Question about Bosch AquaStar 125FXKIT-LP 125FX Liquid Propane Gas Tankless Water Heater w/ Hood

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Bosch AQ 125XNG water heater burner frequently won't light

The ignition flame always comes on, but the burner will not light 75% of the time, and often only when we first turn on the highest demand tap in the house, the washing machine set to hot, before we can open another tap and expect hot water out of it. But not even that works much of the time. Sometimes I can get it to light by blowing with all my might into the pilot flame and jumping back before my hair gets singed, but that usually doesn't work either. I checked the battery voltage and they are over 1.4V so that doesn't seem to be the problem (instructions say only need replacement when below 1.2V). Replacing them doesn't always help anyway. But the "clicking" when the water is turned on varies greatly in speed. When it is slow, I know the burner won't catch. When it is rapid there's a much better chance that it does.
What gives???

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May be That we have something we can try. first, what doesn't work most of the time? Blowing with all you mite or jumping out of the way before your hair gets singed?
I think it sounds like you might have a maladjusted ignitor. Mispositioned. Its not in the gas path. Sometimes this happens as the tungsten ignitor wears down. That can be adjusted by repositioning the ignitor so it is in the pat of the gas. Just don't test as you go. Set the ignitor so the arc is about 1/4 inch long and about 1/4 inch away from where the gass comes out. Keep clear of the access hole. The longer it takes to ignite, the more gas build up there is. Have your exhaust vent checked. restriction keeps it from drafting and drawing enought air to balance the air gas mixed to ignitable.

Be careful and be safe

Posted on May 18, 2009

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