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

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Bosch AQ 125 FX will not ignite. pilot lites everytime the gas rails do not. turning water on and off 5-10 times uit will ignite and be fine. Any thoughts?

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Posted on Jan 02, 2017

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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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