Question about Terminator Aquastar 125FX Tankless Water Heater: FX Hood Horizontal Vent

5 Answers


The water heater won't ignite promptly. It takes turning on the water 5 to 10 times before it will ignite. It is 5 years old. It has worked great until last 6 months.

Posted by STEVE ENABNIT on

  • 2 more comments 
  • debbie05 Feb 12, 2008

    having problem with the tank not igniting. have to push reset button at least once per day, this unit is an outdoor model

  • Anonymous Apr 19, 2008

    continue to get er code - what to do please

  • Anonymous Nov 12, 2008

    I have the same problem. The pilot does not go on all the time. Sometimes I have to turn the hot water on and off a few times at the faucet. I tried rebuilding the water valve. No luck. I tried replacing the piezo. No luck. I tried replacing the thermocouple. No luck. I tried replacing the pilot tube (assuming it had a clog). No luck. The only thing that seems to work right now is to unscrew the pilot from the burner assembly and just let it hang there an inch away from the burner. This seems to resolve the problem, but is, as you can imagine, not very safe. Short of replacing the electronics, I am at a loss of what would cause it.

    Having the pilot assembly sit 1" outside of the burner works, so I assume it has something to do with lack of oxygen or even a loose wire of some sort.

  • Anonymous Mar 11, 2009

    Same for me. The vent fan starts when the hot water tap is turned on. The pilot does not light nor the burner start. Unfortunately, this is our only source for hot water so I need to get it fixed. Good luck with yours.

    1. Fan starts

    2. igniter does not spark

    3. Pilot doesn't light

    4. Wife yells



5 Answers


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Well, after an hour of internet searching, I can give some real advice.

This website has excellent trouble shooting and illustrated parts breakdowns. They'll even place your parts order too.

For my AQ125FX the problem was the Electronics Control Box (PN 87007207011). I didn't have the 1.3 Volts DC required for the igniter. I also recommend that you check the Water Inlet Filter (PN 8700507059) for deposits and blockage. While there is no specified time change for the filter, I suggest that it be changed at least every 2 years (cheap insurance at $10 a filter). There is a Service / Replacement kit for the Water Inlet Valve (PN 8703406178) if you've got a gummed up valve but it should not be necessary if the following things happen when you turn on the hot water tap:

1. The Exhaust Fan Vent Motor starts
2. The Pressure Demand Micro Switch closes (this is the black device at the very bottom of the unit)

The key to this system is downstream water pressure (demand for hot water) and the Water Inlet Valve and Pressure Demand Micro switch is the heart with the Electronics Control Box being the brains. I hope this helps you with your Bosch Aquastar water heater.

Posted on Mar 12, 2009



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These heaters work when a pressure drop is sensed in the water supply line. The pressure sensor is likely blocked with sediment from the city supply. You may want to call for service.

Posted on Apr 27, 2007



I am unable to locate the reset buttom . I have the AQ125FX if you could tell me where to locate it i would greatly appreiciate your expertise

Posted on Nov 02, 2008


I noticed mine does not ignite properly during the summer. I believe the incoming water temperature may be a factor.

Posted on Oct 22, 2007


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I finally got a heating and plumbing guy to look at my water heater. Turns out the problem was with gas pressure. The pressure was very low coming into the house at at the appliance. He turned up the pressure on the regulator coming into the house and the water heater has been working just fine.

Posted on Mar 23, 2009

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