Question about Bosch 125BO NG AquaStar Outdoor Natural Gas Tankless Water Heater

1 Answer

The water goes cold after 40sec, have to turn water off and on to get hot water again. Not sure if this is the right model but it looks the same and doesnt have any electricity, 16H natural gas. regards Nicholas Maynor

Posted by on

  • Anonymous Mar 26, 2014

    turn the warm water on and it starts to get warm I electric no gas the lite comes on I have flipped the breakers and still the same thing



1 Answer

Before calling service technician, open following link for Bosch troubleshooting resources

The model and serial number are usually located on label on side or front of unit.
Link above might have your manual where you can read advisories and required maintenance.

If you are not getting error code, then problem could be plumbing related, but this is a shot in the dark, and one of many places to start troubleshooting.
Error codes are starting points, and a problem on one tankless can have entirely different cause and solution than same error code on another tankless.

Upvote the help.
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.

Posted on May 26, 2011

  • Anonymous Jun 01, 2011

    You asked for do-it-yourself help without giving model number or saying what you've done so far to fix problem. If the 100% researched answer is not helpful, then next time take advantage of fixya assistance live and pay expert to ask what model number you have and what you've done so far to fix problem.



1 Suggested Answer

  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

Hi there,
Save hours of searching online or wasting money on unnecessary repairs by talking to a 6YA Expert who can help you resolve this issue over the phone in a minute or two.

Best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.

Here's a link to this great service

Good luck!

Posted on Jan 02, 2017


Add Your Answer

Uploading: 0%


Complete. Click "Add" to insert your video. Add



Related Questions:

1 Answer

Radiators hot no hot water. Luke warm for a bit. Then back cold. Setting is past 'eco' just moved in not used to combi but surely this isn't right

check the diverter valve. look to see if when hot water turned on the small electrical switch at the end operates. If not then a ned valve or diaphragm

Apr 10, 2015 | Water Heaters

1 Answer

Ls80t hot water goes hot cold hot cold heating is ok

What kind of water heater do you have? Boiler, indirect?
What brand and model?
Or is this a HVAC unit?


If you need further help, I’m available over the phone at

Aug 17, 2014 | Water Heaters

1 Answer

Rheem warrior 40 gal warrior

You could start by seeing if the thermostat is wide open. Sounds like it is on low or vacay mode. How far is the run between your heater and the bathing area. Might need to insualet some piping.

If you need further help, reach me via phone at

Sep 24, 2013 | Water Heaters

1 Answer

Sunbeam hot/cold water dispenser is leaking from looks like copper tubing that goes to tank. Model # ylr-5-87h3 what could my problem be

Broken solder connection.
Continual expansion and contraction of metal due to hot and cold extremes will cause metal fatigue. The most vulnerable place is at the join. Other places can fail, but usually the solder join will fail first.
Buy another one and support economy.
Make sure next unit is connected to cold water line, and not hot water line. If hot water dispenser is connected to Hot line, then it will cause water heater to run each time water is drawn through dispenser because cold water immediately enters tank.
You might also consider installing small tank under counter. Tanks are less glamorous than hot water dispensers but tanks are more reliable long term than instantaneous water heaters.

If you need further help, I’m available over the phone at

May 28, 2013 | Water Heaters

1 Answer

Hello we have Bradford hot water tank model #MI65R6DS13. Our problem, I keep having to press the tanks reset switch for us to get hot water. At the same time after I press the reset switch we have hot...

No the top thermostat is the first place I would start to replace. They run about 14.00 more than likely it isn't controling right. Turn power supply to water heater off and replace thermostat.

If you was getting scalding hot and then turning cold without tripping the thermostat it would be the top element working and the bottom one bad.
Bottom element good it will give you luke warm water for a while then gradually turn cold because it's heating the bottom of the tank.

Hope this will help you out.

Oct 09, 2010 | Fasco Bradford White Hot Water Heater...

1 Answer

GAs will not shut off when water is turned off. We already bought and replace the water valve. If we turn off the hot water, it makes a terrible sound and overheats. It eventually goes to the emergency...

Turn Hot Temperature down lowerthan current setting. Make sure that Heater operates properly before using. A defective temp sensor can SCALD and BURN. What TYPE of Terrible SOUND? Do you have anyone tht is the least bit mechanical to observe and direct you to the right source. IF your husband enjoys cold showers this sounds like an opportunity to suggest that with WARM baths the two of you can have some Peaceful time! And both come out clean!

Aug 25, 2010 | Bosch Water Heaters

2 Answers

Bosch AquaStar 125b ng suddenly goes cold during shower

Does it happen to any other fixture? If not, it's most likely your shower valve and not heater.

Sep 01, 2009 | Bosch AquaStar 2400ES-NG

1 Answer

Problem with hot water flowing from cold outlet

The hot and cold pipes run in the wall next to one another. So the water turns cold again as soon as the water starts flowing

Jun 16, 2009 | Honeywell Water Heaters

1 Answer

Water heats for about 3 seconds and goes cold

Take the cover off and look for reset that has trip.If you can't find no reset turn the power off and wait for five minutes,turn on and turn water on also to see if you get hot water.


Not finding what you are looking for?
Bosch 125BO NG AquaStar Outdoor Natural Gas Tankless Water Heater Logo

502 people viewed this question

Ask a Question

Usually answered in minutes!

Top Bosch Water Heaters Experts

Colin Stickland
Colin Stickland

Level 3 Expert

22326 Answers

john h

Level 3 Expert

15148 Answers

Paul Nielson
Paul Nielson

Level 2 Expert

91 Answers

Are you a Bosch Water Heater Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides