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fLUE TEMPERATURE PRoBE NTC AND SAfETy THERMAL fUSE
20
fLUE TEMPERATURE PRoBE NTC AND SAfETy
THERMAL fUSE
20.1 function
The Flue temperature probe NTC A in Figure 20.1 and Figure
20.2 senses the temperature of the combustion products that
flow through the condensing heat exchanger.
B
figure 20.1
If the temperature of the combustion products circuit reaches the
limit temperature, the Flue temperature probe NTC reduces the
gas flow rate to the burner. The temperature of the combustion
products should decrease to a safe value temperature.
In the case that the temperature of the combustion products
reaches a potentially dangerous value, it stops the boiler opera-
tion (lock-out).
This allows the use of plastic materials for the flue outlet pipes
and bends.
The use of kits different from the original isn't however allowed,
since the flue pipes are integral parts of the boiler.
C
figure 20.2
A Safety thermal fuse B in Figure 20.1 - Figure 20.2 is also con-
nected in series with the Flue temperature probe NTC and acts
as a safety device in extreme case of incorrect operation of the
Flue temperature control system.
Reaching the breakdown temperature it opens the circuit and
locks out the boiler.
In case of intervention of this safety device the heat exchanger (part
- 40 -
A
A
shown in Figure 20.3) may be damaged and must be replaced.
figure 20.3
20.2 Removal
Warning: isolate the boiler from the mains electrici-
ty supply before removing any covering or compo-
nent.
1 Remove all the case panels and the sealed chamber lid.
2 Disconnect the connector C from the Flue temperature probe
NTC by pressing the plastic hook placed on the side of the
connector.
3 Unscrew and remove the flue temperature probe A (Figure
20.2) from the condensing heat exchanger.
4 Assemble the Flue temperature probe NTC carrying out the
removal operations in reverse sequence.
20.3 Checks
Overheat temperature value
1 Set the temperature control knobs to their max. position and
run the boiler in d.h.w. and c.h.
2 Allow the boiler to reach its maximum operating temperature
(monitor the temperature gauge on the instrument panel).
The boiler should maintain a temperature below that of the
Flue temperature probe NTC and no overheat intervention
should occur.
Temperature-resistance relationship.
1 Remove the Flue temperature probe NTC section "Removal"
page 40).
2 Measure the Flue temperature probe NTC electrical resistance
at the ambient temperature and check it according to the graph
in (Figure 20.4)
12500
12000
11500
11000
10500
10000
9500
9000
8500
8000
7500
7000
6500
6000
5500
5000
4500
4000
3500
3000
2500
2000
1500
1000
500
20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
figure 20.4
°C
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