It's possible the overpressure plug is cracked and needs to be replaced. All-American recommends replacement every 12 months and it's a good idea to keep a spare on hand.

You might find this All-American troubleshooting guide handy. It does discuss your problem on page 3.

Carol

Here is a link that might be useful: All-American Troubleshooting Guide

In addition to cracking as Carol said, they can dry and shrink during storage. Sometimes just running the canner for a bit but nothing but water in it will allow the plug to re-expand. Worth a try. And i agree that have spare parts on hand is always a good idea.

Another personal experience - if you have hard water as I do - is lime build-up in the exhaust vent. You may not be able to see it but it is there and is just enough to reduce flow. Adding some vinegar to the water and allowing active steaming through the vent for 20 mins. can help soften it and then a stiff pipe cleaner will clean it out.

Dave

Thanks for the advice - I'll try running the canner and adding some vinegar to the water.