Question about Bosch & Tankless LP Hot Water Heater

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I have a Bosch GWH 425 HN Tankless Hot Water Heater...On 2/28/2010, it began intermittant exploding when demand for hot water occurred. Local technicians worked on the unit several times, changed and serviced various parts, consulted with Bosch and never did figure out what was wrong. At one point, it suddenly began working OK and has been flawless for about 2 months. Now, suddenly, it fails to ignite again and a minor explosion occurs. What's the problem?

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  • vicki sullins Aug 12, 2012

    Mine is doing the same thing! IT"S SCAREY! Bought it in March,2009. Any more on this problem ?

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I have the same problem with the same model. The problem has been identified by a friend of mine, correctly, I think.
This is a very dangerous problem involving Bosch's much touted safety feature, ironically enough. IT IS THE FLAME SENSOR IN THE GAS VALVE. The flame sensor is supposed to confirm that the pilot has lighted BEFORE the main gas line sends gas to the main burners, after which the pilot shuts off. The pilot light is not coming on, the sensor that shouldn't let gas fto the main burners is failing and the main gas is flowing and ignighting from the spark that is supposed to light only the pilot in a big explosion.
This is the 2nd unit of this model that has failed. I think Bosch should do a recall

Posted on Feb 04, 2011

  • vicki sullins Aug 15, 2012

    Wondering if this actually did fix the heater. Mine is doing the same thing.

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