Thermal Protections; Pressure Switch; Description Of The Control Board - SBM AMC 12 Installers And Users Instructions

4.5 Thermal protections

4.5.1 Protection of the exchanger
 The thermal protection of the exchanger is done by 2 CTN temperature probes set on the
exchanger of the unit.
In case of overheating of the exchanger, in a first time, the speed of the main fan will increase and
in a second time, the capacity of the burner will be limited at its minimum. In case of abnormal
overheating, the electric supply of the premix system will be closed. When the exchanger is cold
enough, the heat cycle restart (the display shows alternatively E and 1).
If the overheating continue (defective electrical supply cutting), the control board is going to a
safety state (the display on the board shows alternatively A and 2 and the MULTITHERM shows
the code 2).
After controlling and fixing, the control board shall be reset directly by pressing the button on the
control board or by the menu of the MULTITHERM (see the technical instructions).
4.5.2 Protection of the exhaust gases pipe
 For a use of plastic exhaust gases pipes on the warm air heaters, a sensor controls the exhaust
gases temperature (T < 120°C). When the exhaust gases temperature is too high (T > 110°C), the
burner decrease its power to the minimum.
Nevertheless the temperature increases and reaches 115°C, the burner stops. When, after a re-
ignition, the situation is the same, the heater is locked
(the safety board shows alternatively A and 7).

4.6 Pressure switch

The appliance is equipped with a pressure switch in order to control the combustion air flow through
the heat exchanger.
During the pre-ventilation step, the difference of pressure between inside and outside the exchanger is
measured.
If the difference of pressures is too weak, the display on the control board shows alternatively A and 9
which means a pressure drop in the heat exchanger which have to be checked.

4.7 Description of the control board

The control board controls all the functions of the AM heater and communicates with the thermostat
MULTITHERM.
The control board integrates the following functions :
- ModBus communication system with the MULTITHERM
- Ignition of the burner by sparks
- Flame detection by ionisation
- Modulation of the gas valve opening
- Modulation of the premix fan with information return
- Modulation of the main fan
- Heat protection of the exchanger (2 CTN sensors)
- Control of the ambiant temperature (CTN sensor)
- LED signals of the heater: heat demand (green LED) and safety state (red LED)
- Display of the heater state on the 8 segments screen
- Reset button
- Service mode function
- Recognition system of the appliance
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