Does anyone know what the small blue tank is on top of my hot water heater is ?

Question

I have a leak from this blue small tank on top of my hot water heater but I dont know what the blue tank is or what it does. The area is rusty and has started dripping. It is a gas heater about 3 years old.

Answer 1

This tank is for expansion of hot water and needs to be there.

Answer 2

Its a expansion tank, if you are on city water there is a double check valve in your meter crock along with the water meter and possibly a pressure regulating valve. That blue tank relieves the pressure due to expanding hot water and it does not have anywhere to go so it bust the pipes or blows the seals out of the facets and commodes.

Answer 3

It is an expansion tank. It is a place for the heated water to go so it's not expanding inside the tank and causing problems. It can be easily replaced.