E.C.A. Fortius Service Manual page 25

DIFFERENTIAL AIR PRESSSURE SWITCH (APS)
17
Differential air pressure switch is used in room sealed fan assisted models. It controls the air flow
by measuring the pressure differences of the clean air required for burning and flue gas. In case of
problems like blockage in the air/flue kit or a strong outer air flow, the air pressure switch shuts
down the boiler. The low pressure inlet of the differential air pressure switch is connected to the fan
with a silicon hose. The high pressure inlet is connected to the combustion body again with a silicon
hose.
When the boiler is started, the differential air pressure switch is already open. The fan operates, and
after a certain period of time, when the pressure difference is above the predefined value the switch
closes and the boiler begins operating. When the pressure difference is under certain value, the
switch opens and prevents the operating of boiler.
The electric circuit of the differential air pressure switch is connected to terminals (1) and (3) (2 not
connected).
Table 16 Differential Air Pressure Switch
Interior diameter of silicon hose to fan
Interior diameter of silicon hose to combustion body
Low pressure inlet (P2)
High pressure inlet (P1)
TTB TEMPERATURE SENSOR
18
The TTB temperature sensor is an NTC sensor like the central heating and domestic water
temperature sensors. The R-T relation of the sensor is shown in Table 17.
TTB temperature sensor measures the temperature of the flue gas in open flued boilers. If the flue
gas temperature exceeds the limit value because of blockage in the flue system or insufficient
chimney draught, the TTB sensor shuts down the boiler by sending a signal to the main board and
the boiler can not be started for 15 minutes. The TTB temperature sensor is mounted to hood using
two screws.
The TTB temperature sensor limit value differs according to operating capacity.
a) In the first 90 sec., TTB sensor limit temperature is 100°C.
b) After the 90 sec. of start up period, the limit temperature is between 75 - 95 °C depending on the
boiler capacity.
fig. 16 Differential Air Pressure Switch
5 mm
5 mm
24