Tankless Water Heater Flush Questions

[alarmguy]

Tankless water heaters are rated at a given GPM of supplied hot water from the unit, at a certain degree rise......meaning the colder the water going in....to maintain the same GPM, the outgoing temp must go down. Tankless heaters work on restriction to increase the temp. In other words, the water must be slowed to increase temps.

Tank type heaters are rated at typically a 90 degrees rise, while tankless are rated at 50 degree rise, or so. If you increase the temp, the flow must decrease aswell.

No, I used to use 2 gallons white vinegar, 1 or two gallons distilled water, typically ran for 1 hour to 1.5 hours.

Flushing chemicals are a waste of money IMO.

Wow!
Great explanation! Thanks!

This explains why the cold winter water supply going into the tankless isn't as scalding hot as when the warm summer water supply going in. Even though the default 120 temp is the same that is not like setting the thermostat on your HVAC system. Increasing it to 125 made me happy, once summer arrives I will most likely mix more cold water at the shower.
To be clear it's just that extra "sizzling" hot water I like in the shower its all seasons it was always enough as my wife never uses straight hot water when she takes a shower winter or summer. So it's not like I doubted the heater.

2 gallons I assume white vinegar and distilled water.

 

[John Galt]

I have a Navien combi system that provides instantaneous hot water and hot water to my house heating system, three zones. The heating and hot water systems are separate water systems but a common gas heater and controls. They factory service folks who flush my system use a solution called Haymaker. Found on Amazon. He said Navien does not recommend acetic acid and prefers citric acid based solutions.

Last factory service cost $300 but it is a complicated system.

 

[JeffKeryk]

Vinegar seems like a 1950's solution. There has to be something more specialized for this. It doesn't seem like it would be strong enough to remove scale build up. Does the company have any guidelines or do they recommend Vinegar?

Noritz says you can use either, but if you use a solution, make sure it is safe. See the 20 second mark of the video.

 

[JeffKeryk]

2 gallons I assume white vinegar and distilled water.

I used 3 gallons of vinegar.

 

[alarmguy]

I used 3 gallons of vinegar.

SO no water mixed in I assume

 

[JeffKeryk]

SO no water mixed in I assume

I had 4 gallons on hand, but used 3 in the 5 gallon bucket. Some say refresh 1 gallon half way through, but I did not bother. Make sure you shut off the gas. Again, easy procedure.

 

[burbguy82]

2 gallons I assume white vinegar and distilled water.

yeah, it depends on the unit size, but normally 3-4 gallons will do one unit. Full vinegar is fine, I just did not want to strong of a solution in customers heaters, so I would dilute with distilled water.

Some unit's internals are a copper alloys some are stainless..........changes the requirement for certain acids.

Biggest thing is to rise the pump in the bucket after you are done. The heater will get rinse just fine when you turn the water on.

 

[CarLuver]

i have had my tankless for close to 20 years . how often you flush it depends on the quality of the water . i used to flush mine every year the first couple of years , but i found nothing came out on every flush. so i just do it every 3 years . The quality of the water in a my area is excellent .

i just get 4 gallons of vinegar ,fill 5 gallon bucket drop my pump in and hook it up . mines come out green a little , but no calcium etc is ever seen .

 

[JeffKeryk]

i have had my tankless for close to 20 years . how often you flush it depends on the quality of the water . i used to flush mine every year the first couple of years , but i found nothing came out on every flush. so i just do it every 3 years . The quality of the water in a my area is excellent .

i just get 4 gallons of vinegar ,fill 5 gallon bucket drop my pump in and hook it up . mines come out green a little , but no calcium etc is ever seen .

Mine came out pretty clean this time. It was almost 16 months? Piece of mind...

 

[burbguy82]

i have had my tankless for close to 20 years . how often you flush it depends on the quality of the water . i used to flush mine every year the first couple of years , but i found nothing came out on every flush. so i just do it every 3 years . The quality of the water in a my area is excellent .

i just get 4 gallons of vinegar ,fill 5 gallon bucket drop my pump in and hook it up . mines come out green a little , but no calcium etc is ever seen .

Well, of course like anything else, it can be overdone. If you have no nasties come out, then you likely do not need to do the service.....again water quality is key.

If even every 3 years, nothing comes out, then it is likely you could extend the interval.

The green stuff is a protective crystal coming off the inside of copper alloy tubing.......not necessarily a good thing to remove.

 

[alarmguy]

Well, of course like anything else, it can be overdone. If you have no nasties come out, then you likely do not need to do the service.....again water quality is key.

If even every 3 years, nothing comes out, then it is likely you could extend the interval.

The green stuff is a protective crystal coming off the inside of copper alloy tubing.......not necessarily a good thing to remove.

You've been a great source of information. Thanks.
SO let me ask you this, brand new home 3 years ago. Rinnai water heater for our 1800 Sq Ft retirement home, we notice no loss what so ever in performance two showers can run the same time or the washer and shower, not even a swing in temperature. I am impressed because at the time I really wanted a good old propane hot water tank heater.

SO 3 years now I never cleaned the coils. I honestly dont know nor have I seen any plumbers cleaning the coils of what must be 100s of homes in our community though much of it new. SO it may not be a problem in this area though I know from past experience decades back my dad would clean the coils in a hot water boiler as some of that gunk was do to public water treatment to protect the pipes.

I say plumbers because I think I am one of few nowadays that performs his own maintenance on the house, cars boat and bike.

Do I take a stab in the dark and clean it to see what comes out or do I wait longer. Also if you can, based on this answer to someone, please give me you exact recommendation of what to put in a five gallon pail to circulate through the coils.
Again, thanks for your input in this thread.

