8 Common Autoclave Problems You Should Know

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.

Key Takeaways:

• Most autoclave problems are the result of user error or component wear.
• The most important thing you can do to catch problems early is to run routine biological indicator tests and log the results.
• Many common autoclave problems share a root cause and can be resolved without a service call if they’re identified quickly.
• When problems persist after basic troubleshooting, contact your manufacturer before attempting repairs, especially for electrical or pressure system issues.

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 in 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.
• The door gasket is worn or damaged, preventing the chamber from holding pressure long enough to reach the set point.
• A temperature sensor or thermocouple is malfunctioning and providing inaccurate readings.

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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 runs 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 (BI). There are many reasons why an autoclave may not sterilize the load.

These include:

• Improper loading, such as covering the drain port or overpacking
• Steam dryness
• Component failure
• Insufficient steam
• User error

One often overlooked cause of sterilization failure is incorrect cycle selection. A gravity cycle, for example, will not reliably sterilize wrapped instruments or porous loads because it relies on steam displacing air downward, a process that cannot fully penetrate wrapped or dense materials. Porous loads and wrapped instruments require a pre-vacuum or dynamic air removal cycle to ensure complete steam penetration. Always match the cycle type to the load type, not just the time and temperature parameters.

Other than selecting the appropriate cycle type, the best way to ensure proper sterilization is to validate the unit with a BI. At a very high level, this entails placing a BI into a typical load. When the load is complete, remove the packet, place it into a specialized broth, and incubate it to see if there’s any growth. If there is no growth present, it’s safe to assume that your load is validated to that cycle type and that proper sterilization should occur.

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. These pockets of water are known as wet packs.

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.

If wet loads persist despite proper loading and adequate drying time, the problem may be mechanical rather than procedural. An issue with the bellows — the component that allows excess moisture to return to the clean water reservoir during the cycle — can cause moisture to remain trapped in the autoclave chamber. A worn or a leaking door gasket can also prevent the vacuum phase from drawing down effectively, leaving residual moisture in the load. In either case, contact your service provider to inspect and replace the affected component.

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. 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 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, OR no water is going down the drain, just steam.

Almost every autoclave has some sort of wastewater cooling valve that opens and closes automatically 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 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.

8. The door gasket is leaking steam.

The door gasket is the seal that maintains airtight pressure in an autoclave chamber. A damaged or malfunctioning gasket prevents an autoclave from building or holding the pressure required for sterilization. There may be issues with your door gasket if you see visible steam escaping from the door during the cycle, you hear a hissing sound, the autoclave fails to reach the pressure set point, or you receive an error code indicating insufficient pressure.

Gaskets degrade over time through repeated thermal cycling, compression, and exposure to cleaning agents. Inspecting the door gasket should be part of routine maintenance — look for flattening, cracking, accumulation of debris, or any visible deformation. Replacing a gasket is a fairly simple repair and can be completed in-house. Just be sure to use a manufacturer-specified replacement part, as an off-specification gasket can fail to seal properly.

To reduce gasket wear, clean the gasket and door channel regularly to remove residue. For pre-vacuum autoclaves, a periodic vacuum leak test can help you catch gasket degradation early on, before it results in a failed sterilization cycle or an unexpected service call.

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

 

When to Call a Service Technician

You can identify and resolve many of the autoclave problems described above at the facility level with basic troubleshooting. However, some issues require a qualified service technician and should not be attempted in house:

• Electrical faults: Any suspected issue with heating elements, thermocouples, or the autoclave’s primary control system should be diagnosed by a certified technician, as incorrect repairs to electrical or high-voltage components can damage the unit and create safety hazards.
• Persistent pressure failures: If the autoclave continues to fail to reach or hold pressure after gasket replacement and valve inspection, you should have a technician evaluate the full pressure system.
• Repeated failed BI tests: A failed BI that you can’t attribute to a loading error or incorrect cycle selection could be a sign of a deeper sterilization process failure. Do not return the autoclave to service until a professional has diagnosed and resolved the issue.

When in doubt, contact a trusted service technician before attempting a repair.

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.

Frequently Asked Questions

Q: What are common autoclave problems?

A: The most common autoclave problems are:

• Sterilizer failing to reach temperature set point
• Load damaged by autoclave
• Goods not properly sterilized
• Wet loads after sterilization is complete
• Large liquid loads causing cycle to abort
• No steam in the jacket
• Excessive amounts of water going down the drain
• No water going down the drain, only steam
• Door gasket leaking steam

Most of these issues fall into one of two categories: user error or component wear.

Q: What is the lifespan of an autoclave machine?

A: The lifespan of an autoclave typically ranges from 10 to 20 years, depending on the quality of the unit, how heavily it’s used, and how consistently it’s maintained. Autoclaves that receive regular preventative maintenance typically reach — or even exceed — the higher end of that range. If your autoclave requires constant repairs or is no longer able to reliably reach cycle parameters, it may be approaching end of life.

Q: What should I do if my autoclave fails to work properly?

A: If your autoclave fails to work properly, start by checking the basics: confirm that all power sources are on, that the door is fully closed, and the gasket is intact. You should also check the error code displayed on the control panel against your manual. If the issue is a wet load or aborted cycle, check your loading configuration and cycle selection before assuming it’s a mechanical issue. If basic troubleshooting doesn’t resolve the problem, contact your service provider for assistance.

Q: What is the most common reason for sterilization failure?

A: The most common reasons for sterilization failure are improper loading or selecting the wrong cycle type for the load. When the autoclave chamber is packed too tightly, steam cannot fully penetrate the load, leaving some areas inadequately sterilized. Running the wrong cycle also prevents full steam penetration, regardless of whether the autoclave meets the designated time and temperature parameters.

Q: What is one thing you should never do when loading an autoclave?

A: One thing you should never do when loading an autoclave is to cover or obstruct the chamber drain strainer. The drain strainer catches debris and prevents it from clogging the drain line. A covered or clogged strainer slows or blocks the exhaust line entirely, which can prevent you from safely opening the chamber. It can also disrupt the flow of steam bleed, creating a discrepancy between the autoclave’s indicated temperature and its actual temperature, causing loads to be inadequately sterilized. It’s important to take a few minutes after each cycle to clean the chamber drain strainer.