Clogged tankless coils:
Here we explain how to correct clogging at the tankless coil in order to improve the hot water pressure, quantity, flow from a tankless coil used for making domestic hot water.
We include a simple diagnostic procedure to find out if your bad hot water pressure is due to clogging in the hot water piping or in the tankless coil itself.
Page top photo: We found this pile of abandoned tankless coils at a home where the owners complained of frequent loss of hot water pressure or flow rate. Mineral clogging was blocking hot water flow, but the repair person simply replaced the coil over and over without explaining the cause: water high in mineral content. The owners needed to install a water softener.
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Hot Water Heater Tank Clogging Diagnosis & Repair - Tankless Coil De-Liming Procedure Details
[Click to enlarge any image]
Before starting on a project to de-clog or de-scale building water supply piping, let's be sure that we are solving the right problem by making a reliable hot water pressure or both hot and cold water pressure diagnosis.
Clogged hot water supply piping:
Water supply pipes may be clogged at the water heater or at other locations, from minerals, soil, or other debris.
and WATER HEATER SCALE DE-LIMING PROCEDURE for diagnosis and repair procedures.
Corrosion, debris, dip tube or anode problems in the water tank:
Accumulated debris in a water heater, and debris from a corroded or disintegrating hot water tank dip tube or hot water tank sacrificial anode can also block the hot water outlet opening, resulting in low hot water pressure in a building.
See ANODES & DIP TUBES on WATER HEATERS
Hot water pressure and hot water flow in a building may be poor even where a mixing valve has been installed. This condition could be due to poor overall building water pressure or due to clogged pipes.
If cold water pressure is good and hot water pressure is poor,
the problem is not an overall building water pressure issue. There is a problem with the hot water system that needs to be found and corrected.
If hot water pressure is strong when the water is first turned on but flow quickly falls off
to a weak hot water stream, it's likely that the hot water piping (or tankless coil) are clogged.
Often this repair involves using acid to try to remove minerals that are clogging hot water system piping or a tankless coil, or the tankless coil may need replacement.
Abandoning a tankless coil altogether:
When we bought our house the tankless coil was almost totally clogged with minerals, and we figured that it wouldn't provide enough hot water anyway, so we abandoned it. In the photo at left you can see the round black tankless coil face, with two holes - where we removed the cold-water-in and hot-water-out pipes and simply abandoned the tankless coil.
A separate water heater was installed in our utility area. (We'd have preferred an indirect-fired water heater which is discussed later in this article but that's not what we got.)
For more detailed help in diagnosing the cause of poor water pressure or flow rate due to clogged pipes or clogged tankless coil
Given first, just below, is the general procedure for using an acid flush to clear clogged water pipes or tankless coils.
Some plumbers will attempt to clean out water supply piping that has become mineral-clogged.
Photo: lime scale fragments collected from a water heater. Similar hard limescale forms inside of hot water pipes and particularly in tankless coils used to produce domestic hot water.
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Often an acid flush will indeed restore or improve water pressure and flow through previously-clogged building piping. But the process has these limitations:
Krappe described using an acid-resistant pump and tubing connected to fittings to circulate an acid-wash through scale-clogged copper piping back in 1940.
Plumbers still use this method today. The apparatus must be designed to let the scale particles and gases escape. Plumbers may simply use an acid-proof pony pump and fittings to cycle the acid wash using a plastic bucket as the rec
eiving sump.
Watch out: this is a dangerous procedure risking acid burns or other hazards. Don't try this procedure if you are not trained and equipped to do so.
But we have been informed by some plumbers that using acids to clean a tankless coil leave the coil internal surfaces etched and that the result can be faster scale formation than previously
See TANKLESS COILS for an explanation of how these water heaters work and why they clog up and how to stop clogging up the coil.
See WATER PIPE CLOG REPAIR for a discussion of loss of water pressure due to clogged piping or clogged tankless coils.
At LARGER DIAMETER WATER SUPPLY PIPES we discuss the benefits of using larger diameter water supply piping both to improve water pressure and flow and also to delay the clogging of pipes due to minerals or rust.
We received this un-solicited promotional information from Worp in October 2020. The company says that their portable de-scaling mahine uses a combination of compressed air and a pump to "strip off" mineral scale from the interior of almost any device: hot water pipes, tankless coils, water heaters, industrial equipment. Following their air treatment HCL (Hydrochloric acid) cleaner is used as a final step.
