I bought a hot water tank last year. After 3months the tubing above the tank burst.?

The plumber replaced the tubing with a whiter stiffer tubing and said that the pvc tubing we have is obsolete then 4 months after that it burst again but further from the new tubing. Since then I had another leak. I would like to find out if there is a different pressure from different tanks and do I have replace all my tubing to accomadate my new tank? I replaced my 30 gallon to 40 gallon.