Check vavle on domestic side of hot water heater.

[th3w01f]

Yea most likely. But small expansion tanks like that are really cheap. I feel like I got one at home depot one time I the 20-40$ range, but could be wrong. Just remember the more times a relief valve pops off the greater the chance it won't reset

My worry is my lack of DIY skills and not the cost (although I don't want to pay the $500+ I'm sure a plumbing company would charge to install an expansion tank on Sunday). I've never soldered a pipe and I'm not sure this is the time to start. . I'm confident I could cut the check valve out and use compression fittings to get it back to the way it was.

[Ramsker]

My worry is my lack of DIY skills and not the cost (although I don't want to pay the $500+ I'm sure a plumbing company would charge to install an expansion tank on Sunday). I've never soldered a pipe and I'm not sure this is the time to start. . I'm confident I could cut the check valve out and use compression fittings to get it back to the way it was.

I put in an expansion tank myself a few years ago . . . it really wasn't too hard and I'm a weekend warrior plumbing noob at best. That was especially true at that time. I just used Shark Bite fittings for that, because it was easy to do and in that application, in a utility room, I can easily monitor and if there is ever a leak I can pop on a new fitting.

Since that time I have tried to learn to solder and am much more comfortable doing that, but I would still probably keep the compression fittings on this if I ever need to work on it. Basically just a "T" off the water line and a coupling for the short pipe to the tank. Then just support it well with some strapping.

[th3w01f]

Basically just a "T" off the water line and a coupling for the short pipe to the tank. Then just support it well with some strapping.

Hmmm, a T doesn't sound too bad, I was trying to figure out how to get it fully inline with the short run of pipe that is horizontal.

[Ramsker]

Hmmm, a T doesn't sound too bad, I was trying to figure out how to get it fully inline with the short run of pipe that is horizontal.

Mine looks like this. I cut into the line to the water heater and put in the T. Then a short piece of pipe that connects into another Shark Bite that has the fitting on one end and a threaded adapter for the tank on the other.

[Great-Kazoo]

My worry is my lack of DIY skills and not the cost (although I don't want to pay the $500+ I'm sure a plumbing company would charge to install an expansion tank on Sunday). I've never soldered a pipe and I'm not sure this is the time to start. . I'm confident I could cut the check valve out and use compression fittings to get it back to the way it was.

If you're that confident for the task, you're more than capable of installing the tank

There's no time like the present to learn.

Every home repair and improvement we did started with saying what the hell, have to learn some time.