Are you talking about the whole-house kind of water heater, or the small per-shower water heater box inside a shower area? The latter was my experience in Thailand, but I think this thread is about the former.
https://www.homeappliances.hitachi.com/th/products/shower-heater/image/category_sh1.jpg
I think they are fine, if installed and maintained properly. Last month I looked at an insurance claim where one had failed. It was completely clogged with scale and could not be saved. Just a few years old, no replacement core to be found.
My plumber insists they need to be descaled yearly and absolutely should be run on soft water. This is Calgary, Alberta and the water is very hard. Some municipalities are going to have soft water, so maybe you can get away with out a softener and descaling if so.
If the delay for the cold water in the pipes to clear is an issue, tanks have the same problem, but there are solutions. Many come with built in, scheduled recirculation pumps. You need a return line installed to the intended fixtures, but the water is hot immediately.
Mt wife & I bought a house in Chester (UK) about 4 years ago. As part of the renovations & upgrades before we moved in, we replaced an ancient tank hot water system with a new gas boiler which provides on-demand hot water as well as running the radiator central heating.
It has worked fine for us so far. We can bathe one after another without any worries of drawing a tank down. Delay to get fully hot water from the tap is something like 15 to 20 seconds, though it’s not a big house. Not sure how that would compare with a tank system, since we never lived there with the old one. Likewise, can’t make any comparisons of running costs. But overall, we have no complaints.
We live in a 6-unit condo building that was new construction about 12 years ago with Rinnai tankless (natural gas) water heaters. You are supposed to have them serviced every year. We didn’t know that, and got a new unit (another Rinnai) about a year ago.
Overall, it’s ok. It saves a lot of space, which is good in a condo. It takes a while to get hot for a shower first thing in the morning, but it’s nothing extreme, and not objectionable. The only thing I find strange, and I’m not 100% sure it’s because it’s tankless, is that it’s hard to fine-tune the temperature at the faucet. It wants to be really hot or lukewarm. If you want a small amount of warm water dribbling in the kitchen (which is how I like to rinse dishes), it’s not amenable.
The latter. Sorry, I thought that was the subject.
Tankless water heaters do not have anode rods.
Regular tanked water heaters do have anodes. They can be tough to break loose, though. You have your choice of aluminum (smooth top) and magnesium (weld blob). Replace like for like.
Of course.
My comment was directed at MandaJo’s comment directly before mine.
Sorry, read out of context.
I’ve been following this thread and check in every now and then. I have issues with the tankless heaters, or more accurately the installation, but I’ve stayed out of the debate so far.