Helpful Tips on Servicing a Tankless Water Heater

Hey guys!  I’ve been crazy busy Realtoring during this spring market that I really haven’t had much of a chance to get any articles out, but my husband Tony wanted to share some helpful information on servicing tankless water heaters.  I have to be honest I always tell him that I appreciate the “magic” that he makes happen… you know like running water, heat, and electricity.  Without him I’d be living in a really nicely decorated cardboard box! 

 Anyway enjoy and hopefully this helps you all out! 

 -Tony & Erin

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Many new homes are coming with natural gas or propane high-efficiency space & domestic on-demand hot water heater systems from vendors like Rinnai, IBC, and Buderus. Their efficiency ratings are typically at or over 94%. Older homes likely have traditional oil furnaces with an efficiency rating around 80-84%. Many people forget to have them serviced every year which can cut down on product life and lower its efficiency.

If you’re lucky enough to have one of these types of high-efficiency systems, or even just a tankless/on-demand hot water system (e.g. Rinnai, Rheem, Takagi, etc), it’s important to keep them serviced. CYA – consult your manufacturer documentation and/or your utility company for recommended service methods and schedules. This article will focus on some easy maintenance that homeowners can do themselves on their tankless/on-demand system.

Most tankless hot water heater manufacturers require that you have some type of water filtration system in place in order for the warranty to be valid. Even if you’re on city water, there are particles that come in through the pipes and can impact your water quality. If you’re on a private well, only mother nature can determine what is going to come into the house. These filtration systems can be relatively cheap or very expensive depending on your incoming water quality.

When we were on city water, we had this type of whole-house filter for 1 3/4 bath: GE GXWH20S

This is another model which seems fairly popular, it’s just a little bit bigger –

Now that we’re on a private well, we used Allied Clearwater ( in Kingston, NH to come and install a professional-level Entipur whole-house filter. Allied Clearwater staff is very responsive and friendly. They don’t over-engineer the solution and don’t try and upsell you on something you really don’t need.

Moving onto the main purpose of this article – doing some easy maintenance on your tankless/on-demand hot water heater. Depending on your usage and water quality, you may need to do this annually or biennially. Again, consult your manufacturer documentation and/or your utility company for recommended service methods and schedules.

What you’ll need:


1. Simply turn off the hot and cold water supplies at the bottom of the tankless hot water heater. Each supply should also have an isolation/service valve. All valves should be kept closed or off.

2. Hook one garden hose between the transfer pump intake filter (that will be submerged in the vinegar bucket) to the pump intake port.

3. Hook the second garden hose between the transfer pump output port and the cold-water service intake port.



4. Hook the third garden hose between the hot-water service output port and back into the vinegar bucket.



5. Open up both service port valves and let the water drain out into one of your buckets. It might take a couple of minutes to do. Then just get rid of the water.

6. Fill up the water bucket with new cold water and set it aside.

7. Fill up the second bucket with three to four gallons of vinegar. Submerge the transfer pump intake filter into the vinegar bucket. you should now have your transfer pump sitting somewhere outside the bucket with the intake filter hose coming out of the vinegar bucket and into the transfer pump.

8. At this point you’re ready to go. Turn on the transfer pump and keep and eye on the pump to make sure it primes and starts pumping vinegar into the tankless unit. You should see liquid dumping back out of the tankless unit and back into the bucket.

9. Let it go for about 45-60 minutes. You’ll notice that the vinegar will get dark and cloudy as it flows through the hot-water heater. Go work on another project, but don’t stray too far. Keep checking on things to make sure there’s no leaks and that the pump is still well…pumping.

10. Turn off/unplug the transfer pump and drain out the hoses as best you can into your vinegar bucket. I turned off the heater output service valve just to avoid vinegar draining out everywhere. Once things are clear, put your intake filter into the clean water bucket (see step 6), open up your tankless hot-water output service valve and turn the transfer pump back on.

11. This will force the clean water back through the pump and the tankless heater system. Let it circulate for a few minutes. There’s only three to four gallons of clean water, so you’re not going to get all the vinegar out, but you’ll cut it down quite a bit while also cleaning it out of the transfer pump.

12a. Get rid of the circulated “clean water” and repeat the process with new clean water. Do this as many times as you need to. Maybe until there’s no vinegar “taste” in the water. Obviously don’t drink it…just put a dab on your tongue to gauge whether you need to continue to flush the system with clean water.

12b. This is the easier method. You’ll need a long 50′ garden hose available to use and a way to run it out from the hot-water service valve and out somewhere. Disconnect all the pump hoses and close the service valves. From there, connect the long garden hose to the hot-water output service valve and run the hose out into the yard. With everything secure, open up the cold water inlet valve to feed new, clean, cold water into the tankless system. Ensure there are no leaks and let the cold water run through the system and out into your yard for a few minutes. You can again do a “taste test” to see if there’s any taste of vinegar left.

13. With everything clear and clean, turn off the cold water inlet valve again. Close the hot-water service valve and get everything tightened up. The last thing we need to do at this point is check the tankless hot-water heater’s inlet filter and remove any debris or items from it. 


14. The tankless/on-demand system should have a black plug that you can unscrew by hand. Attached to the plug will be the inlet filter.

Water will dribble out of the system, so have a small bucket or something to catch the water. Clean the filter and remove any debris from it. Replace the inlet filter and plug and tighten by hand. Don’t overdo it.

15. Open up the cold-water inlet valve and it’ll fill up the system. Then open up the hot-water output valve. Go ahead and turn on the hot water at the kitchen or bathroom sink and let it flow through the system. Make sure you get hot water, the unit fires on, and you have no leaks.

16. This is the vinegar after an hour of flushing through the system. YUK!

Congrats – your system is now clean and it only took you an hour and half and cost you very little $$$. It is recommended that you write down when you did this and keep a service sheet or paper somewhere near the system.

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