Question about Bosch AquaStar Natural Gas Tankless Water Heater #125B-NG

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AquaStar 125b ng will not heat water past lukewarm. Pilot is good, burners fire, cleaned out inlet filter....I have noticed that the water pressure does not change with the flow/temp control turned all of the way clockwise which should restrict the flow. Is it safe to assume that this is a water valve issue?

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6ya6ya
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Posted on Jan 02, 2017

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heatman101
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SOURCE: I have a Bosch 125x

Hi,

That sounds like there is dirt in the pilot orfice... that can be very hard to get out and even harder to clean....the hole is like smaller then a pin hole...

heatman101

Posted on Nov 25, 2010

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SOURCE: Water is way too hot.

Before calling service technician who has service manual and can test which part has failed, open following links for troubleshooting resources including steps below and phone number for Bosch:
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html
http://www.boschhotwater.com/HelpfulResources/TechnicalSupport/BoschAquaStarModels/2400ETechSupport/Troubleshooting/tabid/1131/Default.aspx

Clean inlet filter
Check all faucets for clear pathway
This unit does not work with preheated water (solar assisted)
Incoming water above 70 degrees, avoid restricted faucets
Check that both temperature sensors are making contact and firmly mounted on respective cold and hot pipes.
Descale heat exchanger
http://www.boschhotwater.com/Portals/7/TechBulletins/TWH-G2-13_Descaling.pdf

Posted on Aug 16, 2011

SOURCE: how do you change out a water valve in a aquastar

There are service bulletins concerning water valve rebuild and water valve retrofit that may be useful:
http://www.boschhotwater.com/HelpfulResources/TechnicalSupport/BoschAquaStarModels/125BTechSupport/ServiceBulletins/tabid/384/Default.aspx

From retrofit service bulletin:Old brass valve is replaced with improved plastic water valve.
Two sets of screws hold water valve against gas valve.
Descale water valve with CLR if it will not remove easily.
Call 800-642-3111 for help

Fix most tankless water heater problems yourself, same day for about $350.
http://waterheatertimer.org/How-to-install-gas-water-heater.html

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Posted on Sep 04, 2011

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1 Answer

Bosch aquastar 125b


Thermocouple which on that model can be just the Thermocouple or a larger loom with the thermocouple in it depends. Call or look up Houseneeds.com they have parts.
If it was the magnet you wouldn't get any gas to manually light pilot.

Jun 06, 2014 | Water Heaters

2 Answers

Eratic hot water flow


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.

Mar 14, 2014 | Bosch 1600H-NG Natural Gas AquaStar...

1 Answer

Bosch aquastar wont get hot


1) If tankless is not showing error code, the problem might be single-handled faucet cartridge:
http://waterheatertimer.org/Crossover.html
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

2) Catch up on maintenance, such as cleaning combustion parts, have gas pressure checked, etc.

Feb 20, 2013 | Bosch AquaStar Natural Gas Tankless Water...

1 Answer

Bosch 125b-ng water heather has low flame only


Did you check to make sure the shut off handle is on the on position?

Dec 19, 2012 | Bosch AquaStar Natural Gas Tankless Water...

1 Answer

Once in a while after burner has been on and shower has been on for a while, the burner shuts down and pilot flutters, then pilot comes back on good but no burner .eventualy burner comes back on. if i turn...


Probably the burner and parts need to be cleaned yearly as recommended in most gas water heater manuals. Both tank and tankless today recommend same.
Open following link for Bosch troubleshoot resources:
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

Jun 20, 2011 | Bosch AquaStar Natural Gas Tankless Water...

1 Answer

I have a Bosch Aquastar 125ng with the water turbine ignition. When you turn on the water, it works exactly as expected. If you shut off the water and then turn it on again, it will not always start. It...


i have an aqua star 125 ng an the pilot lights and stays lit but the main burners wont fire up when i turn the water on i have good water pressure so i kind of stumped and i just rebuilt the diaphram in it also

Dec 11, 2009 | Bosch AquaStar 125FXKIT-NG 125FX Natural...

2 Answers

The pilot goes off and on and does not light the burner


ok make sure u turn everthing thing off then wait 5 min then turn the dail that controls the heat on it to pilot light then turn the gas nob to pilot then ignit it once lit wait a few seconds and turn gas nob to on pisition then turn heat dail to were the arrow is not to a b or c cause the gas is to high it will blow it self out

Nov 17, 2009 | Bosch 1600H-NG Natural Gas AquaStar...

1 Answer

Gas tankless water heater turns off during shower


Take the thermocouple out and match it up at any hard wear store. Maybe $10. Replace it .Make sure the flame is clean and hitting the rod in the center center. Ajust (Bend) accordingly.

Feb 23, 2009 | Bosch 1600H-NG Natural Gas AquaStar...

1 Answer

AquaStar 125B NG continues heating water when no demand


I found the manufactures website and read this specific tech bulletin. I will be replacing or repairing my water value soon.

http://www.boschhotwater.com/Portals/7/TechBulletins/TWH-G1-25_Water_valve_rebuild_B.pdf

The bulletin said the following:
If the burners fail to go off immediately when the
water is turned off, usually due to mineralization in
the water valve on older heaters. To test for this
possiblilty, run hot water at a faucet, then shut off
the cold inlet supply and observe if the burners go
off immediately. If they do not the Aquastar will
overheat and shut down on safety depending on
the delay.

Jan 11, 2009 | Bosch & Tankless LP Hot Water Heater

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