OT- Flushing a Tankless Water Heater

[LandArchDawg]

I live in an area with very hard water and am overdue to flush my tankless water heater. I see in the instructions to shut the gas and water off to the unit, but the only valves for water I see on mine are the hot and cold isolation valves that I hook the hoses to. Do the isolation valves provide adequate water shutoff, or do I need to shut water off for the entire house while flushing the unit?

 

[llmsudawg]

Without pics I am not sure of your exact set up. But this is how I do mine.

https://www.youtube.com/watch?v=znuACzzav_Y&ab_channel=MattRisinger

 

[LandArchDawg]

Awesome, this helps greatly! He just shuts off the isolation valves before hooking the hoses up. No other water shutoff needed.

 

[Motodawg]

I live in an area with very hard water and am overdue to flush my tankless water heater. I see in the instructions to shut the gas and water off to the unit, but the only valves for water I see on mine are the hot and cold isolation valves that I hook the hoses to. Do the isolation valves provide adequate water shutoff, or do I need to shut water off for the entire house while flushing the unit?

You shouldn’t flush your heater until you have to because once it’s descaled it can never again reach 100%. I NEVER descale until problems surface… EVER.

Incase you’re wondering, I’m a plumber and an owner of a company in the Jackson area. There’s several members on here that can vouch for me.

If you’ve already done it. Then, i guess disregard this message, if but… don’t.

 

[fedxdog]

What problems would surface that would cause you to flush the system. Asking for a friend.

 

[1msucub]

You shouldn’t flush your heater until you have to because once it’s descaled it can never again reach 100%. I NEVER descale until problems surface… EVER.

Incase you’re wondering, I’m a plumber and an owner of a company in the Jackson area. There’s several members on here that can vouch for me.

If you’ve already done it. Then, i guess disregard this message, if but… don’t.

What do you mean by 100%? Efficiency?

 

[Tomas Smid]

Don’t some manufacturers void the warranty if the units are not flushed annually as set forth in the manual!

 

[Motodawg]

What do you mean by 100%? Efficiency?

Not just efficiency, but output as well.

 

[Motodawg]

Don’t some manufacturers void the warranty if the units are not flushed annually as set forth in the manual!

Literally NEVER had this happen, not once. Ive serviced tons of them under warranty. I used to work for a company that had the AO Smith contract and i was the guy that got all of the tankless calls. I let them tell me to descale and rarely if ever before.

 

[PooPopsBaldHead]

I'm confused too. I took enough science classes to know that scaling itself is going to drag your efficiency down to the gutter. Otherwise, the manufacturer would have covered those copper tubes in the heat exchanger with calcium deposits at the factory.**

I'm sure moto has his reasons for saying what he did and maybe we misunderstood.

 

[Motodawg]

I'm confused too. I took enough science classes to know that scaling itself is going to drag your efficiency down to the gutter. Otherwise, the manufacturer would have covered those copper tubes in the heat exchanger with calcium deposits at the factory.**

I'm sure moto has his reasons for saying what he did and maybe we misunderstood.

Some models never perform above 80% after the very first descale a less and less each time. This person came in here asking for help. I’m a licensed plumber and a tankless water heater expert but you took a science class**

 

[Noname.sixpack]

Trust the science ********

 

[1msucub]

Some models never perform above 80% after the very first descale a less and less each time. This person came in here asking for help. I’m a licensed plumber and a tankless water heater expert but you took a science class**

Moto, the reason I asked is that I've got a Rheem natural gas heater (10 years old) that has started throwing error code 13. Everything I've looked up said it was a ventilation or flame rod issue. You wouldn't expect scaling to be a factor in this, then? I've never flushed it, never had a problem, and output is fine.

 

[PooPopsBaldHead]

Is the removal of the scale doing damage or something? I have one in my rental house that is on a private well with really hard water and everyone in the neighborhood plus the builder recommends getting it descaled annually.

I will defer to your experience, but you should put an article out there. Every single manufacturer, plumber, and engineer seem to recommend it. I mean you can joke about the science, but calcium carbonate is nowhere near as good of a thermal conductor as copper. 100 times less conductive in fact. As that scale builds you are going to lose massive amounts of efficiency. .05" of scaling leads to 50% loss in efficiency according to this article.

https://www.awt.org/resources/seed-program/water-careers/science-of-scaling/

I am not trying to fight here. But if I am going to screw the pooch by descaling my tankless, I would like to know a little more on the "why". Are you measuring the efficiency before descaling vs after? I mean if it goes from 60% to 80% that's a win, right?

