Troubleshooting

Test by following 4th bullet under BURNERS DO NOT IGNITE WHEN HOT WATER IS TURNED ON.

LOW WATER FLOW/PRESSURE

•Too many hot water applications are being used simultaneously or too much flow is being demanded

The GWH-635-ES will effectively support two 2.0- 2.5 gpm shower heads simultaneously or multiple sink applications. Greater draws will result in increased pressure drop and reduced flow at taps. See flow/temperature chart on page 22.

•Btu input is too low due to inadequate gas line sizing

See specifications in chapter 2.10 - 2.12. The GWH-635-ES requires adequate gas pressure to reach expected temperatures and flow rates, to compensate for inadequate gas supply or lack of gas pressure the GWH-635-ES will effectively reach the selected output temperature, but only by reducing the hot water flow rate. Its motorized water valve makes this adjustment. Proper gas pressure will need to be delivered before the motorized water valve will allow greater flow rates through it. Lowering the set temperature will also allow increased water flow rate through the motorized water valve. See flow/temperature chart on page 22.

•Cold water inlet filter screen is dirty

Remove water inlet filter screen and clean. The screen is located at the inlet connection to the water heater, disconnecting the main cold supply line at the heater is required. Check and clean faucet aerator screens too.

HOT WATER TEMPERATURE FLUCTUATES / UNIT DEACTIVATED

•Unbalanced pressure in water lines

Any restriction caused by the water heater in the hot water system can result in uneven pressures between the cold and the hot. In such cases when mixing cold water at the tap (manually or automatically through a mix-type shower valve) the lower hot water pressure may be overpowered by the higher cold water pressure in the building and cause the hot water flow rate to fall below the minimum rate required. A pressure balance valve will help to resolve this symptom.

•Temperature balance valves

If the outlet water temperature is set too high, the heater can produce temperatures that are too hot. A temperature balance shower valve can automatically mix in cold water to reduce such hot water temperature. In the event of any temperature instability with the use of a temperature balance shower valve, refer to shower valve manufacturer's instructions for internal adjustment setting. Adjustments should be made to the hottest setting in the shower valve. Additionally the temperature

control of the heater can be lowered to produce a more comfortable hot water temperature.

•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 30-50 psi (2.07-3.45 bar). The use of a pressure reducing valve after the pressure tank is also an effective way to maintain a constant water pressure to the water heater. Watts brand 25AUB- ¾” or N35B-¾” pressure relief valves or equivalent are suggested.

NOISY BURNER / HEATER DURING OPERATION

•CO2 range is out of adjustment. The cover must be in place to confirm CO2 readings. Operating with the cover removed may cause a noisy or unstable burner.

See Chapter 9, CO2 adjustments can only be done by a certified gas technician with a calibrated CO2 analyzer.

Bosch Appliances GWH-635-ES manual Troubleshooting, Unbalanced pressure in water lines