Learn how to clean or replace the vacuum relief valve in Bezzera BZ13 PM and Bezzera BZ13 DE espresso machines. Symptoms indicating need for service include continuous discharge of steam from your return tube into the reservoir. Be aware it's normal to hear some hissing and have some moisture discharge as the machine is heating up to full temp. If discharge continues when boiler temp is above 212F/100C the vacuum relief valve likely needs service.
Bezzera BZ13: How to Clean or Replace the Vacuum Relief Valve