PRV on water heater

Check out this picture. This water heater has a temperature limiting device that shuts of power to the element so the valve at the top would only need to be a pressure relief valve and a discharge pipe. Obviously there is no discharge pipe but possibly the round part at the top could be a knob for a PRV. I have never seen one like this before. My first thought was that the valve was missing altogether but there was pressure on the system so something is keeping the pressure in. Any of you recognize this?


Never seen anything like it. Appears to be plugged. No matter what, its not right and needs repaired/replacement as deemed necessary by a licensed plumber. What is in the background is that mold on wall?

Yes, it definitely needs work. Not a huge issue because it is a rental but I was curious about this type of valve.
That is not mould on the wall. It is a stone foundation. What you are seeing is the different colour stones and the mortar.

LOL…just looked weird in the picture.

It’s not plugged.

The hex on top is the pressure relief adjustment.

This is a very old pressure only relief valve.

Michael is correct.
I used to see a lot of those adjustable relief valves years ago. It probably wouldn’t work if needed now.