 

[KrisZ]

You've been a great source of information. Thanks.
SO let me ask you this, brand new home 3 years ago. Rinnai water heater for our 1800 Sq Ft retirement home, we notice no loss what so ever in performance two showers can run the same time or the washer and shower, not even a swing in temperature. I am impressed because at the time I really wanted a good old propane hot water tank heater.

SO 3 years now I never cleaned the coils. I honestly dont know nor have I seen any plumbers cleaning the coils of what must be 100s of homes in our community though much of it new. SO it may not be a problem in this area though I know from past experience decades back my dad would clean the coils in a hot water boiler as some of that gunk was do to public water treatment to protect the pipes.

I say plumbers because I think I am one of few nowadays that performs his own maintenance on the house, cars boat and bike.

Do I take a stab in the dark and clean it to see what comes out or do I wait longer. Also if you can, based on this answer to someone, please give me you exact recommendation of what to put in a five gallon pail to circulate through the coils.
Again, thanks for your input in this thread.

I would not wait until there is a flow problem, because by then a normal flush may not be strong enough to dissolve the calcium buildup.

However, you can take a look at the shower heads and appliances like a kettle and how much build up they have. That should be a pretty good estimation of your water hardness levels.

 

[alarmguy]

I would not wait until there is a flow problem, because by then a normal flush may not be strong enough to dissolve the calcium buildup.

However, you can take a look at the shower heads and appliances like a kettle and how much build up they have. That should be a pretty good estimation of your water hardness levels.

Good point, we have no buildup. Nothing at all I also have an aquarium so I test both the aquarium water and the tapwater and it’s soft water.
Actually, so soft I add some crushed coral to the filter of the freshwater aquarium to increase the calcium level a little bit

But still, I know public water supplies, and I forgot what it is that they add to the water in order to protect the pipes
I’m just unsure if my County does it or not
Typically, when that chemical comes in contact with a hot heat exchanger it coagulates over time on that exchanger
Kind of sometimes like a car heater core

 

[KrisZ]

Good point, we have no buildup. Nothing at all I also have an aquarium so I test both the aquarium water and the tapwater and it’s soft water.
Actually, so soft I add some crushed coral to the filter of the freshwater aquarium to increase the calcium level a little bit

But still, I know public water supplies, and I forgot what it is that they add to the water in order to protect the pipes
I’m just unsure if my County does it or not
Typically, when that chemical comes in contact with a hot heat exchanger it coagulates over time on that exchanger
Kind of sometimes like a car heater core

I'm not familiar with said chemical. Perhaps others know what that is.

 

[alarmguy]

I'm not familiar with said chemical. Perhaps others know what that is.

I found it but maybe not as big of a deal as I originally thought back when I was growing up.
On Long Island at the time, it was a sludge like material and that would be the ortho phosphates
I guess, I can be completely wrong and it just might be mineral sticking to the hot surface, but I know this some validity to it
https://olympianwatertesting.com/what-are-orthophosphates-the-chemical-that-protects-your-pipes/


https://brodychemical.com/blogs/guides/water-treatment-chemicals

 

[KrisZ]

Found this about orthophosphates. Seems like they can combine with calcium and magnesium and form deposits, but I think we just take it as normal calcium deposits anyways, since the appearance can be white or grayish.
So if your water is already soft an doesn't have lots of calcium or magnesium, you will be safe.

https://www.hoffmannbros.com/mineral/orthophosphate

 

[burbguy82]

You've been a great source of information. Thanks.
SO let me ask you this, brand new home 3 years ago. Rinnai water heater for our 1800 Sq Ft retirement home, we notice no loss what so ever in performance two showers can run the same time or the washer and shower, not even a swing in temperature. I am impressed because at the time I really wanted a good old propane hot water tank heater.

SO 3 years now I never cleaned the coils. I honestly dont know nor have I seen any plumbers cleaning the coils of what must be 100s of homes in our community though much of it new. SO it may not be a problem in this area though I know from past experience decades back my dad would clean the coils in a hot water boiler as some of that gunk was do to public water treatment to protect the pipes.

I say plumbers because I think I am one of few nowadays that performs his own maintenance on the house, cars boat and bike.

Do I take a stab in the dark and clean it to see what comes out or do I wait longer. Also if you can, based on this answer to someone, please give me you exact recommendation of what to put in a five gallon pail to circulate through the coils.
Again, thanks for your input in this thread.

Some plumbers will not perform the flushing service for liability reasons.....maybe that is why you do not see it around your area....that compiled with you good water quality.....you may not need to flush the heater out.

If it were me, I would do the service, but that is me.....if nothing other than to gauge whether or not it was needed or to formulate a timeframe for followup service.

If you are up to the task, drive on.

As to the solution, white vinegar is what I have used and distilled water. I have never purchased "Haymaker" or other products for this purpose. Maybe get 3 gallons white distilled vinegar, pour 3 in the bucket, see if it is enough.....if not, pour in distilled water to top off...., if so, let it roll. Maybe a gallon is stored in the "tank" of the "tankless" heater....plus tubing.

Their is also a screen of some kind on most units on the incoming side of the heater. Be sure to remove this screen after cleaning, clear out debris, and replace.

@walterjay ?

 

[Sam_Julier]

We have a Bosch On-Demand unit with a pilot light. It’s over 20 years old.

Every two years I descale it with vinegar with the pilot light out. That’s it.

As long as Ms J gets hot water for her bath we’re good.

 

[jtwrace]

What pump are you using? I need to do this to my system.

 

[mk378]

The heat exchanger will make sizzling sounds like a tea kettle when it is has scale inside.