The Case Of The Not So Hot Midmark Autoclave


We got a call from Jeremy this morning about his M11 autoclave not working.

He told us he started by selecting the “pouch” cycle.  It filled with water and then advanced to the heat up stage like it is supposed to…but it never got hot…not even warm…in fact, there was no heat at all!

Just the facts:

  • Jeremy’s unit is an older Midmark M11 Autoclave with the Red LED Display
  • It successfully completed the ‘Fill Cycle” and advanced to the “Heat Up” Stage
  • The Temperature started at 74 ° F (room temperature) and never changed…even after hours of leaving it on
  • It never generated an error code

While the lack of heat and no “error code” was the biggest clue as to what the source of the problem was, it is always good practice to rule out other possibilities

First Things First

  • Test The Over-Heat Thermostat to see if it is faulty (the Over-Heat Thermostat is a safety device:  it cuts the power to the heating element if it thinks it is too hot, to protect the system) (Click Here for Directions) (
  • Test the resistance on the heating element (an easy test requiring a cheap ohm meter) Click Here and scroll down the page for directions (
  • Test the heating element for a direct short (also an easy test using the same ohm meter)
  • Clean The Temperature Probe
  • Test The Temperature Probe (Unplug the Temperature Probe from the board, then run another cycle to see if the problem goes away)
  • Make Sure the PC Board is Grounded.  Remove the ground screw, clean the floor area and both sides of the bracket where the ground screw passes thru (and the screw itself) to remove any corrosion, dirt and debris.  Make sure the ground screw is fastened tightly to the cabinet

Jeremy completed all of the tests successfully, and no problems were found.

Based on the lack of heat and no error code, this confirmed our original suspicion, that the issue was with the PC Board

There is a relay on the board that is known as the K1 relay. This relay controls the heat..turning it on an off in response to the signals it gets from the Temperature Probe

The K1 relay is the black box located above the area where the leads from the heating element plug in.  In most cases, when the relay goes out, there is a burn mark on the back of the board where the relay is attached.  If there is a burn mark, then the board is not repairable and will need to be replaced

In Jeremy’s case, there was not a burn mark.  Even so, from following all of the steps above, it left only one conclusion.  The relay is defective, and the board will need to be replaced

Replacing the board remedied the problem for Jeremy, and the Midmark M11 Autoclave is now working like new again

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