This article explains the possible causes and solutions to a Midmark M9-M11 New Style autoclave Error Code C533.

Midmark M9/M11 Error Code C533 Leave a comment

In this article, we’re going to explain one of the many error codes that can affect your Midmark M9/Midmark M11 autoclave. This article will focus specifically on error code C533. We’ll tell you about the problem, what displays when the error occurs, its possible causes, and the course of action to take to resolve said error.


However if you’re more of a visual learner we have a video on this error code available here. 





Sterilization mode not reached after 25 minutes. 

Causes, Checks and Actions

 Possible Cause 1: Maintenance not performed. 

Check: Verify weekly & monthly maintenance has been performed by customer. Refer to User Guide.

Action: Perform monthly maintenance. 

 Possible Cause 2: Sterilizer is unlevel. (remove tray / trays)  

Check 1: Verify support surface is level.

Check 2: Verify water on all sides of chamber are equal.

Action: Place sterilizer on a level support surface.

Possible Cause 3: Heating Element malfunction.
  • Check: Inspect heating element. Heating element should lay flat in the bottom of the chamber. Heating element should be free of any flaking / pitting. Perform: Heating Element Resistance Test (should read 9-11 Ω)
  • Action: Replace heating element.

M9 Heating Element OEM available here

M11 Heating Element OEM available here

Possible Cause 4: Temperature sensor malfunctioning. 
  • Check A: Check for residue build up on temperature sensor probe.
  • Action A: Clean sensor probe with Speed-Clean, distilled water, and abrasive pad.

Speed Clean available here.


  • Check B: Check that nothing is touching or crowding the temperature sensor. (Example: trays, pouches, cassettes, etc.)
  • Action B: Reposition items so nothing touches or crowds the temperature sensor.


  • Check C: Perform: Temperature Sensor Resistance Test. Allow sensor to cool to room temperature before testing. Acceptable range 1.07-1.1K Ω. Refer to: Temperature Sensor Resistance Test
  • Action C: Replace Temperature Sensor

M9 Temperature Sensor available here

M11 Temperature Sensor available here. 


  • Check D: Perform: Temperature Sensor Supply Voltage Test. Disconnect sensor harness from J12 on PC board. On pins 1 & 2 acceptable range is 4.0 – 6.0 VDC. Refer to: Temperature Sensor Supply Voltage Test
  • Action D: Replace Main PC Board.

M9 PC Board OEM available here

M11 PC Board OEM available here

Possible Cause 5: Pressure Leaks
  • Check: Check for loose / worn door and dam gaskets or water leaking around door. Verify door and dam gaskets are installed properly. (Replace gasket kit 1x year)
  • Action: Clean / Replace gaskets.

M9 Door Gaskets OEM available here

M11 Door Gaskets OEM available here

  • Check: Replacement fill / vent valve solenoid requires rectifier harness for DC coil.
  • Action: Install rectifier harness.


  • Check: Check for voltage flow through rectifier harness. Refer to: Fill / Vent Valve Supply Voltage Test
  • Action: Replace rectifier harness.


  • Check: Leaking or defective vent valve. (Check for water leaking from condensing coil spout) Perform: Vent Valve Test
  • Action: Clean / Replace vent valve.

M9 Vent Valve Repair Kit OEM available here

M11 Vent Valve Repair Kit OEM available here

  • Check: Leaking or defective fill valve. Check for water leaking back into reservoir thru the fill line. (Look for bubbles coming from bottom of reservoir) Perform: Fill Valve Test
  • Action: Clean / Replace fill valve.

M9 Fill Valve OEM available here

M11 Fill Valve OEM available here

  • Check: Leaking or defective air valve. Check for excessive steam coming thru condensing coil spout. NOTE: During the HEAT & VENT modes, it is normal for steam to be exhausted thru the spout.
  • Action: Clean / Replace air valve.

M9 Air Valve OEM available here

M11 Air Valve OEM available here

  • Check: Leaking or defective Pressure Relief Valve. Check for water / steam leakage from beneath the rear of the sterilizer. Perform: Pressure Relief Valve Test
  • Action: Replace pressure relief valve.

M9 Safety Valve OEM available here

M11 Safety Valve OEM available here

  • Check: Pressure transducer tubing leaking. Check for steam leakage at pressure transducer tubing connections.
  • Action: Secure pressure transducer tubing connections with high temperature cable ties.

M9 Pressure Tubing OEM available here

M11 Pressure Tubing OEM available here

  • Check: Check all plumbing fitting connections for leakage.
  • Action: Tighten or replace fittings.

As always if you have any questions about this process or anything else please feel free to contact us and take advantage of our “FREE TECH SUPPORT.”

We also offer FREE VIRTUAL TECH SUPPORT to “See and Talk” with a “Real Time Live Technician” for any problems you may be in need of help with.

You can also use our “FREE MAINTENANCE PROGRAM”. Take the guesswork and worrying about what unit is due for maintenance and which maintenance cycle it is time for. We will keep track of all your autoclaves and let you know when it’s time for anything.

The Midmark M9 autoclave is available here. 

We also have the Midmark M11 autoclave here. 

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