Hi, I have the 1600 NG tankless water heater. Everything works great, but I installed low flow hot faucets throughout the house and now the igniter will not click on. It works for the washing machine. And I have turned up the "turn on" sensitivity all the way up. I have to turn on all of the faucets in the house to get the heater to turn on. Then it does not stay on when I turn them off one at a time. If I turn off and on the water quickly, it turns on; with all of the hot faucets in the house turned on. Help!!!!

The igniter may not be receiving the call for heat, im not familiar with these setups, but if there is sensor or a heating element they could have gone bad.

Replace single-handled faucet cartridge, and see if hot flows to that faucet again.
http://waterheatertimer.org/Crossover.html

Exposing tankless to hard water causes reduced efficiency within a few months, and can cause Total failure of parts within two years.
Do not expose tankless to more than 11 grains hard water.
Here is research pdf conducted by water softener industry comparing tankless andf tank-type:
http://waterheatertimer.org/pdf/Battelle_Final_Report.pdf

To solve problem long-long term, install tank-type gas water heater from local box store for $350.
http://waterheatertimer.org/How-to-install-gas-water-heater.html

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

All resets and breakers trip with high heat.
Do you mean the tankless unit is tripping the 40 amp circuit breaker?
Or the thermal cut-out, located on unit, is tripping?

Is this a new installation?
Or was the tankless working before and stop working?

Copy following link to check wiring.
AE 9.5 requires 40 amp breaker and 6 gauge wire.
http://waterheatertimer.org/How-to-wire-Tankless-electric-water-heater.html

If the unit is tripping the thermal cut, -out, then product manual says to call Bosch or service technician.
Call Bosch 866-330-2729
http://waterheatertimer.org/pdf/Bosch-Powerstar-AE3.4-7.2-9.5.pdf
Thermal cut-out can trip if water flow is too low.
Try changing power selector screw from Hi to Lo so only 1 element is ON. See diagram page 6 of manual.
Adjust the 'outlet service valve:' The manual recommends that a ball valve be installed between hot outlet and faucet. Adjust the valve so more water flows to faucet.
Remove aerator, clean aerator, don't use low flow restrictions or low flow shower heads, replace leaky faucet cartridge on single-handle faucet.

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

1) Guesses: Sounds like a bad single-handled faucet cartridge, or low water flow at faucet, or clogged water filter.
Replace faucet cartridge, clean the aerator, and/or clean sediment out of pipes below sink, and clean water filter at tankless unit each month.

2) For exact measure of problem:
Typical faucet can have 2 gallon per minute flow rate.
2 gpm flow rate means faucet fills 1 gallon container in 30 seconds. Test faucet using 1 gallon container and a cooking timer to get flow rate.
Clean aerator to improve flow rate. Compare kitchen flow rate with other faucets in home.
http://waterheatertimer.org/Low-hot-water-pressure.html

Most homes have 1/2" diameter pipe running to kitchen faucet.
100 feet of 1/2" diameter pipe holds 1.2 gallons of water. This assumes no sediment build-up inside pipes.
http://waterheatertimer.org/Water-heater-recirculation-system.html

Assuming only hot is turned on: If faucet is 100 feet away from water heater, and pipe diameter is unobstructed 1/2" diameter, and faucet has 2 gallon per minute water flow, then hot water should arrive in 36 seconds.
50 feet away, and hot water should arrive in 18 seconds.

If kitchen has single handled faucet, and the handle is raised in the middle, then equal amounts of hot and cold water are drawn at same time. This doubles amount of time for hot water to arrive.

If single handle faucet has a bad cartridge, then faucet can have crossover.
Crossover means that cold water can enter the faucet even if faucet is turned to hot.
Bad single-handled faucet cartridge can delay or stop the arrival of hot water.
http://waterheatertimer.org/Crossover.html

Tankless require maintenance including cleaning combustion parts yearly, de-lime heat exchanger frequently, and clean water filter each month.
http://waterheatertimer.org/pdf/Tankless-maintenance.pdf
http://waterheatertimer.org/pdf/Bosch_Overcoming_fluctuating_temps.pdf
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

Add a comment for more help.

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For a price, expert works with you while you work on water heater or any do-it-yourself project.
Fixya is always less expensive than a service call.

