Practice Tips #27: Troubleshooting Sterilizers (Part 1)

This month, rather than dedicating an entire issue to a specific make or model of sterilizer (such as we did with Decoding the Statim) we’re going to discuss general theories of operation and steps to take to troubleshoot steam or chemical vapor sterilizers. These concepts can be applied to most any brand or model of sterilizer.

First of all, many common problems associated with sterilizers crop up due to maintenance and upkeep issues. We have covered general sterilizer maintenance in a past edition, Sterilizer Maintenance, and we strongly recommend reviewing it and printing it for your staff before moving forward. The first step should always be proper maintenance. Nonetheless, even with proper maintenance, errors can occur. Many state and local agencies recommend weekly spore testing of sterilizers, in part due to the many things that can go wrong.

A number of the tests you will need to perform will require a multimeter (see our issue on multimeters for basics on using this helpful tool). Most components can be tested with the sterilizer unplugged. It is best to have any electronic component unplugged when servicing if possible. Regardless, always exercise caution when checking electronic components and equipment.

Two of the most commonly observed problems with sterilizers are failure to achieve pressure or improper temperature (either too low or too high). This month, we’ll focus on pressure, next month we’ll cover temperature.


Low pressure is normally the only pressure-related concern encountered (persistent high pressure is rare and obvious as the safety valve will crack releasing pressure). Low pressure can be attributed to one of three basic causes:

  1. Inadequate heat to create steam
  2. Poor or no water flow into the chamber from the reservoir (usually due to a clog somewhere but could simply be due to lack of water in the reservoir)
  3. Pressure leak

The first step in resolving pressure issues is to narrow down which of these three primary categories is causing the problem.


What does the unit thermometer/temperature gauge read? If it is at or above 135° C (275° F) you do not likely have a heating problem. Have you verified this temperature is achieved using a lag thermometer? In this case, move on to the next possibility, water. (If your unit fails to heat or does not achieve adequate heat, you’ll need to wait for next months Part 2 – Temperature Issues.)

Poor or no water flow

Almost all sterilizers incorporate some sort of water filter. Usually, there is a filter in the chamber at the point water flows into it. Check this filter for signs of wear or clogging. Changing this filter should be part of your annual maintenance routine. Nonetheless, filters can wear prematurely. There is often a filter in the reservoir as well. A simple visual inspection of the filters should be adequate to determine their condition. If they don’t look clean, they aren’t and should be replaced. These filters are normally sintered bronze or stainless steel so they should have the appropriate metallic color.

Fill-line filter shown inside a Validator chamber

While in the reservoir checking your filter (or to see if there is one – not all sterilzers will incorporate this filter), check the water level. Make certain that the reservoir is properly filled.

Speaking of water – this might also be a good time to verify that nothing but distilled or de-ionized water is being used in your autoclave. Using tap water or similar untreated water will certainly lead to much more common clogs and other potential issues (such as staining of instruments).

If your filters check out, examine the reservoir itself and the water line that feeds from the reservoir to the chamber. These lines can also become clogged over time. Using a small cleaning brush or similar device may be one of the most effective ways of checking the water line.

Usually the water flows through some sort of valve (e.g. solenoid), checking this valve for clogs or function can be more involved and the steps to check it will vary depending on the specific make and model of your sterilizer. Call our tech support staff to speak about the particulars of your sterilizer to diagnose valves.

Pressure Leak

  1. Observation – watch the sterilizer as it pressurizes. Often, you can see steam escaping from a particular location. This can be a good indicator of where the leakage is occurring. For example, if you can see steam leaking around the door, replace the door gasket. It may be necessary (and certainly will be helpful) to run a cycle with the cover removed from your sterilizer so that you can better see where any leak is originating.
  2. Door Gasket. Check for signs of wear, cracks, chips, etc. The door gasket should also be replaced every year as part of routine maintenance. If it’s been more than a year, replace your gasket.
  3. Safety valve – sterilizers have a safety valve to prevent over-pressurization. This valve can get stuck open and leak. There will be a metal ring on the end of the safety valve. Using a needle-nose pliers, pull the ring to see if it moves. It should move with some effort and return. If it does not move or does not spring back when released, the safety valve has failed and should be replaced. Usually the safety valve is inside the reservoir or at the back or your sterilizer. Shown below is the Validator Pressure Relief Valve:


    Safety valve inside of a Validator

  4. (Air) Bellows – most sterilizers will incorporate some sort of bellows as well. This is also often something that needs to be replaced annually, but this can vary depending on make and model of sterilizer. Sometimes a visual inspection of the bellows can give you a good idea of its condition.
  5. Electronic component failure – many sterilizers (particularly automatic sterilizers) will incorporate steam sensors and various types of electronic controls that will control pressure. A failure of one of these components can impede proper pressurization. Call our tech support staff for particulars of testing electronic components of your sterilizer. To check most of these components you will need a multi-meter.

Note: The things we suggest checking are presented in the order in which they should be checked (most likely to least likely as well as simplest to most involved to check).

Watch next month for Part 2: Sterilizer Troubleshooting – Temperature Issues.