Question about Bosch AquaStar Indoor Natural Gas Tankless Water Heater with Vent Hood #125

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I'm working on a Bosch Aquastar 125 and replaced the diaphram and water valve. ONE of the three faucets this unit serves only gets tepid H2O, even though it is drawing 1.5+GPM. Why would two faucets work and one not get hot? Thanks, Jay

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Balancing spool on the faucet ?

Posted on Feb 04, 2010

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The other day our Aquastar 125 pilot went out. No problem, I relit it. It has gone out several times since then. But when I relight it, it often turns the burner on as if the faucet is running. AF


Safety valve is overheated water.
Sounds like the flow control sensor or other sensors, or pc board are bad.
You need service technician to diagnose problem and replace part.

Or replace whole thing with tank-type heater.
http://waterheatertimer.org/How-to-install-gas-water-heater.html

Gene

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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

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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.
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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.
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Clean water filter yearly or monthly. Page 16 example manual.
http://waterheatertimer.org/pdf/Bosch-125BO-NG-LP-outdoor.pdf
Shut off the installer supplied cold water supply valve.
Disconnect water pipe going to the back of the water
valve. Remove filter from back of water valve. Clean the
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damaged. Inspect the top of the water valve for signs of
a water leak or corrosion. If present, rebuild the water
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Bosch service bulletins:
http://www.bosch-climate.us/bosch-hot-water/aquastar-service-bulletins/38b-125-series-bulletins.html
Descale heat exchanger yearly.
http://waterheatertimer.org/pdf/Bosch_Descaling-heat-exchanger.pdf

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