Tankless Water Heater Repair Advice: this article explains concerns, problems, & special characteristics of tankless water heaters, also called instant water heaters or "on demand" water heaters.
Page top sketch of a point of use tankless water heater courtesy of Carson Dunlop Associates.
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Conventional water heaters are relatively inexpensive due to their simplicity while tankless water heaters are more expensive to purchase and install. In 2009 in Toronto, Ontario a high capacity instantaneous water heater installation could cost $4000. CDN.
Their complexity also means that maintenance and repairs can be more expensive. Dedicated isolating valves help simplify draining and other regular maintenance.
The water heater must have a continuous fuel supply. Malfunctioning burners, sensors or controls will cause poor operation or may result in the system not working at all, meaning no hot water.
The small diameter of the heat exchangers means that these units are susceptible to clogging with scale, especially in areas with hard water. In hard water areas, annual de-scaling is recommended.
As with tank-type water heaters, some manufacturers recommend regular flushing - a step that removes sediment and debris from the heater, not scale.
If the heater is equipped with a water filter, usually an in-line screen that can be removed, inspected, and cleaned. The demand water heater filter screen should be checked and cleaned monthly, or performance will suffer.
Consumer Reports reports that some tankless water heaters do not heat continuously and constantly. If a particular model has this problem users will find that in the shower the water runs in cold bursts from time to time.
Watch out: In our own tankless water heater installation experience in the U.S. & Mexico we have confirmed that there can be hot water constancy & flow regulation problems, particularly in low-pressure tankless water heater installations.
See TANKLESS WATER HEATER INSTALLATION
Depending on exactly how hot and cold water pipes are routed to the tankless water heater and to various plumbing fixtures in a building, low pressure tankless water heater units are sensitive to reductions in water flow rate when additional plumbing fixtures are in operation in the same building.
The result can be complete cessation of hot water (the heater turns off on a too-low-flow-rate condition) or difficulty balancing the proper hot water temperature by attempts to mix cold water in at the shower or sink where hot water is in use.
We suspect that for this reason, after about 2004, Bosch stopped selling low pressure tankless water heaters in the U.S. However as recently as in 2012 these units continue to be sold and installed in other countries including Mexico where some homes depend on low water pressure delivered from a (not very high) rooftop water storage tank.
These low water pressure problems can be addressed by
Depending on how you use your demand hot water heater, an unpleasant jolt of cold water often occurs when water is turned on and off fairly quickly. This can happen at a kitchen sink when rinsing dishes or at the bathroom basin while washing and shaving, for example.
Rinnai™, a maker of tankless water heaters explains the cold water sandwich effect as follows:
"The term “cold water sandwich effect” is a term that is used to describe the introduction of cold water into the hot water supply line during frequent on/off operation of an instantaneous water heater. The cold water sandwich effect, when present, appears as a momentary drop in hot water temperature as it is discharged from a hot water supply outlet (i.e. shower, tub, or faucet). This phenomenon is present in the operation of all instantaneous, tankless style, water heaters, but is minimized with the high tech design of Rinnai water heaters.
The technology built into the Rinnai water heaters is designed to minimize the cold water sandwich effect. Rinnai water heaters are microprocessor controlled and when water flow through them ceases, they remain in a “ready to fire state” for approximately 1 minute. If water flow through a Rinnai water heater begins within the first minute following water flow stoppage, the water heater will fire back up within 1 to 2 seconds.
This minimizes the cold water sandwich effect that would otherwise be experienced with a low tech tankless water heater. It should be noted that the cold water sandwich effect cannot be removed completely from tankless style water heaters. The safety standards developed to insure the safe operation of water heaters require a delay in the ignition sequence of all gas water heaters.
While the cold water sandwich effect cannot be completely eliminated from standard plumbing systems, it can be eliminated from plumbing systems that have a supply and return hot water circulating system. Rinnai has developed 2 methods to eliminate the cold water sandwich effect in residential hot water circulating systems.
The first (and preferred) method to remove the cold water sandwich from circulating systems utilizes a small electric tank water heater (powered up) that is used with a dual purpose. The small water heater acts as a mixing tank to eliminate the cold water sandwich effect from the Rinnai water heater and it uses its electric heating element to offset the heat losses from the hot water circulating system.
