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View Full Version : Bosch tankless water heater does not heat after first run


pcarmichael
Sep 11, 2010, 07:19 PM
I have the Bosch Aquastar 125X. When I turn on the water first thing in the morning, the pilot lights and the burner lights as it should. If I turn off the water and turn on the hot water again, the pilot will light but the burner will not. If I go into the laundry room where the Bosch is installed and run the water there 3 or 4 times, the burner will light. I have tested and repositioned the thermocouple a couple times but that does not seem to help. If history repeats itself, and it has done this cycle twice in the past 4 years, eventually the pilot will refuse to light and I'll have to replace the master control box. I have replaced the master control box twice in the past 3 years. After replacing, the heater is perfect for about 6 months then goes into this cycle of only lighting first thing or after sitting for hours, then it needs fiddled with to light the burner. The batteries are fresh in the ignition circuit. Anyone have any experience with this device? Should I stop throwing good money after bad and get a regular tank water heater?