I have recently installed a Bosch GWH-635-ES direct vent, NG tankless water heater. I have followed all manufacturing specs & instructions, performed NG load calcs for pipe sizing, and verified appropriate CO2 levels & NG pressure.
The heater works great but for some reason, usually in the morning, or for the first demand over a period of time (4 or 5 hours), the unit emits a low but load resonance that can be heard through most of the house. It only lasts for about 5 seconds but is slowly driving me crazy. It doesn’t even happen everyday, but when it does happen, it seems to occur during the first use. I have called bosch but they have not been of much help and have gone over the unit with a fine toothed comb and have come up empty handed.
I have provided a picture to show my configuration, and it doesn’t show but both intake and exhaust terminate just above where the picture cuts them off.
Any ideas or thoughts would be greatly welcomed. Thanks.
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Flow restricter?