The second method to remove the cold water sandwich from circulating systems utilizes a small 2 to 6 gallon storage tank installed on the hot water outlet of the Rinnai water heater. This tank acts as a mixing tank to blend the cold water sandwich with hot water and eliminating its effect at fixtures."
The hot water flow rate is not only dependent on the heating capacity of the water heater and the output water temperature, but also on the inlet water temperature.
Homes in northern climates draw water from colder water supplies, and since it takes longer to heat up colder water, tankless water heaters installed in these homes will have lower hot water flow rates. The design temperatures for many water heaters is 60 deg. F. but in northern climates (Toronto, Ontario, or Two Harbors MN), the incoming water temperature may be 50 deg. F. or even as low as 40 deg. f.
Portions of this article were provided courtesy of Carson Dunlop - that text has been edited and may not entirely reflect CD's views.
Continue reading at TANKLESS WATER HEATER SIZE REQUIREMENTS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
Or see ALTERNATIVE HOT WATER SOURCES to distinguish among these types of hot water producing systems.
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(June 28, 2014) Jenny kim said:
Hi, my name is jenny and i got burst pipe last winter with tankless heater.
I was out and the temperature was 30-28 degree in my area walnut creek california at that time.
When I came home, i found hor water pipe got burst on my roof and i got all waterdamage in every single room.
It was disaster. I contacted to insurance company, and company said, they won' t pay because pipe got frozen.
I have a question about tankless heater.
Hot water pipe is always keeping hot water inside with tankless water pipe?
How my tankless water hot water pipe got burst? Not cold water pipe burst before?
Because my hot water pipe got burst, so my house became sauna like three days.
I want to prove that my hot pipe just simply got burst because of pipe problem, not frozen.
Is any way that i can prove this tankless heater keep always hot water inside of hot water pipe?
Any one can help me? I got more than one hundred thousand damage, but insurance companh denied to pay it.
I will really appreciate it if anyone can give me advice, thanks!
I'm sorry about the terrible water damage you describe.
Tankless heaters are normally "off" - they do NOT keep anything hot. The design of tankless heaters causes a burner to turn on when water begins to flow through the heater. So no honest expert is likely to be able to help you prove that a heater was working in a what that it does not. Of course you may have some other type of equipment installed that I don't understand from just your comment.
You will want to take at least these two steps:
1. review your insurance policy details with an expert, perhaps an attorney, to be sure you understand what coverage you actually purchased.
2. While I don't encourage people ever to rush into a dispute, you may need assistance from an independent insurance adjuster who can negotiate with your insurance company on your behalf. The advantage is that such a person is expert on insurance policy coverage, laws, and in negotiation with the insurance company. The disadvantage is that the moment you consult an attorney or independent adjuster who is working for you, the relationship with your insurance company becomes adversarial. On the other hand, if the insurance company is stonewalling you AND if you believe you were entitled to inurance coverage, you may have no alternative.
(Aug 12, 2014) Anonymous said:
looking for anyone with a problem with nortiz tankless hotawter freeze ups
(Oct 7, 2014) Ed Deane said:
No reading from Temperature Controller - front panel. There have been power outages in the area. Getting cold water - luke warm in shower but no hot water.
What is the problem. I went through my gas provider for the install - their energy conservation program. They used a local outfit to install.
I noticed something else - usually HEAR
Ed does the unit have power?
I assume so. The fuse box shows no amp fuse being out.
Usually as I said - I usually hear the unit working - it's positioned in the garage - when my wife is upstairs running the water - the unit goes through it's operating cycle. That's not occurring.
Also, no reading from the Temperature Controller - front panel.
How would I know otherwise if NO POWER TO UNIT.
Check the power circuit with a VOM or if it uses batteries, replace them with known good ones.
Listen for the igniters as well as checking the display.
(Aug 16, 2015) Rick said:
My water heater tries to ignite when not in use. can't figure out why.
If a conventional water heater ignites only rarely it may simply be keeping the water at the temperature set on the heater's thermostat.
If a tankless heater is igniting there is a problem with a flow sensor, control, or there is water running somewhere that you haven't found.
The water heater burner should ignite when
- the heater is in use and temperatures drop due to incoming cold water into the heater
- the heater has not been in use for many hours and has cooled down enough to turn on the burner
A bad thermostatic control could also be at fault.
WATCH OUT: if the burner is not turning off when the heater reaches the cut-out or high temperature the system is unsafe, could explode and kill someone, and should be left off.
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