I feel like I understand computers pretty well, but when I do some maintenance on my tankless water heater, this is the best understanding I have:

My tankless water heater is a Navien NPE-240A natural gas water heater. That's not an endorsement, since I didn't pick the model; the technician who installed it asked a few questions about my family's desired water demands, then he picked it out. My old water heater was gas, so this one is gas. That said, it works great! But how does it actually work?

Fortunately, multi-modal LLMs these days are pretty good at understanding pictures, so I uploaded this image and asked it to explain everything for me. It mostly did! It even did a half-decent job labeling the picture, but below I did a better job.

Before LLMs, I would probably scour the internet hoping some blog post would explain it for me in layman's terms. I can't parse the dense technical manuals without taking a course in thermodynamics. LLMs really are game-changers.

I got this tankless water heater years ago after my regular 40 gallon water heater died. It cost a total of $3,100 for parts and labor to get it installed. I'm very happy with that price and expect it to last for decades with regular maintenance.

Since the tankless water heater got installed in my house's crawlspace, I was able to reclaim some floor space where the old water heater once stood. I converted that area into a bunch of shelves. At the time of this writing, my house is worth roughly ~$238/sqft, so reclaiming 4 sqft justifies almost $1k of the price!

How to flush Matt's tankless water heater

Once a year, I need to flush it out to clean it. Since it's so infrequent, I have to read the instruction manual every time as if it's the first time. So the rest of this post isn't for you, it's for me! I'm only writing for myself after all. Feel free to stop reading now unless you have a tankless water heater I guess. I'm willing to entertain any offers to do this for me.

Step 1: Gather the supplies

• 5 Gallon Bucket
• Water pump
• Vinegar
• Little pipe cleaner
• Bowl to drain water heater
• Headlamp
• Towels

Tip: Just keep these near the water heater all the time. Except the vinegar, it's one-time-use

Step 2: Turn off the water main

Nobody will be able to use faucets for the next hour-ish, so be sure to top up your water bottles, and fill a big bowl/sink with water for random water needs. Also, you can only flush each toilet once, so... prepare for that too. We take faucets for granted so don't be surprised if you accidentally forget at least once during this process.

Step 3: Turn off the gas to the hot water heater

This is true for all plumbing: if the valve is perpendicular to the pipe, it's off.

Step 4: Drain the water heater

Put a big bowl under the water heater, then start unscrewing everything pictured to let it drain. Clean the filters you unscrewed with the pipe cleaner with the water draining into the bowl.

Empty the bowl when it gets full. It shouldn't overflow (much).

Step 5: Prep the pump

1. Pour vinegar into the bucket
2. Put the pump in the bucket
3. Connect the blue hose to the blue water outlet, and to the top of the pump (I always keep it connected to the pump)
4. Connect the red hose to the red water outlet, and the other end in the bucket.

Step 6: Let it run

Plug in the pump and it will start running immediately. Let it go for at least 45 minutes. Unplug the pump when it's done.

Step 7: Flush out the vinegar with water

At this point, the instruction manual wants you to keep the hoses attached and run fresh water through everything. If you're using a cleaning solution, that's probably for the best, but this is vinegar, so it's less critical to keep it out of your pipes. We'll flush it out this way instead:

1. Turn the water main back on
2. Remove the blue hose and close the blue pipe by screwing the cap back on
3. Take the pump out of bucket, but leave the red hose in the bucket
4. Slowly open the blue valve. This will run fresh water through the water heater and out the red hose into the bucket

1. Fill the bucket, then shut off the blue valve to stop the water flow. Drain the vinegary bucket
2. Remove the red hose and close the red pipe by screwing the cap back on
3. Open red and blue valves
4. Run hot water in the sink nearest to your hot water heater. For me it's the basement bathroom. Do this for five minutes
5. Plug the hot water heater back in. Turn the gas back to on

Step 8: Clean up

Put the pump and hoses back in the bucket. Towel off any standing water. Maybe one day I won't spill any water during this process, but it hasn't happened yet. Set a reminder for next year with a link to this page.