3.2.3 Safety devices
Safety temperature limiter (eSTL)
The fuel supply is shut off and the fan and the pump run-on are activated if the tem-
perature on the eSTL exceeds a value of 95 °C (
W12
). The boiler restarts automatically,
if the temperature drops below the flow setpoint value for 1 minute.
The fuel supply is shut off and the fan and the pump run-on are activated if the tem-
perature on the eSTL exceeds 105 °C. The installation goes to lockout (
F11
).
Temperature differential supply/return
If the difference between flow and return temperature exceeds the value of parameter
A21, the boiler is switched off (
W15
). The installation goes to lockout after 30 warnings
with (
F15
). When approaching this value, first the pump rating is increased to 100
%, then the burner rating is reduced step by step.
Temperature differential eSTB/supply sensor
If the difference between eSTB and supply temperature exceed the value of parameter
A22, the boiler is switched off (
W18
). The installation goes to lockout after 30 warnings
with (
F18
).
Monitoring supply temperature increase (gradient)
If the temperature at the eSTL increases too rapidly (parameter A23), the boiler is
switched off (
W14
). This function is only activated at a temperature of > 45 °C.
Flue gas sensor
The fuel supply will be switched off if the flue gas temperature exceeds the value
defined in parameter
33
(factory setting 120 °C). The fan and pump run-on is acti-
vated (
W16
).
Air pressure switch
The air pressure switch monitors the fan pressure. Before the pre-purge phase is
started, the idle position of the switch contact is checked. During the pre-purge phase
the fan rotation is checked. The system goes to lockout after 4 failed start attempts
(
F32
,
F45
).
Flue gas pressure switch
During operation, the pressure in the condensate collector is monitored. This stops
the siphon from being squeezed empty if the backpressure is too high. If the pressure
switch is activated (>5.5 mbar) the system goes to lockout (
F46
). If the pressure
switch is activated during the idle time of the fan the system also goes to lockout
(
F38
).
Water level interlock
If the system pressure drops below 1 bar, the boiler switches off (
F36
). If the pressure
increases to 1.2 bar again, the boiler automatically restarts.
Gas pressure switch
The gas connection pressure is monitored both before and during operation. If the
gas pressure set is not maintained, the boiler switches off (
W47
).
Installation and operating instruction
Gas condensing boiler WTC-GB 90-A
3 Product description
83266502 • 1/2010-08 • La
13-95
