OK to start I had an outside faucet leaking and 2 toilets that needed the flappers replaced got all 3 things repaired the same day as the repairs the T&P valves started popping off for just a second and then closes. So I replaced the T&P valve. I thought this had something to do with my washer running, but now I'v noticed that any time hot water is run when the tank fills back up the T&P valve pops. The hot water heater was replaced in 2004 we have lived here for 25 yrs with no problem. What could the problem be??? And why did it start all of a sudden??? And how do I fix it ???

Your water pressure is too high and as the tank heats, the thermal expansion of the water increases the pressure inside the system. You need a pressure reducing valve and a thermal expansion tank installed. Outside faucets generally use a compression stem to stop water flow, so it requires much higher force to stop water flow, hence why they get torn up and leak. High pressure also tears up fill valves in toilets, and any other compression stem. Chances are that you have had a problem for some time, but the old water heater's t+p valve was stuck and didn't do its job.

It just started because the excess pressure was being released at the leaking frostproof. Now the water has nowhere to go except the T + P valve.