Bosch Appliances GWH-635-ES

6 720 607 072

Troubleshooting

•Cold water is mixing with the hot water outlet

(crossover)

Test by following 4th bullet under BURNERS D O

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 re quires 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 wa ter

flow ra te 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 WAT ER 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 p ressure 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 t emperature

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

• CO

range is out of adjustment. The cover must be

in place to confirm CO

readings. Operating with the

cover removed may cause a noisy or unstable burner.

See Chapter 9, CO

adjustments can only be done

by a certified gas technician with a calibrated CO

analyzer.