you, that's the case for an alarm that logs.

The short version

Measure the real temperature with your own thermometer and keep the door shut — the cold mass inside is buying you time. Then work the order: door and seal, ice on the evaporator, compressor running or silent, power at the board. Phone the fridgie with those five facts and the timeline. Log the event, because the second alarm with the same cause is a maintenance problem wearing an emergency costume.

General guidance only — food safety thresholds and electrical work are matters for your food safety program, your council, and licensed trades.