20 Most Recent Bosch 1600H-NG Natural Gas AquaStar AquaStar Natural Gas Tankless Water Heater... Questions & Answers

If there is not a clicking sound, it almost always means the main ignition or control unit (box with red and green lights and wires coming from it) is not getting the supply voltage. The voltage is supplied by a generator that is getting energy from the flow of water (the "hydro generator"). First disconnect the wire connector at the hydogenerator and check the voltage while water is running. The manual says you should read 1.6 VAC (I read 2.5 VAC). Make sure your voltage reader is on AC, not DC. If you have at least something like 1 VAC, then the next thing to check is the "microswitch" that allows the hydro generator voltage to reach the ignition unit. To check it, disconnect the other wire connector that is on the black wire coming from the hydrogenerator that is closer to the ignition unit. Then with the water running, stick a small screwdriver in the male plug side to short the two wires in order to bypass the microswitch (per Bosch tech support instructions). You should now here clicking and see the unit work. This is what happened with me and tech support said I needed to order a new microswitch and gave me a part number and telephone. But don't stop reading here. You can see the microswitch when looking up at the underneath of the unit. It's a small white 1x1 inch box-like shape held by 1 screw. After removing it, I noticed the microswitch had a removable cover (which is strange for a switch) and opened it to discover the internal switch can actually move inside because it "automatically adjusts" itself when it is first put in (it stays more firmly, but not rigidly in place when the cover is on). So you can mess up when putting it in. Don't bump it. It can easily get out of its working range of motion, which is why mine stopped working: it was a bad design to use this type switch in this application. So I slide the internal switch back close to the spring side ("default" position), put the cover back on, carefulyl screwed it in place, and now it works.

The purpose of the mechanical microswitch is to not allow the hydroenerator voltage to the ignition unit unless the "pushrod" has opened the main gas supply. It prevents clicking if there is no supply gas, so it is not needed (you can electrically bypass it with a splice) if everything else is working fine. But don't blame me if you do this and for some reason it ruins the more expensive ignition unit. The microswitch is turned on by the pushrod when the pushrod leaves it's default position. The the pushrod moves only about 2 to 3 mm when you turn on the water. You can see the pushrod when you unscrew the microswitch, and you can watch it move. The problem is that the microswitch mounting is not precise enough for the small pushrod movement and the pushrod's default position can change with age of the diaphragm or change in the grease. So their automatically adjusting microswitch that makes up for lack of precision in design and pushrod movement can stop working when the pushrod changes position. My unit was 2 years old.

Bosch 1600H-NG... | Answered 3 days ago

If you can't hear clicks, then very likely it is the "microswitch" that is a rectangular white plastic box that can be seen at the bottom of the unit from underneath. It's purpose is this: when there is gas pressure, a pushrod turns the switch on, thereby allowing electrical current to flow from the "hydrogenerator" to the igniter unit. The hydrogenerator generators from about 1 to 2.5 volts AC (not DC) when water is flowing, powering the generator which powers the igniter unit....assuming the microswitch is allowing electrical current (the voltage) to pass through. It is a "self-adjusting" switch because the pushrod can come out at different pressures. So if your gas fluctuates, the microswitch will be fixed to a higher pressure level, but not be able to turn on if the pressure drops. This is because the pushrod is not pushing as far. It's simple to unscrew the plastic box and push the teethed switch setting back to the initial default position, and then carefully replace the plastic cover. Then do it again next time it stops working, a year or two it seems for many people. You can take out the switch and connect it's two wires directly, but if there is no gas pressure and you let water flow through, the igniter unit will constantly be sparking and thereby might fail early. If there is no gas pressure, then maybe it is because of a local leak and thereby bypassing the switch is a built-in explosion hazard, but that would require the sparking to no longer be internal to the ignition unit.

Bosch 1600H-NG... | Answered 3 days ago

Any time you bypass any type of regulator you risk putting everyone in the household in danger. For one, you cannot control the temperature of the water which, anything that is over 130*F (54*C) will cause scolding and blisters within just a couple of seconds.
Second, if there is no regulator then how will the unit know when to turn off the gas so it doesn't boil the water? I would be concerned with potential gas leaks and over-heating which can cause the water heater to explode.

I would have someone else come out and replace the limiter. Bypassing is a temporary fix to a more permanent problem.

Hope this helps.

Bosch 1600H-NG... | Answered on Mar 30, 2016

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.


