20 Most Recent Bosch AquaStar Indoor Natural Gas Tankless Water Heater with Vent Hood #125 Questions & Answers


That particular tankless water heater has hydro-generated ignition. In order for it to function, it requires a certain water pressure and velocity. You can try turning on the hot water in two location in your house to see if that gets it started. If it does, try getting a higher flow shower head, or removing the limiters in your faucets.

Bosch AquaStar... | Answered on Jan 31, 2019


Green can indicate a water leak .you would have to check for a leak to be sure

Bosch AquaStar... | Answered on Feb 17, 2018


The problem is excessive down draft or condensation. Air flow is important in combustion appliances. Too much airflow down the chimney can blow the pilot out. This is readily apparent when it gets cold and there is air rushing down the chimney in the winter. There may be an air leak in the room with the water heater. While there should be a combustion air supply that is sufficient, there should not be a place for the air coming down the cold chimney to go. That would eliminate the draft. Another thing is if a furnace is in the same room and does not have enough air to supply the burners. IF it is an older furnace without a combustion exhaust fan or has its own flue, the air being drawn into the furnace burners may be blowing the pilot out. Last but not least is the condensation issue. When cold water enters the tank it can cause water to condensate on the outside and drip down into the burner and put the pilot out.

Bosch AquaStar... | Answered on Feb 01, 2018


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 ?

Bosch AquaStar... | Answered on Mar 11, 2017


possible faulty pressure switch connected to the water line and that is failing to turn on the main gas tap solenoid
best have it checked by an accredited gas fitter or service center for the make

Bosch AquaStar... | Answered on Aug 20, 2016


Check to make sure the flame of the pilot is hitting the thermocoupling. If not then you can use compressed air to clean the pilot port and relight and check again. If the flame is hitting the thermocouple, then it may need to be replaced.

Bosch AquaStar... | Answered on Oct 01, 2014


I would question the Thermo couple. It pretty much runs the whole show. Inexpensive quick fix. It's the small tubing that is connected to the gas valve. The other end is a bulb that sits over the pilot flame.. Remove the old and match it up at the hardware store. Install new coupler ensuring bulb is directly over the pilot flame Common iten. The thermocoupler alks to the gas valve. If the pilot flame extinguishes (goes out) the bulb cools and shuts down the gas valve so the pilot gas feed doesn't permit raw gas to accumulate, avoiding the need emergency Services. . You will not get the heater to fire until the bulb is good and hot. The red push button ,when depressed will allow the pilot flame to be lit. Hold it down until the heater fires, indicating the T-coupler has reached its operating temp.Good Luck-Ned

Bosch AquaStar... | Answered on Sep 10, 2014


Hold in your pilot button, then push the spark button repeatedly to light your pilot. Once its lit, hold that pilot button in for 30 seconds to heat your thermocouple. once its heated, release the button, and slide the slider to burner position. Turn on hot water fixtures to get the unit to light

Bosch AquaStar... | Answered on May 06, 2014


C7 code has to do with your main fan. Either its not working due to it being blocked or having gotten wet/damaged/power surged, or your control unit isn't supplying the correct 120V to the fan. Your control has a ceramic fuse that you can test as well.
First, look for 120V to either the left or right pair of wires in the molex plug on the fan. if you have voltage, then the fan is bad. If you dont, its either just a fuse, the board is bad, or the fan is bad causing the fuse to blow. Insert the supplied spare fuse, and power up the unit. If it blows the fuse again, its the fan.

Bosch AquaStar... | Answered on May 06, 2014



Bosch Aquastar 125B Water Heater Repair Parts Pre January 2003

Bosch Aquastar 125B Repair Parts Selection Grid

This web site has Aquastar 125B parts. It appears your unit was manufactured 7/7/02, so that is what I pulled up for you. At least this will be a start for you to locate the part. I hope these links work.






Bosch Aquastar 125B Water Heater Repair Parts Post February 2003

Bosch AquaStar... | Answered on Mar 27, 2014


sounds like pressure relief valve is stuck closed free of or replace

Bosch AquaStar... | Answered on Oct 12, 2013


Kathy, dont mess with it. get an engineer

Bosch AquaStar... | Answered on Sep 05, 2013

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