"If it aint broke dont fix it is my mantra, does it ring true in this case?".

When you hear a VERY loud noise and notice that you have a new skylight you will have your answer.

a video for your enjoyment

When you have a closed plumbing system, and you know it is cause the check valve makes it a closed system, code requires a thermal expansion device for a reason... SAFETY. A thermal expansion tank is less than $50 @ HD or Lowes and the T is already there.

Learn about thermal expansion by... clicking here

If you are monitoring your system pressure with a single needle gauge you may never see the huge psi spike cause it is transient. You need a gauge with a tattletale needle. Also, your T&P valve may be bleeding off or burping the pressure spikes and that is bad for the T&P valve. Repeated over-pressurization of the WH can weaken the tank and result in premature tank failure

I would buy and install a correctly sized thermal expansion tank ASAP along with a new (correct specification & EXACT replacement) T&P valve... cause the cost of having my roof fixed is much higher than the cost of a thermal expansion tank..

This post was edited by justalurker on Thu, Aug 15, 13 at 9:59

Thanks! I went ahead and put in a tank.Sized accordingly at the Watts website.

Im still confused why the previous owners had a tee installed but no tank.... Maybe the plumber gave them the option and they were just cheap or uninformed rather than some kind of mechanical reason?

knock on wood everything is OK.

But how do you know if your expansion tank has failed?

(besides your water heater turning into a rocket!)