I have a Bosch Aqua Star AQ 125 B top vent water heater purchased from Menards in July of 2001. Absolutley love this unit and it have performed flawlessly for over 8 years. But for the last 3 weeks, when we take a bath or shower, when you turn off the hot water, the burners stay flame on...not full mind you, but say half of the call for the hot water in the shower. Now, when this happens, there is a bunch of knocking and banging in the pipes(forgot the term). So, I would go turn on the cold water first, then the hot water to release the pressure. This has never blown the pressure safety valve. I have been looking for over two weeks for info of what is wrong. How can a guy fix this. I simply shut the unit down when I do not need hot water and turn it on when I do...but that cannot be a good long term fix. Please help!!!!
We have a Aqua Bosch 125B tankless water heater. We bought and replaced all the parts.Problem is the pilot light stays lite but the burners will not ignite. Water pressure is good.
Ok the way this system works is from a pressure and flow switch. The pressure switch picks up the slight drop in pressure when the hot side water is turned on then turns on the burner. The flow switch measures the amount of water flowing and adjusts the size of the burner to the amount of water flow. So a couple different things might be happening. The flow switch might be sticking causing the water heater to throttle down the burner but not off when the water flow is off. Or the gas control valve might be by-passing gas when off causing the burner to stay on even when the demand is off. Run the hot water on high demand then turn the water off. If the burner is still on try banging on the water heater with your hand and see if the burner shuts off completely. If it does the gas control valve might be by-passing. You would also need to check and see if the pressure/flow switch is giving any voltage signal changes when the water flow is off. These tankless water heaters are more comlplicated to work on than a standard water heater and you may need a professional's help...good luck
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