stoker-man wrote:The expansion tank sounds hollow when you rap it with your knuckles. If you have an increase in pressure along with an increase in temperature, check the circulator. If the temperature doesn't increase, check the coil, as stated.
It should sound solid above the seam and hollow below it. If it sound solid top to bottom, then it for sure needs to be replaced.
Another test is to QUICKLY depress the Schrader valve. You don't want to bleed off the factory charge. If ANY water comes out, the tank is dead.