Middleby Marshall Pizza Oven Error Code ALM 1: High Limit
ALM 1 on a Middleby Marshall PS520 or PS528 conveyor oven is the high-limit indication. It shows when the oven reaches 650 F (343 C), and the burner is shut down automatically. Follow the Daily Shutdown procedure, wait until the chamber is completely cool, and call us.
High: the oven reached its safety limit and the burner is shut down.
- Code
- ALM 1
- Maker
- Middleby Marshall
- Equipment
- Pizza ovens
- Applies to
- PS520 / PS528 digital temperature controller
What does Middleby Marshall error code ALM 1 mean?
Conveyor ovens such as the PS528G, PS528E and PS520G carry a digital temperature controller. As well as holding the setpoint, the controller has a high-limit alarm. ALM 1 shows when the oven reaches 650 F (343 C), and at that point the burner is shut down automatically. Heating stops so that the oven and the product are protected. The alarm is a safety response, not a nuisance trip. It can come from several places: a controller or setting that did not cut off at setpoint, a thermocouple reading lower than the real chamber temperature so the oven kept heating, blower airflow that no longer spreads heat evenly, or heat controls that failed to cut off. Restarting the oven over and over does not help and can stress the parts. The manual's step is the Daily Shutdown procedure, then waiting until the chamber is completely cool. Only after the cause is found should the oven be run again. A technician can compare the thermocouple with a known thermometer and test the controls.
Affected models and control systems
This applies to Middleby Marshall PS520 and PS528 conveyor ovens with the digital temperature controller, such as the PS528G, PS528E and PS520G. Other controller generations use different alarm numbers.
Code numbers and their meaning can change between control generations. We match the full model and control before acting on a code.
What you may notice
- ALM 1 on the temperature display
- Burner shutting down on its own
- Oven too hot to touch around the chamber
- Pizzas browning too fast before the alarm
Possible causes
Listed in Middleby Marshall's documentation
- The temperature controller and its high-limit setting
- The thermocouple reading against a known thermometer
- Blower airflow that spreads heat in the chamber
- The heat controls that failed to cut off at setpoint
Other likely causes — what usually sits behind error code ALM 1 on this control. A technician confirms which one it is before any part is replaced.
- Thermocouple that has drifted and under-reads the chamber
- Gas valve that is slow to close after the setpoint is reached
- Blower filter or fan clogged with flour dust, leaving hot spots near the sensor
Safe checks before calling for service
- Follow the Daily Shutdown procedure in the owner's manual.
- Wait until the chamber is completely cool.
- Do not restart it over and over.
- Note the setpoint you were using and how long the oven had been on.
- Call us to find the cause. Smell gas? Get out of the building and phone the utility.
How a technician diagnoses error code ALM 1
- Read the alarm and the setpoint the controller held.
- Compare the thermocouple with a known reference thermometer in the chamber.
- Check the controller's high-limit setting.
- Check blower operation and airflow.
- Test the heat controls, including the gas valve, for proper cutoff.
- Replace the part only after the test.
- Testing the gas valve and burner controls involves a live gas train, which only a licensed technician should open.
- A high-temperature oven can hold heat long after shutdown and can burn.
- Comparing the thermocouple needs a reference thermometer in the chamber and the controller's own settings.
How error code ALM 1 differs from similar codes
ALM 1 is the 650 F high limit, unlike the other alarm numbers on this controller, which report other conditions.
Technical reference
- Document
- PS528G I&O Manual 63935-C, ALM 1
- Edition
- Part No. 63935 Rev. C (c) 2012 Middleby Marshall Inc.
- Models / control
- PS520 / PS528 digital temperature controller
- Section
- Section 3 Operation, Blower Switch / temperature controller paragraph, printed p. 20 (PDF p. 24); no alarm code table
- Checked
- October 2026
We use the maker's document to read the code and do not reproduce it. Always confirm the complete model and control before applying these steps.
Related Middleby Marshall pizza oven error codes
Can I reset ALM 1 and keep baking?
Not safely. Let the oven cool and find the cause before it runs again.
Will it clear itself?
It can once the oven cools, but the cause remains.
Is ALM 1 a gas problem?
It can involve the gas valve cutting off late, but the thermocouple and controller are checked first.
Need help with Middleby Marshall error code ALM 1?
A technician confirms the cause on site and gives you the price in writing before any work starts.