We installed a new water heater 8 years ago, and since then I've ignored it. It's an indirect model, heated by the same gas boiler that heats our house, and it has done its job well. When I was thinking about heat pumps, however, I reread the manuals for our existing system and noticed that the manufacturer recommends checking the anode annually. The idea is that water will corrode metal, but prefers some metals to others, so if you put in a chunk of tasty sacrificial metal you lose that instead of the tank walls.

Once every eight years is not annual, but better late than never!

Since it had been quite a bit longer than anodes usually last, I preemptively ordered a new one. When it arrived I warned people that I was going to be shutting off the hot water for a while, but as soon as I took off the insulating cap for the old anode it was clear I didn't have what I needed. It used a 1 3/4" hex head, recessed, and I didn't have any sockets close to that large. Neither did the hardware store: I had to order one.

I think the manufacturer realized this was silly: the replacement anode came with a 1" head, and reading their documentation they switched to 1" in in 2021.

Once I had the right-sized parts I turned off the system, shut off the incoming water, opened a hot water tap to break the vacuum, hooked up a hose to the drain port, and got it draining. I went and did something else for a long while, and when I came back I started on the anode. The first problem was that the thermostat is immediately in front of the anode port:

I needed to disassemble this more than I wanted to get it out of the way.

Once it was clear, it was hard to get the anode rotating. I needed a cheater bar (a pipe slipped over the breaker to extend it). When it came out I was surprised in two ways:

The old anode had been entirely consumed. Here is the new one and old one side-by-side:
Lots of water came out:

The problem was, I hadn't confirmed that the water heater had finished draining. An 80 gallon tank (two units, eight bedrooms, ten people) takes a long time to drain, and it was far from done. Luckily this is an unfinished basement with nothing that minds getting wet, and it all drains to a sump.

After the top finished draining out the wrong hole, and then the bottom finished draining out of the right hole, I cleaned anode port first with a wire brush and vinegar to remove mineral deposits andthen with an old toothbrush and water to remove anything left. I applied thread sealant, and put the new anode in. It was hard to get it seated right with the threads: it is long and reasonably heavy, and it really wants to pull down.

Once it was tight again, I turned the water back on to the tank. While it filled I used a hair dryer to dry out the thermostat. After a bit I turned the power back on. We have hot water again!

I've seen myself a reminder for two years from now to check the anode again. By seeing how much has been eaten away in that time, I should be able to get a good estimate for when I should next replace it.

Overall this cost me:

$107.83: replacement anode
$16.19: 1 3/4" socket (3/4" drive)
$14.97: 1/2" drive breaker bar
$12.98: 1/2" to 3/4" socket adapter
$6.27: 1" socket (1/2" drive)
$158.21: total

Plus about three hours of my time, one in advance and two of actually doing the replacement. Since dealing with a water heater replacement is substantially more money and I enjoy doing this kind of thing, this seems worth it!

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