The briefcase device is the pulse generator, and you'll notice that the de-scaling system requires a separate source of compressed air.
We would like to see field reports from people who've tried this system.
Your information on how to remove scale in a tankless coil to improve hot water pressure and flow led to me doing this task myself. I am very mechanically inclined and rather technologically proficient but I still wanted to get an understanding of the processes.
I had a pump that would do the job but I was concerned about using an acid, even diluted.
I turned off the valves separating the tankless coil in my Burnham oil burner and luckily had tees in place already. All I had to do was get fittings for the garden hose adapters and screw them in place, I then connected the hoses to the pump and one to drain freely into my 5 gallon pail filled with about 2 gallons of water.
I then added a 28 ounce container of Lime-A-Way and started pumping. The water was nearly non-existent when I started and the pumps thermal overload went off giving me a break.
I did this pump on-thermal off routine about three times, each time letting the solution sit in the tankless coils for approximately a half hour. I was getting almost no improvement. I then decided to reverse the flow thinking what could be the harm.
The pump started and the bursts of gray water were getting more and more frequent. After three more thermal overloads I was running freely. Success is at hand!
But wait! All this bragging of success has its downside. As best as I can remember this issue isn't covered anywhere on your site.
What I found is that after the water flow had returned to normal I still had low flow after a few bursts in my faucets upstairs. I then removed the aerators and strainers from the faucets and all flow had finally returned!
It might be a good idea to add a step to your water pipe or tankless coil de-liming or de-scaling process to remove the strainers and aerators from their faucets before turning them all on to rinse the tankless coil and system.
[See WATER PIPE CLOG DIAGNOSIS
and WATER PIPE CLOG REPAIR for details about diagnosing and clearing clogs in pipes, faucet strainers, and plumbing valves, including debris flushing - Ed.]
Bernie Daraz, Newtown, CT
Watch out: using Lime-A-Way, EasyPaks®, or Jelmar CLR® ("stain removing" cleaners designed to remove rust, calcium or lime) and similar cleaners to remove the white mineral crust on exposed metal surfaces such as a stainless steel kitchen sink can leave a black stain that is difficult to remove.
If you already have this problem, try using a nonabrasive cleaner designed for cleaning stainless steel surfaces, such as ScotchBrite™.
See WATER HEATER SCALE PREVENTION
...
Below you will find questions and answers previously posted on this page at its page bottom reader comment box.
What's a typical lifespan for a coil? I am having a problem at a Holby mixing valve.
Holby says it's not the valve but a flow problem with the hot water source — too big a difference in pressure between hot and cold sides.
My plumber says it's not the (19 year old coil).
The valve works at low flow but has a temperature drop when the demand for water increases. In directions the coil is clogged up but my plumber insists it's not the coil. Amy ideas? - On 2022-11-28 by Bob-
Reply by InspectApedia (Editor) (mod) - lifespan of a tankless coil for hot water production
@Bob,
A tankless hot water coil can clog, and reduce flow in just a few years, or it may last decades.
The determinants are
The rate and volume of hot water used - more hot water used = more scale accumlation at a faster rate
The hardness (level of mineral content) of the water - harder water = higher mineral content = more scale accumlation at a faster rate
The operating temperature of the heating boiler - higher operating temperatures - more scale accumlation at a faster rate
A big difference between hot and cold pressures when it's the hot water flow rate that is much less than cold, will often point to a clogged tankless coil.
If that condition developed slowly over time, it's even more likely.When the hot water temperature falls more than it used-to the problem could be a partly-clogged tankless coil, lower boiler temperature, or part-clogging in the Holby tempering valve.
I am inclined to respect the Holby engineer's opinion, but you might want to also see
HOLBY TEMPERING VALVE INSTRUCTIONS [PDF]
I see rusty water coming from hot water in bathtub that is never used. Also from another sink. All found during home inspection.
We have found nothing.Inspector suggested could be a issue w/heating coil. We think it is from non use. Acid wash? Suggestions? - (Apr 29, 2014) john popa
Reply: NO. First check for corroding galvanized iron piping
John,
Don't do anything yet.
If the home has galvanized iron pipes and water sat in piping without flowing for some time, rusty water would be no surprise and should flush out with use.
An acid wash has other risks including toxicity - not something to undertake lightly.
And tankless coil tubing is copper, not likely to be a source of red rusty water.
