Constant water flow to tankless water heater - Water Heaters

Maybe water leak.
Turn off all taps and put ear against pipe.
Call for qualified service technician who can work on tankless computers that heat water... and call plumber for plumbing repairs ... these are not same thing.
Don't buy tankless. Fix any tankless problem, yourself, inexpensively, same day by replacing 1 part: the whole thing:
http://waterheatertimer.org/How-to-install-gas-water-heater.html
Gene

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

1) Check for crossover:
http://waterheatertimer.org/Crossover.html

2) Copy following link for Rheem Tankless resources including no-error-code:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

3) Add comment and say what you find.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Possible flow sensor issue. Check to see if your water pressure fluctuates a lot or is fairly steady. These units are sensitive to the pressure. take care.

1. COLD MIX, HEATER DEACTIVATES
   If inlet water temperature is over 70°F due to geographic location, water maybe very hot out of the tap. This requires a lot of cold water to be added with it in order to attain a useable hot water temperature. The addition of too much cold water will overpower hot water demand from the tankless water heater. This slows the flow within the tankless water heater, decreasing it below activation point, which shuts off the heater. The end result is nothing but cold water coming out of the outlet. See: TWH E2-04 Overcoming fluctuating temperatures [PDF].
2. FLUCTUATING WATER PRESSURE
   If the water pressure in the home is erratic and the water flow is not consistent while a tap is opened, then the temperature of hot water will fluctuate. The minimum water pressure for the home should be 30psi or greater. For people on well systems the minimum pressure range is 30-50psi. The use of a pressure reducing/regulating valve is an effective way to maintain constant water pressure to the water heater. Watts brand 25AUB- ¾" or N35B-¾" pressure reducing/regulating valves or equivalent is suggested.
3. CHANGING FLOW RATE
   Major changes in flow rate can adversely affect the output water temperature of the heater. Increases from one major fixture running to multiple fixtures running at one time can cause the temperature to fluctuate. Stay within the heater's specifications. See: TWH E2-03 Outlet temperature vs. flow rate [PDF].

From the Bosch website.

Good Luck,
Gary

This electric demand water heaters has one heater element. The flow switch turns it on. The thermostat cycles it on and off according to temperature. There is no medium.
You need to run the sink on hot while you take a shower. This kind of cancels out the savings on electricity.
Or get a higher flow shower head. Your screen on the shower head may be partially fouled.
Here is the brochure. It shows the flow rates for the different models.
http://www.stiebel-eltron-usa.com/sites/default/files/pdf/brochure-dhc.pdf

tankless water heaters are a great appliance with one small draw back they require a constant flow of water through them to maintain production of hot water if the water presure fluctuates they can cut out momentarily or if your water supply is less than great ie hard ,high iron,
sulpher ect.. then the heat exchanger can become plugged over time like say 5 years. Contamination of the flow sensor/presure switch could also be a culprit depending on how handy you are a through cleaning with a good kettle descaler will probably help.
Good Luck

This sounds like a common problem with tankless type water heaters. The modulating burner has a set Btu range it can operate within, a maximum and minimum. With very low flow rates and very low temperature rises, the burner has trouble maintaining a steady output temperature because the btu load drops below the heater's minimum input. Typically the machine will overheat the water beyond it's setpoint, the burner will cut out, and then re-ignite once the output temperature has dropped low enough.
The solution to stopping this behavior is to simply increase the water flow through the device (i.e. higher flowing fixture or larger pump). This type of problem is exaserbated with recirculation systems that bring a very high water temperature to the unit.
Higher end tankless brands have a lower minimum input btu and thus fewer problems with this.

It might be a question of inadequate flow. All tankless water heaters have a minimum flow rate that must be met, typically .5-.9 gpm, before the heater will operate. In the summer time the incoming ground water temperature is higher, causing you to mix more cold water and less hot water to get a lukewarm temperature. This can reduce your flow rate near or below the minimum flow rate.
Here's a test for you, try running running a sink while taking your next shower. If the hot water remains mostly constant throughout, then your problem is with flow at the showerhead. The flow at a shower head can be reduced by buildup of scale and sediment. Also all showerheads have a flow restrictor that limits flow to 2.5gpm (some even less). Removing the restrictor will increase the showerhead flow rate as well.
Also look for any error code displayed on the digital read out of the heater. Some heaters will flash on their burner indicate light as well.

The cold main water pressure is too low to maintain a constant flow. Make sure you have no other appliences on, or your not comprimised by the lowering of pressure

water temp setting should be appx 120, any higher heat exchanger trips on overload and you must reset each time..