Why does a pressure canner need testing?
Low-acid foods such as vegetables, meats, poultry and broth must be heated to a level that water bath canning cannot reach, and a pressure canner makes that possible. The canner reports its pressure through a gauge. If the gauge is wrong, the food may not reach the conditions that destroy the bacteria that cause botulism, and you cannot see or smell the difference.
That is why every tested recipe assumes a canner that reads correctly, and why checking one is part of safe canning, not an optional extra.
Treat testing like checking a thermometer before you rely on it. Many households have inherited a canner from a relative, and it may have been used for decades without a check. That does not mean it is unsafe, but it does mean it deserves a test. An older canner may also be missing parts, or the manual may have been lost, so a call to the manufacturer is a good first step.
What is the difference between dial and weighted gauges?
A dial gauge has a needle that moves across a numbered face. Over time the spring inside can lose accuracy, and a knock or drop can damage it. A weighted gauge uses a weight that rocks or jiggles over a vent to show pressure, and it has no dial to drift out of calibration, though it still needs to be kept clean and used as the manual directs.
Each type has its own instructions. Read the manual for your exact model, since the way you judge pressure differs between them.
- Dial gauges need periodic accuracy checks
- Weighted gauges need clean vents and correct weights
- Follow the manual for your exact canner
- Never mix parts between brands or models
Where can you get a dial gauge tested?
Many county extension offices test dial gauges, sometimes for free or a small fee, and some run testing days. Some canner makers also test their own gauges or sell replacements. Call your extension office early in the season and ask how it works, whether you need to bring the lid or just the gauge, and how long it takes.
Do not try to test a gauge with improvised tools. The test needs proper equipment and a reference gauge. Bring the whole lid if the tester asks for it, or just the gauge if that is all they need. Ask whether the tester can also check the vent pipe and safety valve. Bring your canner's make and model, since that helps identify parts.
How often should a gauge be checked?
Ask your extension office or the maker for their current recommendation. Many sources suggest checking before each canning season and any time the gauge has been dropped or you suspect a problem. If you use the canner heavily, checks may need to be more frequent.
Keep a note of the date and result of each test with your canning records.
What do the results mean?
The tester will tell you whether the gauge reads accurately or by how much it is off. Your extension agent can explain what the result means for your recipes and whether you can keep using the gauge. If the gauge is off by more than the allowed amount, replace it with the part the maker specifies.
Do not guess at an adjustment on your own. Ask the tester how to handle it for the recipes you plan to use.
What else should you check on the canner?
Besides the gauge, check that the vent pipe is clear, the sealing ring or gasket is in good condition, the safety valve works and the lid locks and seals as it should. Look at the body for dents and warping, and check that the rack is present.
Replace worn parts with the exact parts from the maker. Do not use substitutes. Write the test date and result on a tag or in your records, and attach a note to the canner so the next user knows when it was last checked. If you lend your canner to others, share the manual and the test result with them.
What if the canner fails the test or you are unsure?
Do not use the canner for low-acid foods until it has been repaired or replaced. Ask your extension office or the manufacturer what to do. If you have home-canned food made in a canner you now doubt, ask your extension office what to do with it. Do not taste it to decide.
Keep canning with tested recipes and a verified canner, and stay with the National Center for Home Food Preservation for current guidance.
Key takeaways
- A wrong gauge can leave low-acid food unsafe without any visible sign.
- Dial gauges need periodic accuracy testing, often available through extension offices.
- Check the vent, gasket, valve and lid along with the gauge.
- Do not use a canner you doubt; ask extension or the maker.
Sources and further reading
Last reviewed: November 12, 2026. Written by the Homestead & Small Farm Editorial Team. See our editorial policy.