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Recently we had an extended water outage. When water came back, pressure in the lines was much higher. The hot water heater started leaking from the pressure release valve and after flipping it a few times, it didn't stop, so I was prepared to go replace it, but then I accidentally pushed on the end of the pull bar that goes to the valve and the flow stopped.
Tried flipping it again, it leaked again, pushed the bar and it stopped.
Am I right in thinking the spring is shot, time to replace it?
I would replace the P-T valve regardless, as it sounds questionable. They're about $10-15, plus usually a pipe directing it to the floor or even a nearby floor drain (which you can probably re-use).
It's a safety device that prevents your tank from over-pressurizing (which in very extreme cases can actually cause an incredibly powerful explosion -- check youtube for some entertaining mythbusters clips). You also don't want it to trip accidentally, as it will pour a lot of very hot water out and will not stop until the P-T valve shuts itself off automatically (unlikely if it's broken), or someone shuts off an upstream valve. If your floor drain is clogged, or gets overwhelmed, you have a flooded basement/house.
If your home has high water pressure, then you need to have a pressure regulator valve installed just after the main shutoff, and possibly an expansion tank to handle pressure from the expanding water in the hot water tank once that valve is installed (you would no longer have expanding water going back into the mains once the valve is installed).
To find out, pick up a tester from your local HI store, they are relatively cheap:
If you're outside of the normal 40-65 psi range, then the pressure regulator valve you need will look something like this:
It can be a DIY job if you are comfortable with cutting and soldering pipes.
If, on the other hand, the gauge reads below 65psi when the water tank's TPR is leaking, then it may be going bad. You should also verify that the water heater's temperature is not set too high before replacing this valve.