As long as you are not seeing the same discoloration elsewhere, the unused pipe theory holds water.
I took this photo of reddish brown water running into a bath tub
waterbrown.jpg
under just the same conditions as you describe.
There may be other implications: galvanized pipes in an older home mean new piping is in your future.
After municipal stoppage of water to our home we are unable to get any hot. water flow from our geyser even though the cold water tap is fine
Can you assist with a solution ? (June 6, 2014) Anonymous
Reply:
Are you seeing no water flow at all or water flows but is not at all hot?
If the former look for a debris-clogged valve or pipe elbow and try flushing the piping system
If the latter the problem is with the geyser itself not the water stoppage
My 36 year old house has an indirect hot water cylinder that I suspect contains a huge amount of limescale, as I live in area with very hard water! Due to size of the airing cupboard, I'd guess the plumbing problems would be huge, as there is very little room to get at the pipework surrounding the cylinder?
I can figure out how to dissolve the limescale OK, but as the hot water flows out of the cylinder at the top, I'd guess that any solid residues will stay in the cylinder, due to gravity? I might remove the immersion heater and work through the hole somehow?
Am I going to run into problems afterwards, if I use chemicals here and it might thereafter build up again quite quickly? Perhaps I should consider a follow-on yearly descale, to keep on top of it afterwards? Being a pensioner, I don't have the funds, to get a new cylinder fitted! (Aug 15, 2014) D. Laws. Near Bedford
Reply: clogging occurs in tankless coils more than in indirect water heaeter coils: what's the difference?
D.L.
You're correct that scale or lime will tpically remain in and on the bottom of the hot water cylinder. We've removed such scale by removing the heater's bottom drain, draining out all of the water, and then GENTLY probing and breaking up loose scale into fragments that would flow out through the drain opening. We then flushed the heater by briefly sending bursts of cold water in at the heater inlet.
If scale is absolutely solid on a hot water cylinder interior surface, only by using a de-scaling agent are we likely to get that out. If you use chemicals you'll want to be sure the cylinder is very thoroughly flushed to avoid drinking or bathing in something harmful.
Once cleaning the cylinder, (for U.S. & Canadian readers - a hot water tank) the most effective long term fix for hard water high in mineral content is to install a water softener. You may hesitate at that expense, but consider that a longer-lasting solution is likely to be less costly and less disruptive than ruining the building piping and heater with scale.
Really? It's unusal to find scale in the heating coil used in an indirect water heater because the water circulating inside the coil and loop of piping should be water from the interior of the heating boiler itself. That water normally remains fixed - the same water is being re-used over and over.
Where we expect scale in water heating equipment is where new water is constantly running through the heating coil since that new water becomes a source of minerals that over time are deposited on the hot surfaces of the coil. So a conventional tankless coil gets scale clogging - house water runs through the coil, cold-in and hot-out. But the coil inside of an indirect water heater is using boiler-water and ought not become scale clogged.
SO let's be sure which type of hot water supply we're discussing. Compare
The way hot water is being made between
- TANKLESS COILS - house water runs through a coil immersed inside the heating boiler
and
- INDIRECT FIRED WATER HEATERS - boiler water runs through a heatingcoil immersed inside the indirect water heater tank
I have had to replace my heating coil, for my hot water, on my oil furnace 3 times in the last 3 years. It is now at a point where my hot water again is just trickling, I'm assuming due to the coil being clogged again. The heating coil on there was just replaced about a year ago. This is getting extremely costly and I want to know how I can fix this problem once and for all?
In reference to my question below, the house is only about 8-9 years old and went unoccupied for 2 of those years. - 5 Feb 2015 Robin
Reply:
Robin:
I would first have the water tested for hardness and for aggressiveness or corrosivity. Based on those results you may want to install a water treatment system to process all of your home's incoming water to avoid these problems.
An alternative worth considering is to abandon the tankless coil approach to making hot water completely by installing a separate water heater. An option to consider is the installation of an indirect-fired water heater. See
How long should I pump acid through my hot water coil after full flow has begun? - On 2015-11-18 by zeke
Reply by danjoefriedman (mod) - acid pumping time for successful scale removal?
Zeke I don't know of an objective acid pumping time criteria but I figure when I stop seeing new chunks of mineral debris and silt leaving the coil and when water runs freely (as you said it is) then it's time to stop.
...
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