common autoclave problems

7 Common Autoclave Problems You Should be Aware Of

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Written by: Scott Mechler

BS Mechanical Engineering, Mechanical Engineer

In an ideal world, laboratory autoclaves would always work exactly as intended. Unfortunately, issues can and do arise — the key to resolving them is knowing what to look for.

In this article, we’ll outline seven of the most common autoclave problems and how to identify them.

1. The sterilizer won’t reach the temperature set-point.

Autoclave users have the ability to customize sterilization cycles based on a number of parameters, including sterilization temperature. If the autoclave fails to reach the designated temperature in the time it takes to run the sterilization cycle, it will either abort the cycle or sound an alarm (i.e. low temperature alarm.)

There are a few reasons why an autoclave might not be able to reach the sterilization temperature within the given period of time. For example, perhaps the power source for the steam generator isn’t turned on. Certain autoclave models use integral steam generators, which sit below the autoclave chamber. This type of steam generator is typically hooked up to its own high-voltage power source, which can be turned off when the rest of the unit is still on. If the user doesn’t realize that the power source for the generator is turned off, while the rest of the sterilizer appears to be powered on, this would prevent the sterilizer from reaching the designated temperature.

Other reasons why the autoclave might not reach sterilization temperature include:

  • The steam generator is need of repair.
  • There is a clog in the chamber drain (i.e. check the chamber drain strainer) that is preventing air from escaping the chamber and the steam from reaching the correct pressure and temperature.
  • The temperature the user has entered exceeds the autoclave’s maximum temperature allowance.

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2. The load is damaged by the autoclave.

There are a few ways that an autoclave can damage a load.

The first is melting. Autoclaves run at very high temperatures — temperatures that can melt certain materials, such as some plastics. Therefore, it’s important to ensure that any items loaded into a sterilizer are autoclave-safe. Fortunately, most laboratory equipment will either say whether it’s autoclave-safe or list its melting point. A melted load can damage a sterilizer, so it’s especially important to train autoclave users to be careful about what they load into the machine.

Another common issue is liquid loss, either in the form of evaporation or boil-over. The boiling temperature of water increases as pressure increases. For example, in order for steam to reach 121° C (250° F), autoclave pressure must increase to 14-16 PSI. If a  cylinder or flask full of water is loaded into an autoclave and run at a temperature of 121° C, as soon as the cycle is completed the pressure is released, and water will start to boil over. This could cause splashing, which is a safety hazard; a smaller container could even explode. For laboratories that produce broth, evaporation or boil-over is money down the drain.

The best way to avoid this problem is to run a specialized Liquids Cycle that releases the chamber pressure slowly instead of all at once. This gives the liquids time to cool down, so it isn’t at its boiling point when the pressure is released.  All Consolidated autoclaves are equipped with a Liquids Cycle.

Burned sugars are another common way for loads to be damaged by an autoclave. Much like liquids have a boiling point, sugars have a caramelization point. The best way to avoid this issue is to simultaneously increase the length of a sterilization cycle and decrease the temperature. For laboratories that handle extremely sensitive goods, Consolidated Sterilizer Systems offers a Low Temperature Cycle.

3. Goods are not sterilized.

Improperly sterilized goods can lead to contamination, growth in the media, or a failed Biological Indicator.  The reasons a sterilizer may not sterilize the load are many:  improper loading (e.g. covering the drain port, overpacking), steam dryness, component failure, insufficient steam, wrong cycle type, user error, etc.  The best way to ensure proper sterilization is to validate the unit using a biological indicator (BI). In order to validate an autoclave, simply place the BI into a typical load. When the load is complete, take out the packet and put it in a special broth and incubate to see if there’s any growth. If there is no growth, it’s safe to assume that your load is validated to that cycle recipe and sterilization should occur.  Please note: This paragraph is a very short over-simplification of the processes around validation and cycle development.

4. The load is wet after the sterilization cycle has ended — even with drying time.

This typically happens when autoclave users load porous goods such as cloth and paper close together, which causes them to act like a sponge and retain water. The easiest way to avoid this issue is to adopt a loading style that spaces out goods, such as a rack or cart-and-carriage arrangement. Another option is to invest in an autoclave with a vacuum capability, which dries goods at the end of the cycle. The sterilizer simply pulls the vacuum inside the chamber and evaporates any remaining water. You can read more about wet packs here.

5. A large liquid load causes the sterilization cycle to abort.

Large liquid loads take an exceptionally long time to heat, which can cause sterilization cycles to abort. Therefore, the best way to sterilize liquids is to space them out in as many small containers as possible. Another way to prevent this common autoclave problem is to use an F0 cycle, which enables the autoclave to count the time that it spends heating up the water toward the total sterilization time.

6. There’s no steam in the jacket.

Similar to the first item on this list, the easiest way to prevent this issue is to ensure that the power source for the steam generator is turned on. It’s also important to make sure that the steam line feeds into the autoclave correctly and to check the heating elements to see whether they’re damaged or broken.

7. Excessive amounts of water are going down the drain.  No water is going down the drain, just steam.

Almost every autoclave has some sort of waste water cooling valve that opens and closes automatically in order to cool down the steam that’s coming out of the sterilizer before going down the drain. Both of the common autoclave problems mentioned above are caused by this valve being broken in some way.

Most autoclaves have an extra cold water line just before the drain with a temperature sensor. When that sensor detects steam, it adds a little water to it to cool down that steam. If that temperature sensor is broken or the valve is broken, it can cause the water to either dump out, which will make the autoclave sound like a sink all the time, or it could cause the steam to go down the drain if the valve is stuck closed.

Excessive water going down the drain is a clear indication that the valve is broken in the “open” position.  Steam coming out of the drain is a sign that the valve is broken in the “closed” position, and that there’s no cooling water coming out of it.

To learn more about autoclaves, check out our video here:


If you’re experiencing these or other common autoclave problems, contact Consolidated Sterilizer Systems today. Our team of specialists have the expertise to resolve any issues you may be facing and get your autoclave back in working order.

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