Working principle of the appliance
14 Instruction manual BFM
2gis• the Water temperature protection;
• the Flame probe;
• the Pressure switch.
2.4.2 Water temperature protection
By means of the frost, high-limit and safety thermostats, the burner control
monitors three temperatures that are important for safety. The table explains the
working principle of the thermostats with sensors.
Temperature protection
2.4.3 Pressure switch
The pressure switch ensures the discharge of flue gases and the supply of
incoming air during the pre-purge and normal running of the appliance. The
default state of the pressure switch is open. When sufficient pressure difference
is reached, the pressure switch closes. However, in the event of a fault, the
pressure switch is tripped open, and the heating cycle is interrupted. The table
shows the trip point per appliance.
Note
The trip point of the pressure switch is not adjustable.
Pressure switch trip points
2.4.4 Flame probe
To ensure that no gas can flow when there is no combustion, the water heater
is fitted with a flame probe (21). The burner control uses the ionisation-detecting
properties of this probe for flame detection. The burner control closes the gas
valve the instant it determines that there is a gas flow but no flame is present.
Protection Description
Frost thermostat When the frost thermostat sensor (46) measures a temperature of 20°C or
less, the heating cycle (2.3 "The appliance's heating cycle") will start.
High-limit thermostat When the high-limit thermostat sensor (39) measures a temperature higher
than 84°C, the high-limit thermostat will open. The heat demand is terminated
and the burner control halts the heating cycle until the high-limit thermostats
close once more. At that moment the burner control will reset the appliance and
the heating cycle will restart. The high-limit safeguard serves to prevent
overheating and/or excessive formation of scale in the appliance.
Safety thermostat When the safety thermostat sensor (38) measures a temperature higher than
93°C, the safety thermostat will open. The heat demand is terminated and the
burner control will immediately halt the heating cycle. The burner control will go
into a lockout error state. This must be manually reset before the appliance can
resume operation.
Appliance Closing pressure
difference
Opening pressure difference
BFM
30
> 200 Pa < 170 Pa
BFM
50
> 270 Pa < 240 Pa
BFM
80
> 255 Pa < 225 Pa
BFM
100
> 610 Pa < 580 Pa
BFM
120
> 220 Pa < 190 Pa