Zone 5 probably needs repair--ususally the diaphragm is the culprit. If you change the diaphragm and the valve still does not function properly, the whole valve will need to be changed.

You will need to turn your main water back on to figure out valve locations. Then follow your owners manual for your timer pertaining to MANUAL operation. Ideally manual station operation, where you can run one station at a time. Then walk to your valve boxes and see which valve is operating.

I agree with irrigirl. Its probably a rock or something in the valve for zone 5 not letting the diaphragm seal. Go through each valve and turn them on manually by twisting the solenoid counter clockwise until you find the valve that runs zone 5. Take out the screws on top of the valve. open it up (make sure to take note of where everything goes) and visually inspect the diaphragm and inside the valve for rocks and debris. Turn the water on to flush the valve. Put the valve back together. See if that works.

irrigirl shared some great advice. I think he will definitely help you. It's really sad when something breaks .. I had a problem with the water supply when I moved to a new apartment. The pipes were constantly leaking in the bathroom. I called the plumber more than three times, but about a month after his visit, I started having these problems again. I really didn't know what to do in this situation. I was looking for a solution to this problem in various forums and I was advised to independently choose high-quality materials to replace the leaking zone. I found a high quality globe valve and asked a plumber to replace it. I was surprised that for over a year I hadn't encountered this problem again. Perhaps if you also use better components, then you will be able to avoid a lot of problems.

https://www.halolawn.com/how-to-fix-a-sprinkler-system/