How to fix a Noisy Burner on a Tankless Water Heater

Why my Bosch water heater 1210 is noisy when it is heating the water, and what can I do to fix the problem?

There are several reasons for the annoying water heater noise, and we will review several issues which are shown below. The noise, for example, can also be a signal that something more complex and dangerous is going on.

According to Bosch technical data, the working noise range should be between 45 and 65 dB.

Bosch Therm 1210 ESBosch Therm 1210 ES

The elements that are making most of the noise are the electric fan and gas burner. 

Take advantage of the viewing port to check the burner flames during the operation; the flame should have the regular pattern with the light blue tip and no signs of yellow or red.

Ensure room sealed operation. The tankless water heater must have the combustion chamber properly (factory) sealed for proper work and safe operation. If the combustion chamber is not fully closed or the seal is damaged, it will result in leakage of products of combustion, and you will hear the noise that is louder than in normal, sealed situation.

Check the venting system. The venting system must be done per codes, standards (ANSI, ASTM, CSA, ULC) and manufacturer’s instructions. That means that pipe diameter is not bigger, and the length is no longer than the recommended, the vent pipe is made of the suggested materials, venting and the exhaust vent adaptor are correctly sealed. 

Otherwise, gas combustion will be unstable and improper, which will lead to reduced safety and loud combustion. The recommended vent diameters are 3” and 4” and the maximum lengths are 31 ft. and 63 ft. respectfully, for the twin pipe system. The vent and combustion air connector piping must be sealed gas-tight to prevent the flue gas spillage and carbon monoxide emissions.

Reduced supply of combustion air. As the Bosch water heaters from 1210 series are direct vent models, an adequate air supply must be provided for the safe operation. The air for combustion is taken from the surrounding, and the room where the heater is located should have the proper size. The product of combustion also has to be moved out with the correct piping and with no blockage or obstructions. If one of these two factors is not met, the gas combustion will be unstable and will lead to a noisy operation.

Cross contamination. Make sure that venting and combustion pipes have the proper clearance and are done per codes. In a case of the cross-contamination, the fan rotation reduces its speed and error code C6 appears.

Lack of gas pressure. Ensure that gas pressure is per specs. Minimum inlet gas pressure, under full operation, has to be: 3.5” WC for natural gas and 8” WC for LPG or propane gas. If the requirements are not met, contact the certified technician.

Ensure the proper CO2 readings. The calibrated combustion gas analyzer must be used for verifying the proper CO2 adjustments. It is usually followed by the EA and EC errors, and the leading cause that affects the CO2 level is the improper gas pressure.

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