This exact issue just happened to me: water heater pressure - temperature relief valve was completely open, gushing water.. We noticed the water was not super-heated, so a stuck thermostat was ruled out.. It turns out my house has a Pressure Reducing Valve which failed, causing the water pressure to jump rapidly, which triggered the T&P valve to open. .. Get a gauge and check your water pressure. If it's too high, a new T&P valve won't solve the issue.

My main question: should I do more debugging or is it safe to assume I just need to replace the T&P valve? My issue seems more extreme than most videos/articles about fixing a leaking valve and I want to know if I should investigate more serious concerns with the tank or plumbing?

Last night, a neighbor came to my door to let me know my garage was leaking significant water. I went down and my entire garage was flooded (~3 inches tall). The water was flowing full force from the copper pipe attached to the T&P Valve.

After shutting off water to diagnose, I noticed the T&P valve was fully opened (by itself). Which, after much googling, appears to be unusual. It seems like when it opens and doesn't close, it doesn't fully open (from what I gather) and should only let out a moderate amount of water (not

However, that leaves open the question of whether there is actually a water heater problem. It is possible that the T&P valve failed independent of the temperature and pressure of the water heater - i.e., just a T&P valve problem.

Yes, it is safe to assume that the T&P valve has failed and needs to be replaced. Even without the flood, a constant dripping is a sign of a problem.

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I closed it and restored water to the house, but it still has a steady drip (once every 15-30 seconds). The drop does not increase when hot water is being used, so it seems steady.

I know very little about home improvement (first time home owner). I had my hot water heater (located in my garage in the corner on a small pedestal) replaced in March of 2021 by a professional.

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It is also possible that the water heater had problems - e.g., a failing thermostat - which resulted in an actual overtemperature/pressure situation. If that is the case then the T&P valve would open, as it should to prevent a tank explosion, but that it then failed to close after relieving the overtemperature/pressure problem. If that's what happened then yes, you still need a new T&P valve, but you may actually need something else replaced - anything from a thermostat on up to the entire water heater.