 

[Trojanbulldog19]

Just because some is experienced and certified doesn't mean they are the trusted expert on the topic. Most plumbers I've talked to and manufacturers say to descale the water heater.

I'm not saying moto is wrong I'm just saying he isn't the only school of thought either. I know a lot of certified and professional engineers that talk out of their *** and are wrong a lot or state their theories based on experience when there are a lot of others that say do something else.

 

[grinningmule]

Is the removal of the scale doing damage or something? I have one in my rental house that is on a private well with really hard water and everyone in the neighborhood plus the builder recommends getting it descaled annually.

I will defer to your experience, but you should put an article out there. Every single manufacturer, plumber, and engineer seem to recommend it. I mean you can joke about the science, but calcium carbonate is nowhere near as good of a thermal conductor as copper. 100 times less conductive in fact. As that scale builds you are going to lose massive amounts of efficiency. .05" of scaling leads to 50% loss in efficiency according to this article.

https://www.awt.org/resources/seed-program/water-careers/science-of-scaling/

I am not trying to fight here. But if I am going to screw the pooch by descaling my tankless, I would like to know a little more on the "why". Are you measuring the efficiency before descaling vs after? I mean if it goes from 60% to 80% that's a win, right?

Use hard tap water in a countertop food steamer and you'll see quickly how much output is diminished by scale build up on the heating element versus how much better it is after descaling it. I'll lean toward annual or bi annual descaling in hard water areas in a tankless unit especially here out west.

 

[PooPopsBaldHead]

Yeah when I lived in Texas, we had some massive scaling issues with hard water. It's obviously bad where we are in that all the houses built after 2000 seem to have a water softner loop added standard.

My old house in San Antonio was the worst I had. Scaling clogged the screens in the sinks. One of my old customers in Texas has a popular youtube channel and opened up some various age tank water heaters. The amount of scale was wildly variable. The first comment to the video convinced me to never get a water softener.

 

[johnson86-1]

Some models never perform above 80% after the very first descale a less and less each time. This person came in here asking for help. I’m a licensed plumber and a tankless water heater expert but you took a science class**

You are saying the water volume output never gets above 80% of the original after the first descale? Or are you talking about the temperature transfer?

 

[DawgInThe256]

We found the fifth dentist ***

 

[Motodawg]

My phone number is (601)573-5872. I’ll gladly explain my point over phone but I’m having a hard time making it typing it here. Plumbers call me to ask me about tankless all the time so I’m not sure that’s a great reference whichever one of yall said that. It basically boils down to this, dont descale until you have to. If the problem isnt scale, dont descale. When the manufacturer tells me to descale, i do, but never before. I let it be their call. I charge 125 an hour to work on tankless and 150 an hour if you argued with me on this post***

 

[PooPopsBaldHead]

After looking at your website, I see I am just outside of your generous service radius. Otherwise, I'd lock you up for a full day to check out my tankless and then explain to me how in the 17 a p-trap works in my house without any plumbing vents to be found. It's a mystery man..


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[grinningmule]

After looking at your website, I see I am just outside of your generous service radius. Otherwise, I'd lock you up for a full day to check out my tankless and then explain to me how in the 17 a p-trap works in my house without any plumbing vents to be found. It's a mystery man..


View attachment 24414

Next time I'm in McCall I'll check out that no vent situation. I've seen some a few things in my lifetime, such as the condensate drain on the AC unit draining down into an open pipe with no p trap present. Yep, just an open ended pipe stubbed up allowing all that glorious sewer gas to be sucked up and generously distributed through the house.

 

[Motodawg]

After looking at your website, I see I am just outside of your generous service radius. Otherwise, I'd lock you up for a full day to check out my tankless and then explain to me how in the 17 a p-trap works in my house without any plumbing vents to be found. It's a mystery man..


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Buddy, you can still call and bounce anything off of me, anytime. Doesn’t matter how far or whether I’ll earn a dime off of it or not. I’d rather you call me and get good advice, than call some hack. I give this same offer to anybody on this board. No asterisks needed.