Question about Bosch AquaStar 125FXKIT-NG 125FX Natural Gas Tankless Water Heater w/ Hood

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Water will not stay hot

My Bosch Tankless Water Heater will not stay hot. The water starts out hot then goes to cold .

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  • sandra_killi Jul 24, 2009

    It worked perfect for 5 months. After that is when the water wouldn't stay hot so I don't think it is water pressure.

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Did you ever figure this out? Ours was working fine and then all of a sudden is luke warm .

Posted on Dec 27, 2010

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The cold main water pressure is too low to maintain a constant flow. Make sure you have no other appliences on, or your not comprimised by the lowering of pressure

Posted on Jul 23, 2009

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Posted on Jan 02, 2017

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Will not fire at all, trys to light but get the e1 code . used to work intermitently or fire right of way but then go cold and back to hot for about five min. then stay hot now wont even light


Before calling service technician, open following links for troubleshoot resources:
http://waterheatertimer.org/pdf/Bosch_E1_troubleshooting.pdf
http://www.bosch-climate.us/bosch-hot-water/aquastar-service-bulletins/
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html
http://waterheatertimer.org/Crossover.html

Before installing tankless water heater, read the service manuals and product manual to make sure you have testing skills and equipment needed to repair tankless gas water heater, and that you are prepared to buy expensive parts when needed and do the recommended yearly and monthly maintenance as outlined in manual.
Also check that area has qualified service technician, and that person carries parts on-hand, and is certified for your model number. Keep Tankless manufacturer contact information on-hand, and be skeptical of promises of unlimited hot water, and effortless long-lasting water heating, and saving money. The only folks saying this are the folks selling the product, and not their customers.

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

Sep 21, 2011 | Bosch Water Heaters AquaStar 250SXO...

1 Answer

Bosch 1600H-NG Natural Gas AquaStar AquaStar Natural Gas Tankless Water Heater. Problems with constant hot water. The heater turns ok but (i think) when i turn on the cold side the heater stops. at...


Possible flow sensor issue. Check to see if your water pressure fluctuates a lot or is fairly steady. These units are sensitive to the pressure. take care.

Feb 19, 2011 | Bosch 1600H-NG Natural Gas AquaStar...

1 Answer

Hot water tank does not work when shower is on, it does however work when the faucet in bathroom is on. It quit working in the shower about a month ago.


  1. COLD MIX, HEATER DEACTIVATES
    If inlet water temperature is over 70°F due to geographic location, water maybe very hot out of the tap. This requires a lot of cold water to be added with it in order to attain a useable hot water temperature. The addition of too much cold water will overpower hot water demand from the tankless water heater. This slows the flow within the tankless water heater, decreasing it below activation point, which shuts off the heater. The end result is nothing but cold water coming out of the outlet. See: TWH E2-04 Overcoming fluctuating temperatures [PDF].
  2. FLUCTUATING WATER PRESSURE
    If the water pressure in the home is erratic and the water flow is not consistent while a tap is opened, then the temperature of hot water will fluctuate. The minimum water pressure for the home should be 30psi or greater. For people on well systems the minimum pressure range is 30-50psi. The use of a pressure reducing/regulating valve is an effective way to maintain constant water pressure to the water heater. Watts brand 25AUB- ¾" or N35B-¾" pressure reducing/regulating valves or equivalent is suggested.
  3. CHANGING FLOW RATE
    Major changes in flow rate can adversely affect the output water temperature of the heater. Increases from one major fixture running to multiple fixtures running at one time can cause the temperature to fluctuate. Stay within the heater's specifications. See: TWH E2-03 Outlet temperature vs. flow rate [PDF].
From the Bosch website.

Good Luck,
Gary

Dec 16, 2010 | Bosch PowerStar AE125 AE125 Whole House...

1 Answer

Bosch tankless pro hot water heater cycles on and off very hot or cold not consistent what lp pressuer is need ? flame goes off while water is running


LP pressure needed is no less than 11 inches of water column while all gas appliances are in operation. Info is in the installation manual near checking CO2 levels.

Jul 19, 2010 | Bosch & Tankless LP Hot Water Heater

3 Answers

Water turns cold very quickly


I had the EXACT same problem (installed my tankless last winter and worked fine, now this summer it fluctuates, have to turn the shower completely off and then on again to get any hot water and then it only lasts for a couple of minutes!) Argh - it is frustrating!

Here's what I found: the demand for hot water is lower during the summer (hot) months because the "cold" water coming in is already quite warm. You don't need as much hot water to make the shower temp comfortable. SO, my tankless was shutting off due to low flow demand. I've removed the flow restrictor from my shower head and it helped alot but didn't completely solve the prob. Next step is what has been recommended to me by several people but is much more expensive - change the pressure valve on your shower to a temperature valve. Or just wait til winter and it should work ok again :)

Jul 06, 2010 | Bosch & Tankless LP Hot Water Heater

1 Answer

Bosch tankless hot water heater: Confort TOO HOT!!!


Look for a water temp control on unit. Otherwise a lower temp can be attained by having a higher water flow to minimize temperature buildup in heating coil.

Sep 06, 2017 | Bosch & Tankless LP Hot Water Heater

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

Bosch water heater


I'd initially check for a cross connection (cold water leaking into hot water system). This can be done by shutting off the cold water feed to the tankless unit, then opening up hot water fixtures around the home. You should see the water come to a complete stop; if you see a steady stream of water, then you have a cross connection. The most common place for a cross connection is at single handled showers. The valve cartridge starts to fail over time.

Jul 09, 2009 | Bosch & Tankless LP Hot Water Heater

1 Answer

Error EA


Welcome to Fixya
you have a Bosch tankless water heater your heater is not pumping out hot water?
Please send model # Thankyou

Dec 15, 2008 | Bosch & Tankless LP Hot Water Heater

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