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Question DetailsAsked on 7/22/2014

how much to install a new expansion tank on water heater

Tank is almost new.........they didn't put a new expansion tank on.

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3 Answers


Expansion tank does not have to be replaced same time as water heater - commonly go 6-12 years and frequently longer between replacements. If it is not leaking or rusting and plumber did not say to replace it, I would not.

With a new visit, probably $75-150 labor (minimum charge) and about $30 for the tank.

Answered 6 years ago by LCD


I would also add that some folks do not favor use of expansion tanks or even recommend against them as unneeded.

However, depending upon the brand of water heater, the conditions for warranty coverage may well demand that an expansion tank be installed. I have a Reliance Gas tank with 12 year warranty that requires an expansion tank or the warranty is void.

I have found plumbers that do not know that expansion tanks can be a condition of warranty coverage so it is important for consumers to read the very fine print of your warranty to see if it become void in the absence of an expansion tank.

Source: Reliance 1212 Warranty Booklet

Answered 6 years ago by SeaJay


That is a new one on me about water heater warranties requiring expansion tanks in all cases or the warranty is void - makes no technical sense, but when you get the lawyers into the picture ...

The reason for expansion tanks, other than being required by code in some areas, is that IF you have a backflow preventer or pressure regulator on the incoming water pipe between the public water pipes and the water heater, when the heating water expands there is no place for it to expand to, and since water is essentially incompressible it pressures up your hot water pipes and can cause leaks or rupture of the hot water tank. I have seen several cases where pipes or water heaters split due to the pressure where the backflow preventer was close to the heater and the hot water pipe runs were short, so the expansion tank IS necessary if you have backflow preventing devices on the piping.

IF you do NOT have a backflow preventer or pressure regulator, then as the heating water expands, the hot water in the tank can push back into the incoming cold water line to accomodate the expansion.

Because more and more codes are requiring backflow preventers on house systems (usually either just inside the house or at the meter), it is becoming more common to see them required on hot water heaters as well as boilers.

Answered 6 years ago by LCD

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