||02-05-2012 09:58 AM
Yes, Water Heaters can go off and launch.
The T&P is the 3rd in line safety device the first 2 are the Thermostat and the ECO. After that your water heater is trying to become a steam boiler and that won't work well especially without a relief valve....
You may be able to replace the T&P but with a 21 year old water heater I'd just replace the water heater.