Since you have hot water at all the other fixtures, the problem lies in the sink, not the water heater. It could be that the sink is farther away from the water heater than the other fixtures. It would take longer to get hot water.

Before calling service technician, open following links for Bosch troubleshoot resources:
1) General resources:
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

2) Sales page: Notice the paradoxical promotion of unlimited hot water that saves 50% off utility bill.
http://www.boschhotwater.com/BoschHotWatercomHome/GasProducts/BoschModel1600H/FeaturesandSpecs/tabid/1024/Default.aspx

3) 1600H troubleshooting. Click each item and it opens drop down menu that also has links to service bulletins. Lots of reading, but a great way to get familiar with your product.
http://www.boschhotwater.com/HelpfulResources/TechnicalSupport/BoschAquaStarModels/1600HTechSupport/Troubleshoot/tabid/1094/Default.aspx

I do not recommend tankless for the number of difficult and expensive problems, the required yearly maintenance, plus the specific need for incoming air quality, sufficient quantity of gas, water quality, water pressure, water volume, and correct venting and drainage of vent condensation. And never recommend self-installation since most tankless manufacturers refer immediate problems back to the installer.

Assuming the tankless was installed correctly and not defective:
Other problems can be caused by household conditions.
For example crossover:
http://waterheatertimer.org/Crossover.html
Tight house: tankless require more incoming air than tank-type because they burn so much more fuel per minute of operation:
http://waterheatertimer.org/pdf/Bosch_Ventilating_tight_houses.pdf
http://waterheatertimer.org/pdf/Bosch_Overcoming_fluctuating_temps.pdf
Low water pressure:
http://waterheatertimer.org/Low-hot-water-pressure.html

Take a moment and vote on answer:
And take advantage of fixya expert assistance live.
For a price, expert works with you while you work on water heater or any do-it-yourself project.
Fixya is always less expensive than a service call.

Water heater is heating water but only luke warm water arrives at faucet.
Open TP valve and confirm that hot water is available.
If water at TP valve is hot, then problem might be plumbing-related, for example crossover.
http://waterheatertimer.org/Crossover.html

Before calling service technician, open following link for Rheem troubleshooting resources.
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

List of causes MIGHT include one of following:
Bad household circuit breaker that powers electronics, or loose wire inside outlet where tankless plugs in.
Tankless fuses and control board.
Water flow rate too low. Minimum .8 gallon required (depending on model)
Tankless inlet filter clogged.
Household aerators clogged at faucets.
Crossover at single-handled faucet
If installed, there can be crossover at mixing valve.
Faulty household check valve, including check valve on re-circulation system if that system is installed.
Restriction in household water line, such as clog at elbow.
Unequal pressure in household hot and cold lines, caused by restriction in hot line. When single-handled faucet turns on, the cold water pressure is higher so hot does not flow and tankless will not turn on.
Loose wire connection inside tankless.
Unit temperature set too high.
Unit temperature set too low.
Water temperature is very hot coming out of tap, so more cold is added, but that reduces amount of hot water flow, so tankless turns off because flow rate is too low.
On some tankless, if water is preheated by solar or other indirect source, the burner will not activate.
High mineral content in water > delime tankless yearly
Misaligned temperature sensor
Low gas pressure. Wrong type of gas. Undersized gas line.
Too many faucets on at same time.
Faulty tankless water valve. Water valve stuck.
Fluctuating household water pressure, for example MUD and PUD district water pressure problems or water well pressure.
Faulty household pressure reducing/regulating valve if installed.
Faulty household pressure tank, if installed -or- pressure tank needs to be installed.

The manual says to hold a match near the pilot while the ignitor is trying. It says that if the unit lights the pilot orifice may be dirty or clogged. Then the manual says to check the voltage on the igniter. It should be 1.3 volts DC minimum if it is not means the electronic control box is defective.

Let me know the status ...Kevin

You are doing everything you can. Your dishwasher probably isn't drawing enough hot water to activate the unit so opening the faucet and flowing more water will activate the unit. Just try to adjust the flow from the faucet to a point it, plus the draw from the dishwasher, will activate the unit. This will come with trial and error as I am sure you have already experienced. Also, open the dishwasher when it does get filled and check the water temperature. You might have the unit set at a low discharge temperature. Do you have a touchpad to control the water temperature adjustment?