Tankless Water Heater Flush Questions

[JeffKeryk]

I love our little Noritz Tankless. Made right here in California!
I used 3 gallons of Walmart vinegar; some say to use a specialized solution. This was a 15 month flush interval...
Perhaps the plumbers on our forum might offer their thoughts?

After the flush, I realized I failed to shut the gas valve off; it seemed to work anyways. Did I mess up? Am I fired?

Thanks in advance. Appreciate you.

 

[meep]

I’ve done this a few times. Good on you for doing it. The plumber who installed mine actually recommended doing it hot - it’s not like the burners get these over 120F anyway, and once the water is up to temp they won’t fire. The only exception I could see is that the noritz is capable of doing a bypass if it feels like it needs to do that to keep the temperature dialed in, but regardless you had the solution in the tank.

BTW I’ve had both noritz and Rinnai. My house came with an unmaintained Noritz and the plumber I use favors Rinai. Of the two, I liked the Noritz better. Rinai may have an easier design for repair, but the Noritz kept a rock-solid temperature. The Rinai fluctuates in its use. Noritz also allows a slightly higher setpoint than Rinai. You absolutely can override the Rinai setpoint to reach 120, but it shortens the predicted lifespan and much over that they will deny warranty.

Every time I’ve done it, the water turns a little bit blue but there’s no rust or scale or anything.

 

[JeffKeryk]

@meep I bought the Noritz for 2 reasons:

1. I asked our company's facilities manager what brand they used and what to buy; he recommended Noritz right off.
2. Noritz is headquartered in California.

 

[DCDG]

i don't think its an actual necessity to run a flush with the gas supply off. it's more the case of the unit accidentally being used and heating up the flushing agent being used in your case the vinegar. if someone opened up a hot tap on a faucet not knowing you were flushing the unit.

 

[Hall]

some say to use a specialized solution

No need. Almost all of these "specialized solutions" will be mixtures of vinegar or citric acid or something relatively basic, but packaged like it's some proprietary, advanced cleaning chemical.

 

[mk378]

Water lines on the top is an unusual design.

Flushing is always done cold. Hot flush solution will cause corrosion.

You need to turn the heater off with the control panel, but leave the AC power connected. This opens the electric valves inside the heater so the flush will flow through the heat exchanger. Since the control is shut down, it wouldn't matter if the gas supply is left on, but a very good precaution to turn it off.

 

[wander2039]

On our Rhinna I just unplug it. Flushed it 5 times, typically the first weekend in January. Guessing that make is different.

 

[fsdork]

I don't have anything to offer in terms of the hardware and procedure, but I discovered cleaning vinegar a while back. It's double the acetic acid concentration as compared to standard white vinegar, so that makes for less liquid volume you have to haul home from the store - just mix it to the required concentration on site.

 

[JeffKeryk]

Water lines on the top is an unusual design.

Flushing is always done cold. Hot flush solution will cause corrosion.

You need to turn the heater off with the control panel, but leave the AC power connected. This opens the electric valves inside the heater so the flush will flow through the heat exchanger. Since the control is shut down, it wouldn't matter if the gas supply is left on, but a very good precaution to turn it off.

A few years ago Noritz designed this model to easily replace a tank style water heater by putting the water lines on top.
I think they call it the "EZ" line.

 

[KrisZ]

Water lines on the top is an unusual design.

Flushing is always done cold. Hot flush solution will cause corrosion.

You need to turn the heater off with the control panel, but leave the AC power connected. This opens the electric valves inside the heater so the flush will flow through the heat exchanger. Since the control is shut down, it wouldn't matter if the gas supply is left on, but a very good precaution to turn it off.

Not sure where you're getting the risk of corrosion from, Most if not all of the tankless water heaters have copper heat exchangers. There is no corrosion issues at all. And hot cleaning actually speeds up scale removal. You may want to dial the temp down as to not damage the submersible pump and scold yourself, but that's about it.

Hot flushing is about keeping the operator safe, not the equipment.

 

[mk378]

Vinegar or anything acid is active on copper. The reason the used flush turns blue is copper dissolved in it.

 

[KrisZ]

Vinegar or anything acid is active on copper. The reason the used flush turns blue is copper dissolved in it.

At 10% concentration that I used, the water never turned blue for me. Perhaps if you use the 30% concentration, it may be too strong. Regardless, the contact time is too short to affect the copper piping, otherwise manufacturers would not recommend this cleaning method.

 

[burbguy82]

@JeffKeryk

Your water heater is a fairly simple unit, as most of them are. They look complicated compared to a tank, but not really. ALL gas fired tankless heaters work off of the following steps...in this order...basic theory.

1.) Flow is sensed by the flow meter located somewhere in the cold side, telling the computer that there is a demand for hot water.
2.) The computer starts the spark igniter to ignite gas
3.) A solenoid valve opens, allowing gas to flow to the burn chamber=fire
4.) Exhaust gas sensor verifies combustion to a predetermined value based on the output and demand

If any of the above do not happen, an error code will be shown on the display.

Some units have more steps, but none have less. That being said, some type of power must be hooked up to the unit to power the computer and igniter......without that, nothing will function.

