Middleby Marshall Pizza Oven Alert Rear Belt Jammed: Belt Stopped

What does Middleby Marshall Rear Belt Jammed mean?

Many conveyor ovens carry the product on two belts, and the controller of a PS640G or PS670G watches both. Rear Belt Jammed means the rear belt has stopped, even though the other belt may still be turning. That is why it can go unnoticed: the front of the oven looks normal until product backs up at the exit end. Pizzas that stop inside the chamber keep baking, so they can burn. The likely cause is something caught at the rear belt or at the exit, such as a pan, a screen or a food item that fell off. If nothing is in the way, the next suspects are belt tension and wear on the drive chain, the rear belt drive motor, or the speed sensing that reports the rear belt. The operator can clear what is plainly in the way, but only after the chamber and belts have cooled, since both are hot. If the alert returns after clearing, or if nothing was blocking the belt, a technician should look at the rear drive.

Affected models and control systems

This applies to Middleby Marshall PS640 and PS670 conveyor ovens with the touch-screen controller, such as the PS640G and PS670G. Other controller generations use different belt alerts.

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

• Rear Belt Jammed on the touch screen
• Product backing up at the exit end
• Rear belt still while the front belt turns
• Items stuck at the oven exit

Possible causes

Listed in Middleby Marshall's documentation

• Obstructions at the rear belt or exit end
• Belt tension and drive chain wear
• The rear belt drive motor
• Speed sensing for the rear belt

Other likely causes — what usually sits behind Rear Belt Jammed on this control. A technician confirms which one it is before any part is replaced.

• A pan wedged between the exit ramp and the belt
• Drive chain stretched so it skips under load
• Speed sensor misreading the rear belt as stopped

Safe checks before calling for service

How a technician diagnoses Rear Belt Jammed

1. Read the alert and inspect the rear belt and exit area.
2. Check belt tension and the drive chain.
3. Check supply to the rear drive motor and measure current.
4. Test the rear belt speed sensing.
5. Compare the rear drive with the front.
6. Replace the drive part only after the test.

How Rear Belt Jammed differs from similar codes

Front Belt Jammed is the same alert for the other belt; the rear belt problem is easier to miss.

Technical reference

Document

PS640G I&O Manual 60251 Rev J, screen alerts

Edition

P/N 60251 rev J, (c) 2023 Middleby Marshall Inc.

Models / control

Middleby Marshall PS640 / PS670 touch-screen controller (screen alert)

Section

Section 3 Operation - Quick Reference: Troubleshooting, Screen Alerts table, printed p. 28

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.