Question about Bosch Water Heaters AquaStar - Tankless Gas Water Heater - 1600H

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Looking for a flow sensor for Aqua Star 240 FX

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Here it is..

The Tagaki TK-1 is the same unit and the parts are interchangeable...


Posted on Mar 16, 2011


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My Bosch aqua star water heater lights but won't heat my water

Unplug micro switch located on bottom of water heater if it has one

Dec 30, 2012 | Bosch AquaStar Indoor Natural Gas Tankless...

1 Answer

Looking for a flow sensor for Bosch Aquastar 240 FX

Open following link for Bosch tankless troubleshooting resources including parts, Bosch contact information, typical manuals, error codes, tech support, fuel-saver calculator, water heater forum, fixya links, disclaimers, and for finding service technician.

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Mar 16, 2011 | Water Heaters

1 Answer

I have a aqua star 125 bng-l ser 9650617 the only way i can get water hot is by turning on the shower annd the bathroom tap on?

These type of heaters require a minimum amount of water flow. If your showerhead is the most common flow-restricting type then perhaps it is not permitting the minimum amout of gallons per minute to flow through the unit for it to remain engaged. You might have to try removing the flow restrictor :(

Feb 04, 2011 | Bosch AquaStar Natural Gas Tankless Water...

1 Answer

I have a Bosch Aqua star 240 fx tank less water heater. The unit will ignite and run for 5 sec (Flame visible through window) the flame goes out and it reignites and runs for 5 more seconds and again goes...

It sounds to me like you tried about everything I would. So I think you're already thinking about what I would do next. Try the flame sensor,and as last resort check all connection . Remove wires one by one clean and reattach. If all else fails change cotrol board. It's very hard to fix when it's not consistent. Good luck. Thanks

Nov 15, 2010 | Bosch AquaStar Indoor Natural Gas Tankless...

1 Answer

It's a power star ae 115 i have power to it 240 v

Bosch will give free tech support to figure out your problem. 800-798-8161. Check your paperwork if it is still in warranty they will send free replacement parts. If out of warranty go to for replacement parts. Check the "Flow switch" a long two tubes with two little micro switches and a little round hat or sombrerro that MOVES when the H20 is turned on. IF YOU HAVE ONE OF THESE, it should turn on one or two micro switches. If you have this part it should be described in your "Owners manual". If you no longer have the owners manual you can get one free at It will give you trouble shooting guide and or you can call them even out of warranty then purchase replacement parts.

May 25, 2010 | Bosch PowerStar AE115 Tankless Water...

2 Answers

Burners will not disengage after shutting off Hot Water.

Ok the way this system works is from a pressure and flow switch. The pressure switch picks up the slight drop in pressure when the hot side water is turned on then turns on the burner. The flow switch measures the amount of water flowing and adjusts the size of the burner to the amount of water flow. So a couple different things might be happening. The flow switch might be sticking causing the water heater to throttle down the burner but not off when the water flow is off. Or the gas control valve might be by-passing gas when off causing the burner to stay on even when the demand is off. Run the hot water on high demand then turn the water off. If the burner is still on try banging on the water heater with your hand and see if the burner shuts off completely. If it does the gas control valve might be by-passing. You would also need to check and see if the pressure/flow switch is giving any voltage signal changes when the water flow is off. These tankless water heaters are more comlplicated to work on than a standard water heater and you may need a professional's help...good luck

Sep 23, 2009 | Bosch AquaStar 125FXKIT-NG 125FX Natural...

1 Answer

Can't regulate water temperature

Slower the flow hotter the water is how it works . Sounds like the water section is blocked and could well need cleaning out . Draw back with this system is you need a good inlet flow and flow will drop when you open other taps . they are good for a small house a family house not that good . Not much you can do put in a bigger water inlet to heater ?

Mar 10, 2017 | Bosch AquaStar Indoor Natural Gas Tankless...

1 Answer

Reset keeps triping
click on this link and it has the troubleshooting in strucktions for the unit . hopt that it helps you out.

Jan 11, 2009 | Bosch Water Heaters

1 Answer

I have a aqua star 250sx lp tankless water heater that i have to keep resetting. seems to trip when the water flow is high i tried to look for a manual but no luck. help thanks brian

you should have no more then 75lbs of water pressure going thru the unit and min of 60lbs these are the pressures they are designed to work under, you may have to add a regulator to the system

Jan 11, 2009 | Water Heaters

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