I have a 16h Bosh hydropower hot water heater . The unit suddenly has no spark .I have taken off the little generater cap and thouroughly cleaned it and the internal turbine . With no improvement . All gas etc is good

when you turn on the hot water tap there is a pressure switch in the line that sends a signal to a gas solenoid to pass the gas and at the same time to the pizo to start the flame
I would have that pressure switched checked as it may be sticking ( internal contamination) or have dirty corroded points
as gas is involved I would suggest a gas technician do the jib
when you turn off the tap, that pressure switch is shut off so the gas is turned off at the solenoid and the pizo is stopped.

The Bosch Hydropower units have poor electrical design, anyway assuming the heater is working properly, I would get it serviced for this that is <(TURN OFF GAS>), backflush water circuit, just unplug in and out water pipes and connect a hose to the outlet its easy enough to find a fitting or something, but you may need to bend the pipes around a little but do not hurt them!, the crud buildup in the pipes will reduce your efficiency like if you use it with unfiltered rain tank water you would want to clean it about every 5 years on the other hand if you have hard water as in bore water then I dont know but I think calcium buildup will be your problem. hard water clogs up everything, disassemble and clean out water inlet manifold, there is a mesh screen in there, on mine it was in bits all through the ports clogging everything up. Now if needed clean over the whole unit with compressed air to spruce it up and reduce fire hazard or if your diy then it's nice to clean things before working on them imo. Don't ask me what all that would cost!
You don't need to mess round with the gas side that's all fine.

Now here's what you do to fix em, this is for a Bosch Hydropower 10H but I assume it probably applies to the other hydropower models too. Ok for those wanting more information the water flow runs the electronics @ 1.5v DC wich charges the high voltage pilot igniter but it also runs the 2 solenoids for the pilot gas circuit and that pilot circuit operates the diaphragm for the main gas valve. The thing is those 2 little solenoids are grounded through the whole unit, if you look it,s not great, so what I did was add a piece of wire say 5 amp should be heaps, now connect the wire to the fixing point for ground next to the electrical box and now connect the other end to one of the chunky screws that holds on one of the gas solenoids(DON'T REMOVE SOLENOIDS UNLESS YOUR REPLACING THEM THEY ARE VERY FRAGILE AND DON'T ABSOLUTELY DON'T UNSCREW THE SCREWS ON THE LITTLE COLORED PLASTIC BIT, That said I used the green one at the back, don't worry it wont leak gas as long as you only remove one screw but of course (>TURN OFF THE GAS<). Tighten up all the screws, again it doesnt hurt to go over the unit and check all the screws and bolts, there is one screw for calibrating the sliding knob also. And that's it turn on the gas and water and go test your brand new water heater!
More info, you can test the generator with a multimeter, just unplug it and test the voltage with the water running through it obviously. Mine was about 1.6v
You could also test the resistance of the gas solenoids with and without extra wire, etc.
Fyi there is a brass screw about half way up on the left side of the unit facing out that I use to bleed the gas line, at least that's what I use it for. Just unscrew it a bit while its trying to light you just have to flick the switch a few times until the gas comes through then screw it up again.
Also it doesn't hurt to go over everything with some soapy water in a sprayer to check for gas leaks especially if unit is old or if you can smell gas, I imagine if there was a gas leak inside the cover that would cause some issues.
Anyway you wont believe how well it works after this mod, it ALWAYS starts as long as u have gas, it will stay lit at pretty low flow levels so you can mess round with the cold tap and it wont cut out to a point, I used to just have the cover off cos I was always messing with it trying to get it to light or tuning the knobs man it drove me nuts. Now I just leave it at the mid point between my summer and winter settings.
I also disconnected the lights to help it work better but I think that's overkill. You don't really need to blast the hot tap anymore if you have enough flow it will just come on.
Oh and if you still need or want to better control the temps then get plumber to install a tempering valve. The flow control knob I just have cracked open but I think If you have not enough pressure at hot tap you could open flow more and also turn up the heat more.
P.S. my 10H was about 10yo when I serviced it.
The Wizz.

Sounds like you have a hydro-generator on this unit. Check the output on the hydro-generator it should be about 1.5V DC. If not clean the inlet screen and check your water pressure. Water pressure less than 30 PSI will cause issues. If you have 1.2V-1.5V DC make sure the power switch is on. If the power switch is on replace the control unit. I sell parts for Bosch units only!