Bosch 1600H-NG... | Answered on Jan 25, 2016

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.

Bosch 1600H-NG... | Answered on Nov 20, 2014

When you do not hear clicking the first thing to check is to the check the microswitch. See my answer on this question: http://www.fixya.com/support/t9769963-bosch_model

Bosch 1600H-NG... | Answered on Nov 19, 2014

No, its correct. Its just labeled incorrectly in the manual. The Bushing should be pushed up all the way(use dish soap to lubricate that oring) and the clip installs on the bottom of the bushing.

Bosch 1600H-NG... | Answered on May 06, 2014

Bosch 1600H NG??? I suppose. If so you need a digital manometer.
Take a static (off) reading then leave it hooked up and start flow. Watch pressure draw down and you should see the heater draw Water Column down below 5" as the pocket of NG in the pipe just before the unit draws down to minimal to keep heater lite. In that case problem in gas line size/gas line run length, Meter pressure.
If you have and maintain in operation 5" WC then is probably the water valve needs rebuilt along with a new diaphgram and also the water filter should be replaced too. This occurs esp after 2-3 year as Bosch specs rebuild at 3 yrs on the Maint Schedule. Also clean all the faucet aerators for good flow above 1.25 GPM Min at all faucets.
Under a single faucet flow (laundry sink) of 2.25 GPM the flame bed of the Unit should be 1"+ high and uniformly Blue.
I assume at this time you either have a Maint problem or you could be overflowing the heater's Winter capacity. This unit @ 70F rise only makes about 2.2 GPM. It's strictly a single use faucet heater at 117,000 BTU.
When you do the Maint look to see if there is corrosion between the GV pushrod and the water valve pushrod. Notice there is a huge mis- match in the 2 rods sizes.These units occasionally (more the 125B) corrode there and the GV will seize on and boil the heater dry and open a seam so you really want to maintain it to Bosch Specs and Schedule.
Note: This is a gas appliance & requires skill and knowledge to service. While Bosch may say you can DIY, I'd readily advise a Bosch approved Service Tech or Plumber do any rebuild. The Digital Manometer alone is a $100-150.00 item and it's the ONLY way to get accurate gas pressure readings.

Bosch 1600H-NG... | Answered on Mar 15, 2014

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.

Bosch 1600H-NG... | Answered on Nov 10, 2013

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.

Bosch 1600H-NG... | Answered on Dec 23, 2012

replace it with the same thing but newer

Bosch 1600H-NG... | Answered on Nov 02, 2011

You mentioned that you already check the gas pressure...so it should not be a low gas pressure issue, but make sure that you also check it with the burner running to make sure it is not dropping gas pressure when firing...
The other thing that I would check is water pressure and water flow...
If you are running a higher pressure on the water and the water flows through quicker then the water will not get as hot...in fact some of the very first units like this, did not adjust flame, but they changed temperature by regulating water flow...backing the intake side water valve off a bit can make a big difference is water temperatures...many units also come with flow restrictors to eliminate this problem...

Comment back if you have more questions...


Bosch 1600H-NG... | Answered on Sep 18, 2011

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.

Bosch 1600H-NG... | Answered on Aug 29, 2011

Before calling service technician, open following links for Bosch troubleshoot resources:
1) General resources:

2) Sales page: Notice the paradoxical promotion of unlimited hot water that saves 50% off utility bill.

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.

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:
Tight house: tankless require more incoming air than tank-type because they burn so much more fuel per minute of operation:
Low water pressure:

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.

Bosch 1600H-NG... | Answered on Aug 28, 2011

Are you asking about tankless gas or tankless electric?

You posted under Tankless gas water heater: gas type tankless plugs into standard 120Volt household outlet to power circuit board. You need larger gas line than used for tank-type gas water heater.

If you are asking about volt and amp draw of Tankless electric, then that depends on specific model number.
For example, if each tankless element draws 3500Watts, and unit has 3 elements, you will need 3 additional 20 amp 240Volt circuit breakers. Volts x amps = watts. 3500 watts divided by 240Volts = 14.58 amps. At full blast, this unit would draw 43.75 amps and will cost more to operate yearly than tank-type electric water heater. If unit has 4500 watts elements, then it will draw 56 amps at full blast, and use a good percentage of household power.

Tankless water heaters have no hot water in power outage. This is true for gas and electric models.

Additional resources:

Bosch 1600H-NG... | Answered on Aug 05, 2011

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