Why do the water heater sound like it is filling up? ONe note is that water is coming from the relief pressure line

Why do the water heater sound like it is filling up? ONe note is that water is coming from the relief pressure line

Your T&P valve has opened up and is allowing water to exit outside. If you have a sprinkler system or a backflow preventer you must install a expansion tank, (see image) to prevent this from happening. If none of the above then try jiggling the lever to see if it stops. No? Then shut the power off to the water heater and frain it downb past the T&P Valve and replace the valve. Don't forget to wrap the threads with Teflon Tape. Good luck and thank you for rating my answer. Tom