The temperature and pressure relief valve (T&P Valve) is a crucial safety feature of your water heater. This valve allows the hot water heater to automatically release water should it get too hot or the pressure rise too high. Failure of T&P valve is the most common explanation for water heater explosions and is usually the result of sediment buildup or corrosion.
Testing of the T&P valve should be performed at least once a year and is simple enough to be performed by the homeowner. Make sure that the shut-off valve to the heater works prior to testing the T&P as the valve may stick in the open position if it is faulty!
To test your T&P, simply lift up the lever part way and allow it to quickly close. You should hear a little water run through it when it opens and it should snap shut and stop dripping after a minute or two. If you do not hear any water when it is operated, or it continues to drip after a few minutes, then the T&P is not functioning properly and should be changed immediately. If this is not something that you feel comfortable doing, then contact a licensed plumbing company like A+ Plumbing Professionals.