The Bosch Hydropower units have poor electrical design, anyway assuming the heater is working properly, I would get it serviced for this that is <(TURN OFF GAS>), backflush water circuit, just unplug in and out water pipes and connect a hose to the outlet its easy enough to find a fitting or something, but you may need to bend the pipes around a little but do not hurt them!, the crud buildup in the pipes will reduce your efficiency like if you use it with unfiltered rain tank water you would want to clean it about every 5 years on the other hand if you have hard water as in bore water then I dont know but I think calcium buildup will be your problem. hard water clogs up everything, disassemble and clean out water inlet manifold, there is a mesh screen in there, on mine it was in bits all through the ports clogging everything up. Now if needed clean over the whole unit with compressed air to spruce it up and reduce fire hazard or if your diy then it's nice to clean things before working on them imo. Don't ask me what all that would cost! You don't need to mess round with the gas side that's all fine. Now here's what you do to fix em, this is for a Bosch Hydropower 10H but I assume it probably applies to the other hydropower models too. Ok for those wanting more information the water flow runs the electronics @ 1.5v DC wich charges the high voltage pilot igniter but it also runs the 2 solenoids for the pilot gas circuit and that pilot circuit operates the diaphragm for the main gas valve. The thing is those 2 little solenoids are grounded through the whole unit, if you look it,s not great, so what I did was add a piece of wire say 5 amp should be heaps, now connect the wire to the fixing point for ground next to the electrical box and now connect the other end to one of the chunky screws that holds on one of the gas solenoids(DON'T REMOVE SOLENOIDS UNLESS YOUR REPLACING THEM THEY ARE VERY FRAGILE AND DON'T ABSOLUTELY DON'T UNSCREW THE SCREWS ON THE LITTLE COLORED PLASTIC BIT, That said I used the green one at the back, don't worry it wont leak gas as long as you only remove one screw but of course (>TURN OFF THE GAS<). Tighten up all the screws, again it does'nt hurt to go over the unit and check all the screws and bolts, there is one screw for calibrating the sliding knob also. And that's it turn on the gas and water and go test your brand new water heater! More info, you can test the generator with a multimeter, just unplug it and test the voltage with the water running through it obviously. Mine was about 1.6v You could also test the resistance of the gas solenoids with and without extra wire, etc. Fyi there is a brass screw about half way up on the left side of the unit facing out that I use to bleed the gas line, at least that's what I use it for. Just unscrew it a bit while its trying to light you just have to flick the switch a few times until the gas comes through then screw it up again. Also it doesn't hurt to go over everything with some soapy water in a sprayer to check for gas leaks especially if unit is old or if you can smell gas, I imagine if there was a gas leak inside the cover that would cause some issues. Anyway you wont believe how well it works after this mod, it ALWAYS starts as long as u have gas, it will stay lit at pretty low flow levels so you can mess round with the cold tap and it wont cut out to a point, I used to just have the cover off cos I was always messing with it trying to get it to light or tuning the knobs man it drove me nuts. Now I just leave it at the mid point between my summer and winter settings. I also disconnected the lights to help it work better but I think that's overkill. You don't really need to blast the hot tap anymore if you have enough flow it will just come on. Oh and if you still need or want to better control the temps then get plumber to install a tempering valve. The flow control knob I just have cracked open but I think If you have not enough pressure at hot tap you could open flow more and also turn up the heat more. P.S. my 10H was about 10yo when I serviced it. The Wizz.

take the cover off the 10 h unit light up the burner by turning on the tap turn the water flow tap on the front of unit (white knob) clock wise slowly feel hot water pipe coming out off unit when temp increases put cover back on check temp at sink if too hot turn knob anti clock wise

Look for the error code on heater. Go to: http://www.boschhotwater.com/HelpfulResources/TechnicalSupport/BoschAquaStarModels/2400ETechSupport/Troubleshooting/tabid/1131/Default.aspx

For technical support on your heater.

the unit should still be under warranty sounds like a sticking solenoid problem

There's a filter on the cold water side of the unit. You'll notice a black, plastic, cylindrical component directly below the unit on the cold water line pointing to the left. If you shut of your water and unscrew that cap, there will be a filter attached to the other end.

If the filter is clean, I'd recommend calling tech support for help. You might have an error code.

I installed a tankless heater in my home, I had the same problem, I discovered that the unit was not adequate for the water flow that I needed, I went up to a bigger unit and solved my problems, check to see what the flow rate is recommened for yours

I have just dug my manual out (16H) because mine is faulty. email me and I will photocopy it at work this week and email it back to you.

Installation should be pretty straightforward and the manual's not that in depth. There are however some sections on adjusting the gas and the like that you might want to read over.

mchankey at gmail.com

regards
Mark