"Ed,

 Don't run a heating blanket. Nos is an oxidizer (as I'm sure you know) and it would just be the bottle exploding from pressure. Have you ever seen the result when a water heater blows from excess pressure and a stuck relief valve? Truly amazing. When dealing with anything under pressure there are risks.

Bill Jepson "

 

Let me try to connect you with a web page that shows just exactly what happens. As a licensed plumber, let me assure you, that you should NEVER plug or restrict your T&P valve on yout water heater or boiler. This was a very small water heater used in this experiment, about a third the size of most reisdential water heaters. Will give you a new respect for what is sitting in your basement or utility room. Enjoy. Sorry its off subject...

http://www.waterheaterblast.com/

Ben Schneider