Troubleshooting
heater. Then open all of the hot water taps served by the heater. Wait 10 minutes and check all taps for water flow. There should be no water flowing. Any continuous flow of water, small or large, indicates a crossover and must be corrected. Consult a professional plumber for help in correcting a crossover. Failing single lever faucets and mixing valves are common causes of plumbing crossovers.
8.Ensure the outlet temperature sensor is making contact and firmly mounted on the hot water pipe.
7.5Low water flow/pressure
1.Too many hot water applications are being used simultaneously or too much flow is demanded. The water heater will effectively support two
2.Ensure that gas pressure is in accordance with specifications in chapter 3.12, page 27. A gas pressure reading is needed to proceed further. Contact your original installer or a local certified gas technician to obtain this reading. If gas pressure is inadequate, the water heater will close its motorized water valve, reducing the hot water flow rate in an attempt to reach the selected output temperature.
3.If selected temperature on the unit is set too high for the demanded flow rate, the water heater will close its motorized water valve, reducing the hot water flow rate in an attempt to reach the selected output temperature. Lowering the selected temperature will allow the motorized water valve to open up for increased water flow rate.
4.Clean inlet filter screen per chapter 6.1, page 32.
5.Inspect the water path for obstructions. Make sure all showerheads, faucet aerators and whole house filters are clear of debris.
7.6Hot water temperature fluctuates at tap
1.Hot water is very hot out of the tap, requiring mixing of cold water in order to attain a useable hot water temperature. The addition of too much cold water will overpower the hot water flow from the tankless water heater.
This slows the flow within the tankless water heater, decreasing it below activation point, which shuts off the burners. The end result is nothing but cold water coming out of the outlet.
Consult www.boschhotwater.com for a detailed service bulletin on overcoming temperature fluctuations.
2.Unbalanced pressure in water lines. Any restriction in the water heater, such as a clogged inlet filter screen, can result in unequal pressures between the cold and hot water lines. In such cases, when mixing in the
higher pressure cold water at the tap, the lower pressure hot water can be overpowered. This will shut down the burners because the hot water flow rate fell below the minimum flow rate required for activation. Verify inlet filter screen is clean and clear of debris. See chapter 6.1, page 32 for inlet filter cleaning instructions.
3.Heater deactivated by temperature balancing valves. If the outlet water temperature is set too high, the heater can produce temperatures that are too hot. A temperature balance shower valve will automatically mix in cold water to reduce the hot water temperature. In the event of any temperature instability at a fixture using a temperature balancing valve, refer to the valve manufacturer for instructions on internal adjustment setting. An adjustment should be made to minimize the amount of cold water the valve is adding. Additionally, the temperature setting on the heater can be lowered to prevent the temperature balance valve from mixing in too much cold water.
4.Inlet water pressure is erratic due to fluctuating supply water pressure. For installation on a private well system with the use of a pressure tank, the lowest pressure range setting recommended is 40- 60 psi (2.75 - 4.15 bar). Consult your installer or local plumber for effective ways to maintain constant water pressure to the water heater when on a well system.
7.7Noisy burner/heater during operation
1.Sealed combustion leak. Make sure combustion cover is securely fastened. Ensure the exhaust vent adaptor is properly sealed with supplied gasket. Leaky seals create improper combustion resulting in noise.
2.Improper venting. Venting that is unsealed, the wrong material, too big in diameter or too long in run will result in unstable burner flames and noise. Ensure venting is proper and in accordance with specifications in chapter 3.3, page 9.
3.Lack of adequate combustion air. Drawing combustion air from a room area of inadequate size will result in unstable burner flames and noise. Improper use of piping for combustion air will result in unstable burner flames and noise. Ensure adequate combustion air is provided to the unit in accordance with specifications in Section 3.4, page 20, Combustion Air Requirements.
4.Cross contamination. Ensure that intake and exhaust terminations maintain minimum required clearances stated in the manual. Cross contamination between intake and exhaust may cause unstable burner flames and noise.
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