Middleby Marshall Oven Alert: Main or Combustion Blower Problem
A Main Blower problem or Combustion Blower problem alert on a Middleby Marshall PS640 or PS670 means the computer detected a problem with the main blower or the burner blower. Cut power, let the oven cool, and do not keep baking with the alert on the screen. Tell us which blower the alert named when you call.
High: a blower failure affects heating and combustion, and the burner may shut down.
- Code
- Main Blower problem / Combustion Blower problem
- Maker
- Middleby Marshall
- Equipment
- Pizza ovens
- Applies to
- Middleby Marshall PS640 / PS670 touch-screen controller (screen alert)
What does Middleby Marshall Main Blower problem / Combustion Blower problem mean?
Two blowers matter in a conveyor oven. The main blower moves hot air through the chamber and over the product. The combustion blower feeds air to the burner. The controller on a PS640G or PS670G checks both, and when it detects a problem with either it shows Main Blower problem or Combustion Blower problem. With the main blower down, the oven can bake unevenly because the heat is no longer moving. With the combustion blower down, the burner may not get the air it needs and the control shuts it off. Either way, the owner's manual says a qualified service technician should correct it. The possible reasons are the blower motor and wheel, the motor wiring and connectors, the blower sensing and the controller, or restrictions in the air path around the blower. Flour and grease can coat a blower wheel and throw it out of balance. Since a combustion problem can also involve the gas train, a gas smell means leaving the building and calling the gas utility from outside.
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 blower 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
- Main Blower problem or Combustion Blower problem on the touch screen
- Uneven baking from front to back
- Burner shutting down
- Unusual noise or no airflow from the blower area
Possible causes
Listed in Middleby Marshall's documentation
- The blower motor and wheel
- Motor wiring and connectors
- Blower sensing and the controller
- Airflow restrictions around the blower
Other likely causes — what usually sits behind Main Blower problem / Combustion Blower problem on this control. A technician confirms which one it is before any part is replaced.
- Wheel coated in grease and flour dust and out of balance
- Motor bearings worn, so it runs hot and trips
- Combustion air intake partly blocked by dust
Safe checks before calling for service
- Cut power to the oven and let it cool off.
- Do not keep baking with the alert on the screen.
- Note whether the alert named the Main Blower or the Combustion Blower.
- Call us. If you ever smell gas, go outside and call the gas utility from there.
How a technician diagnoses Main Blower problem / Combustion Blower problem
- Read the alert and note which blower it names.
- Check the blower wheel for buildup and free rotation.
- Measure motor supply and current with a meter.
- Check wiring, connectors and the blower sensing.
- Check air paths and the combustion air intake.
- Replace the motor or sensing only after the test.
- Blower motors run on live wiring and sit next to a gas-fired burner.
- Combustion air problems can affect the burner, which only a licensed technician should adjust.
- The owner's manual says a qualified service technician should correct this alert.
How Main Blower problem / Combustion Blower problem differs from similar codes
The two blower alerts share one cause list; High Temp Error is a separate alert about the sensor or PLC.
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.
Related Middleby Marshall pizza oven error codes
Can I keep baking if only the Main Blower is named?
Not safely. Heat will be uneven, and the manual wants a technician to correct it.
Does the Combustion Blower alert mean a gas leak?
Not by itself, but a gas smell means leaving the building and calling the utility.
Will a restart clear it?
Possibly once, but the cause stays until it is tested.
Need help with Middleby Marshall Main Blower problem / Combustion Blower problem?
A technician confirms the cause on site and gives you the price in writing before any work starts.