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Functions And Maintenance; Operation And Maintenance; Function; Water Temperature Control - Bosch W11B Installation And Operating Instructions Manual

Gas instantaneous water heater
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Operation and maintenance

Sealed parts must not be interfered with.
3. 1


This water heater is fitted with automatic electronic ignition
that provides for easy commissioning.
All that is required is to press the On/Off switch (Fig. 6).
The appliance will then ignite automatically as soon as a
hot water tap is turned on. The pilot flame ignites first and
then, about four seconds later, the main burner; the pilot
flame subsequently goes out after about 20 seconds.
Consequently, the appliance is substantially more
economical because the pilot flame only remains lit until
the main burner ignites, in contrast with conventional
appliances on which the pilot flame remains alight constantly.
After successful ignition, positioning it according to your
output requirement. The further to the left you position the
output control the higher the output, and consequently the
higher the consumption of gas. Maximum output is obtained
when the slide control is to the far left.
In order to optimise energy consumption, adjust slide control
position to supply the minimum output required.
If there is air in the gas pipe when the appliance is
commissioned, this can cause ignition failure. In such cases,
the hot water tap should be turned off and then on again so
that the appliance repeats the ignition cycle. The procedure
should be repeated as necessary until the gas pipe is purged
of air.
Danger: the area in front of the burner can reach very high
temperatures, and there is a risk of burning on contact.

Water temperature control

The water temperature control is used to adjust the water
flow rate, and thereby the water temperature, to the desired
Turning the control clockwise reduces the water flow rate
and increases the temperature; turning the control anti-
clockwise increases the water flow rate and reduces the
If the temperature is set only as high as required, energy
consumption is reduced and the likelihood of scale deposits
in the heat exchanger minimised.

Appliance adjustments

All instantaneous water heaters are factory-adjusted and
require no further adjustment.*
Water heaters that use LPG (liquefied petroleum gas, i.e.
butane/propane) are set to the operating pressure stated
on the identification plate (28 mbar).
Natural gas appliances are set to a Wobbe Index of 15 kWh/
and a supply pressure of 20 mbar.
* Sealed components must not be tampered with.


The appliance should only be serviced by an approved
A complete overhaul should be carried out after two years.
The overhaul should involve thoroughly cleaning the heat
exchanger, burner, pilot burner and automatic water valve
If necessary, the inside of the heat exchanger and the
connecting pipes should be descaled.
Check the gas and water valves for leaks and carry out a
complete function check.
If components need to be replaced, use only genuine Bosch
spare parts.

Flue gas safety device

The recommition must be done from a qualified technician
The flue gas safety device must not under any circumstances
be switched off, simulated or replaced by any other
Operation and safety precautions
The flue gas safety device checks the effectiveness of flue
gas extraction by the flue. If it is inadequate, the appliance
switches off automatically so that the combustion fumes do
not escape into the room in which the appliance has been
installed. The flue gas safety device resets after a cooling-
down period.
If the appliance shuts down while in operation, ventilate the
room. Wait about 10 minutes then restart the appliance. If
the problem recurs, call an engineer. The user must never
make any modifications to the appliance.
If faults occur on the flue gas safety device, proceed as
- Undo flue gas safety device fixing screw.
- Unplug igniter unit connector
Replace damaged component with new one and refit using
the reverse of the procedure set out in the table above.
Function check*
Flue gas safety device function check:
- Disconnect flue pipe
- Replace with pipe (about 50 cm long) with sealed end
- Fit pipe vertically
- Start up appliance at rated output and set temperature
control to maximum temperature.
Under those conditions, the appliance should shut down
after two minutes. Remove temporary pipe and reconnect
flue pipe.
* This work may only be carried out by an approved engineer.

Converting to a different gas type

Use only the genuine Bosch conversion kit. Conversion
may only be carried out by an approved technician.
6 720 607 527

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