So while the appliance valve, located on the exterior was on, the solenoid valve, which is normally closed.......was closed, assuming you turned power off.

Flushing a tankless unit greatly increases reliability and efficiency. Once a year depending on water quality is typical. Flushing, as it pertains to reliability, is step#1 as noted above......The flow meter gets crusty and can't move, thus....no spark, no gas, no fire.

Hope this helps.

 

[JeffKeryk]

@JeffKeryk

Your water heater is a fairly simple unit, as most of them are. They look complicated compared to a tank, but not really. ALL gas fired tankless heaters work off of the following steps...in this order...basic theory.

1.) Flow is sensed by the flow meter located somewhere in the cold side, telling the computer that there is a demand for hot water.
2.) The computer starts the spark igniter to ignite gas
3.) A solenoid valve opens, allowing gas to flow to the burn chamber=fire
4.) Exhaust gas sensor verifies combustion to a predetermined value based on the output and demand

If any of the above do not happen, an error code will be shown on the display.

Some units have more steps, but none have less. That being said, some type of power must be hooked up to the unit to power the computer and igniter......without that, nothing will function.

So while the appliance valve, located on the exterior was on, the solenoid valve, which is normally closed.......was closed, assuming you turned power off.

Flushing a tankless unit greatly increases reliability and efficiency. Once a year depending on water quality is typical. Flushing, as it pertains to reliability, is step#1 as noted above......The flow meter gets crusty and can't move, thus....no spark, no gas, no fire.

Hope this helps.

Appreciate your well written response! Wow!
A bit more context... I did not power down the unit. There is a blue descale wire labeled "FLUSH" near the circuit board that you connect together. It sets a timer on the display to 60 minutes ("C60" display) and starts to countdown. I realized I did not close the gas port upon hose removal; the hot hose was warm. Vinegar did not get to 120*. You can see the blue FLUSH connector at the top of the HF bucket and "C57" timer display in the image from post #1.

Again, I appreciate your time. Outstanding.

See the beginning of this video and then the 2:20 point:

 

[burbguy82]

Appreciate your well written response! Wow!
A bit more context... I did not power down the unit. There is a blue descale wire labeled "FLUSH" near the circuit board that you connect together. It sets a timer on the display to 60 minutes ("C60" display) and starts to countdown. I realized I did not close the gas port upon hose removal; the hot hose was warm. Vinegar did not get to 120*. You can see the blue FLUSH connector at the top of the HF bucket and "C57" timer display in the image from post #1.

Again, I appreciate your time. Outstanding.

See the beginning of this video and then the 2:20 point:

Likely the yellow plug turns off gas or otherwise a "bypass sensor" mode. Some units want no power, some you have to key in a mode to flush, etc. They are all different.

 

[alarmguy]

Our purchased new Home is now at the three year mark. I never flushed the Rhinna I guess I will someday. We have soft water here.

I guess when I do, I will look more into what is best to use.
In the old days, my dad would flush the hot water coil in the oil burner with muriatic acid.

We don’t have any fluctuation, I mean zero fluctuation in the water temperature taking showers.

I like a super hot shower and I have noticed in the cold winters. The water temperature is just not quite there for me. My wife says it’s fine and doesn’t notice a difference because she doesn’t turn it all the way hot.
Anyway, the maximum preset is 120 unless you take an extra step to override that limit.
You can go up to 140 but I only bumped it up to 125 as that’s all I need

 

[JeffKeryk]

Our purchased new Home is now at the three year mark. I never flushed the Rhinna I guess I will someday. We have soft water here.

I guess when I do, I will look more into what is best to use.
In the old days, my dad would flush the hot water coil in the oil burner with muriatic acid.

We don’t have any fluctuation, I mean zero fluctuation in the water temperature taking showers.

I like a super hot shower and I have noticed in the cold winters. The water temperature is just not quite there for me. My wife says it’s fine and doesn’t notice a difference because she doesn’t turn it all the way hot.
Anyway, the maximum preset is 120 unless you take an extra step to override that limit.
You can go up to 140 but I only bumped it up to 125 as that’s all I need

AG, do the descale flush. You just might sleep better. Pretty easy as the hour goes by pretty fast. Vinegar is fine; use one of the available products if you wish.

Perhaps @burbguy82 can chime in on the better flush to use?

 

[JWC86]

I use strait vinegar in mine and let it heat the solution up first and then I unplug it and let it circulate for 2-4hrs.

I do this at minimum once a year but many years I’ve done it twice.

I’ve been doing it like this for 12 years on the same heater, am I doing it wrong?

 

[burbguy82]

I have noticed in the cold winters. The water temperature is just not quite there for me

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.

Perhaps @burbguy82 can chime in on the better flush to use?

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.

 

[97prizm]

I love our little Noritz Tankless. Made right here in California!
I used 3 gallons of Walmart vinegar; some say to use a specialized solution. This was a 15 month flush interval...
Perhaps the plumbers on our forum might offer their thoughts?

After the flush, I realized I failed to shut the gas valve off; it seemed to work anyways. Did I mess up? Am I fired?

Thanks in advance. Appreciate you.
View attachment 332842

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?