I have a Bosch 125x NG. I have spark at pilot, good water pressure took apart pilot tube at gas valve no gas loosened screw on pilot electrovalve there is gas unit will not fire

Check pilot is clean and strong Also check sensor is clean and connections are clean and tight .

Tankless?... call service technician

Tank? clean arrestor screen, replace gas valve thermostat
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html

http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent

Gene

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

I have the same machine first they said replace the micro switch i did then rebuild the water valve did not enough gas presure had it checked revented the unit the unit is brandnew relubed the water valve idk

Your thermo couple is bad. Thats the copper tube that goes from the gas valve to the pilot. It senses thats the pilot is lit. Thats not working thats why it goes out. You can get a new one at lowes or home depot for about ten bucks its pretty easy to change just dont kink it when you put it in. It will just plug in at the pilot and screw in at at gas valve.

Having the same problem with mine. Looking for a replacement generator. Seems that if your water pressure or flow is not adaquate your will have this problem. Get worse over time. I took mine apart and it got better then started doing the same thing again. I turn on several faucets to overcome problem. Still it not good. The 1600H does not appear in the Bosch website parts list models. They do say that a third party does the fulfillment in the notes at bottom on other units...maybe call them

You have to fix this leak around the water valve before
it causes damage to your equipment.
1. Close the water supply valve going to your tankless
water heater.
2. Unplug or close the natural gas valve.
3. Now, you can work fixing the leak.
4. Once completed, you can proceed to open the
natural gas valve as well as the water supply valve.
5. Then, have it tested to get it done.

5.

sounds like blockage pilot jet nipple needs cleaned best of luck

The incorporation of an anti-back flow, flue pipe insert may be your solution, also the pilot flame control may need to be adjusted up a little.

Good luck
Aduz

I found that the solution to my issue of not igniting was due to a bad pilot electrovalve part #8708501249. It was about a $50 part that was bad from the start.
Really disappointing that Bosch's QA would let a such a defective part ship. I spent about 3 years of using a workaround with a fan blowing air to get ignition until it finally failed. I had a tech look over the system to point me in the right direction.

The clicking is a good sign. What are you trying that not working? How is the water flow-is it strong? 1) Turn the flow control button all the way to your left - this will increase the flow.
2) Pull the relief valve to simulate water flow and listen for clicking sound, and hopefully, main burner ignition. ( if installed in basement or kindly use bucket to catch water) The 1600 H NG will automatically shut off firing after 5sec of clicking.
3) How is the venting-use a household digital carbon monoxoide detector to measure any backspill from chimney.
4) Was the gas line disconnected in anyway after heater was installed? Air in the gas line will cause the igniter to click but no gas to fired the main burner.

Todate i have installed 11 Bosch Tankless Heaters -- 9(125 NG) Which is the same as 1600 Series
1(1600H NG) and 1(1600P NG)
Guess which one I having problem with- You guess it, however, the problem is their electrical wiring.

BE CAREFUL IN CALLNG BOSCH TECH. FOR SUPPORT. THE ARE GRILLING YOU TO FIND A LOOPHOLE WITH YOUR INSTALLATION TO RELIEF THEMSELF OF THEIR WARRANTY.