1600 ng hydro. The Water control valve cracked due to heat loss in bldg. Can not find part or how to separate from rest of components.. Any ideas?

That voltage does not seem high enough. Supposed to be 1.6 VAC and I got 2.5 VAC. Do you have the water flow turned to the maximum? Is there something blocking water flow? The hydro voltage should be checked separetly from everything else, so if you can't get the VAC higher, my guess would be that's the problem.

I believe this is a hydro-sparker pilot ignition then burner on when T-Couple/Flame Sensor acknowledges pilot lit.
W/O the signal feedback the Gas Valve will not open and light burner.
This is a Technician Service Job as you have insufficient knowledge to DIY this potentially dangerous LP/NG Control Valve/Sparker Assembly
I assume that lack of knowledge by your lack of a Manual for the Unit
You cannot force ignition on a hydro-sparker manually.

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.

On a 1600H for god sakes give the Tech the S/N and the color code on the wiring at the flow sensor that starts the hydro sparker. They changed the thing in Mfr and there are 2 different parts. And also rebuild the water valve occasionally like every 3 years as Bosch recommends even if the cover which guides the pushrod is expensive. FYI we now usually buy a new WV as it\'s more reliable than rebuilding and you get all new parts. It\'s like $125 for a WV vs $59-71 for just the WV cover. Also never run these on very hard water fro a long time or you\'ll never descale em without Whitlam and a long wash out.

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

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

check filters and increase coldpressure

Aquastar 1600H NG Natural Gas Tankless Water Heater Bosch AquaStar Model 1600H NG Natural Gas Whole house tankless gas water heater, 117,000 Btu input, natural draft with hydro-generated ignition. Provides endless hot water for one major application at a time . Can replace 40-gallon storage tank water heater. Optional Accessory: Model AQ1- Power vent with built-in... More freeze protection when venting horizontally. Capacity: 1 to 2 Bathrooms Dimensions: 8.75D x 18.25 W x 29.75H Weight: 40 Max GPM @ 45F Rise: 4.2 Energy Factor: NG .80 LP .84 Minimum Input: 28,000 Maximum Input: 117,000 Vent Size: 5 Gas Connection: 3/4 Water Connections: 1/2 Warranty: 12-year warranty on heat exchanger, 2-year on parts Features: Endless hot water Can save up to 50% off utility costs annually Perfect for one major application at a time No standing pilot, hydro generated

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.

I found the manufactures website and read this specific tech bulletin. I will be replacing or repairing my water value soon.

http://www.boschhotwater.com/Portals/7/TechBulletins/TWH-G1-25_Water_valve_rebuild_B.pdf

The bulletin said the following:
If the burners fail to go off immediately when the
water is turned off, usually due to mineralization in
the water valve on older heaters. To test for this
possiblilty, run hot water at a faucet, then shut off
the cold inlet supply and observe if the burners go
off immediately. If they do not the Aquastar will
overheat and shut down on safety depending on
the delay.