This article explains the possible causes and solutions to a Midmark M9-M11 New Style autoclave Error Code C647.

Midmark M9/M11 Error Code C647 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 C646. 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.




Gauge pressure inside chamber is equal to or greater than 2.18 psi (15 kPa) during DRY mode, or 0.7 psi (5 kPa) during DOOR mode.

Causes, Checks and Actions

If Door did not open before DRY mode… 

Possible Cause 1: Door spring missing/damaged. 
  • Check 1: If the door motor releases the latch, but the door remains closed, Inspect door spring for damage.
  • Check 2: Verify if door is at the vented position. (Push in on door with out lifting handle)
  • Check 3: Verify the QTY of door springs. (M11- QTY 2, M9-QTY 1)
  • Action: Replace door springs.

Possible Cause 2: Chamber filter clogged.
  • Check: Check if chamber filter is clogged.
  • Action: Clean / Replace filter. (Clean with Speed-Clean and brush)

M9 Mesh Vent Filter OEM available here

M11 Mesh Vent Filter OEM available here

Possible Cause 3: Door/dam gaskets. 
  • Check A: Inspect door / dam gaskets for proper installation and any signs of sticking.
  • Action A: Install door / dam gaskets properly.


  • Check B: If new gasket, check if wire ring in gasket is preventing gasket from fully being seated.
  • Action B: Temporarily remove wire ring. Re-install wire ring after gasket is fully seated.
Possible Cause 5: Door pins/latch binding. 
  • Check A: With door open, door handle should move Up / Down freely.
  • Action A: Clean door pins / latch mechanism. (Clean with Synthetic Dry Protectant – Aerosol / Spray on)


  • Check B: Inspect latch mechanism for wear / damage.
  • Action B: Replace worn / damaged components.

Possible Cause 6: Door motor system/latch “hanging up”.
  • Check A: Remove the door cover, and RH side panel. With the door closed, run the ‘Door Open Test’. Watch for any mechanical issues that may prevent the door from opening. Refer to: Service Diagnostics (I/O Test)
  • Action A: Replace worn / damaged components.


  • Check B: Verify Door Motor is angled as close to PC board as possible.
  • Action B: Adjust door motor angle.


  • Check C: Place in Service Diagnostics Mode. With the door closed, run the Door Open Test. Watch for any mechanical issues that may prevent full rotation of door motor cam. Refer to: Service Diagnostics
  • Action C: Replace door motor.

Midmark Door Motor available here. 

  • Check D: Check if the connecting rod is installed in the proper location on the door motor cam. (9 for M9, 11 for M11)
  • Action D: Install connecting rod in the proper 9 or 11 location on the door motor cam.

If Door did open before DRY mode….

Possible Cause 7: PC Board malfunctioning.
  • Check 1: Perform: Heating Element Supply Voltage Test (With harness attached to leads should have line voltage in test mode)
  • Check 2: Perform: Main PC Board Relay Test (Check TP1 & TP2 for an acceptable range: 10 to 14 VDC)
  • Check 3: Perform: Main PC Board Pressure Transducer Voltage Test (Acceptable range: 4.0 to 6.0 VDC)
  • Action: Replace Main PC board.

M9 PC Board OEM available here

M11 PC Board OEM available here

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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