Instruction manual BFC 15
gis
2.3 Water heater
operating cycle
The temperature sensor T
1
(7) measures the water temperature at the top of the
water heater T
top
). This temperature is sent to the controller. As soon as T
1
is
lower than the set water temperature (T
set
), the controller registers a "heat
demand". The fan (18) starts running and the gas control valve (16) is opened.
The fan runs at full speed and the gas is mixed with the air in the venturi (30).
This mixture is ignited by the hot surface igniter (20) and the water becomes
heated. As soon as the water temperature approaches T
set
the fan rpm drops
to the partial load speed (this is also referred to as modulating). Once T
1
rises
above T
set
, the heat demand ends and the controller stops the operating cycle.
When responding to both the start and end of the heat demand, the controller
assumes a certain margin. We refer to this margin as the
hysteresis (12.2 "
Setting the hysteresis").
2.4 Protection for the
water heater
2.4.1 Introduction
The controller monitors the water temperature and ensures safe combustion.
This takes place using:
• the Protection for the water heater
;
• the Gas control valve;
•the Fan
• the Pressure switch;
• the Flame probe.
2.4.2 Water temperature protection
Using temperature sensors T
1
(7) and T
2
(13), the controller monitors three
temperatures that are important for safety. The table explains the functioning of
the temperature sensors.
Temperature protection
2.4.3 Gas control valve
The controller opens the gas control valve so that gas can be supplied to the
burner. As a safety measure, the gas control valve has two valves. Both valves
shut off the gas supply.
2.4.4 Fan
The fan (18) provides an optimum air supply when there is a heat demand. As
a safety feature, the fan ensures that any gases present in the combustion
chamber are removed, both before and after combustion. We refer to this as
pre- and post-purge.
The fan speed is continuously monitored by the controller (4). The controller
takes control if the fan rpm varies too much from the value set.
Safety Description
Anti-frost
(T
1
< 5°C or T
2
< 5°C)
The frost protection cuts in. The water is heated to 20°C.
Maximum water temperature:
(T
1
> 88°C or T
2
> 88°C)
The high-limit safeguard serves to prevent overheating and/or excessive
formation of scale in the appliance. If the high-limit safeguard is activated,
heating is stopped. This causes the water in the tank to cool down. Once the
water has cooled sufficiently (T
1
< 81°C), the controller resets the appliance.
For extra safety
(T
1
> 93°C or T
2
> 93°C)
A lockout error of the water heater controller takes place. The controller must
be manually reset before the appliance can resume operation (8.3 "Error
conditions"). The reset may only be performed if T
1
< 81°C.
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