The expansion tank isn’t just for the water heater. That increased pressure puts undue strain on the entire plumbing system in your home. It will cause toilet fill valves to fail, supply lines to rupture, and possibly even pinhole leaks. A lot of plumbing issues are solved by installing an expansion tank.
If it’s necessary then how did my last tank make it 20 years without one?
The expansion tank isn’t just for the water heater. That increased pressure puts undue strain on the entire plumbing system in your home. It will cause toilet fill valves to fail, supply lines to rupture, and possibly even pinhole leaks. A lot of plumbing issues are solved by installing an expansion tank.