Bosch Aquastar 125FX LP Water Heater Not Working

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Dbohn75

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I have a second tankless heater in our home and it has worked great for a number of years. Over the last few months it has randomly stopped lighting and now will not light at all. I have cleaned the pilot and burners, replaced the main water valve and have tried to bypass the pilot by using a torch with no luck. I think its either the main control box which is not tripping the ignitor or maybe a ECO overheat sensor, neither one is cheap but I'm looking to see if anyone has experience troubleshooting or a service guide for them.

Here is a link to user guide and parts listing.... user manual

Just parts info ... parts diagram
 

Fitter30

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With electronic ignition if u use a torch and it's not going to lite unless burner is calling for pilot the same time burner calls for it or else it will lock out. A torch will only burn up the flame rod and igniter. Without reading a service manual and a code its a guess. Frame rods use m.a.
 
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WorthFlorida

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Possible the gas regulator went bad. See page 10.
This is the manual, it has a good check list and list of features on Page 2 that gives a path on what to check. Page 12 list steps for proper lightening sequence.


Lightening the pilot with anything will not work on this unit. It not like a continuous pilot light flame. It seems gas is just not flowing.
6. Turn the hot water faucet on to the minimum flow required
to activate the heater. The automatic ignition system
first ignites the safety pilot burner which then ignites the
main burner in about 4 seconds. The power exhaust will

then activate.
 

Dbohn75

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With electronic ignition if u use a torch and it's not going to lite unless burner is calling for pilot the same time burner calls for it or else it will lock out. A torch will only burn up the flame rod and igniter. Without reading a service manual and a code its a guess. Frame rods use m.a.
Correct i had a very small torch going at the exact same time the burner should have been active when a faucet was turned on. This was a simple check recommended by a service person on another site just to see if its as simple as the ignitor being bad. There is no digital display to show error codes on this model.
 

Dbohn75

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Possible the gas regulator went bad. See page 10.
This is the manual, it has a good check list and list of features on Page 2 that gives a path on what to check. Page 12 list steps for proper lightening sequence.


Lightening the pilot with anything will not work on this unit. It not like a continuous pilot light flame. It seems gas is just not flowing.
6. Turn the hot water faucet on to the minimum flow required
to activate the heater. The automatic ignition system
first ignites the safety pilot burner which then ignites the
main burner in about 4 seconds. The power exhaust will

then activate.
I was thinking that could be the problem or the pilot electrovalve could be bad. Without a true service manual its kind of a guessing game.
 

John Gayewski

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Without an error code you have to go through each component with a meter and check them one by one.

Two things to check. Do you have anything else plugged into the receptacle along with this heater (a sewing machine for me once)? Or on the same circut even. The heater should be on its own circut. This can fool the control board.
 

Dbohn75

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I think the basement lift pump and this has been on the same outlet/circuit for the last 16 years. I did try another outlet with no luck.
 

Fitter30

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Correct i had a very small torch going at the exact same time the burner should have been active when a faucet was turned on. This was a simple check recommended by a service person on another site just to see if its as simple as the ignitor being bad. There is no digital display to show error codes on this model.
NEVER!!!
would recommend anyone light a pilot with a torch. If a hot surface or spark won't light it there is another problem. Manufacturers and codes protect themselves from any liability. Thats why if u would read the install or service manuals their are all kinds of notices, warnings and DEATH.
 
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Dbohn75

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NEVER!!!
would recommend anyone light a pilot with a torch. If a hot surface or spark won't light it there is another problem. Manufacturers and codes protect themselves from any liability. Thats why if u would read the install or service manuals their are all kinds of notices, warnings and DEATH.
The point of using a different source is to see if the ignitor is bad or not, I'm not using a large propane torch just a very small butane which has a flame the size of the pilot.
 
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