Bosch BGH96 - High Fire Heating Mode Logic (W1+W2 Signal)

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Bosch 96% AFUE Gas Furnace Troubleshooting Guide
01.2019 | BTC 770502101 AData subject to change
A1.2 High Fire Heating Mode Logic (W1+W2 Signal):
Figure 25
1
When there is a call for heat (W1), the inducer will start on HIGH
speed and the low pressure switch closes. This will last for 15s.
2
Inducer will turn to low speed and ignitor will energize. This
preheating sequence lasts for 17s.
3
After preheating, gas valve opens and the burners light. The ignitor
will turn off after 3s.
4
Before gas valve, inducer, pressure switch turn to high stage, there
is a 5s delay.
4
+
5
There is a time delay of 30s before blower motor starts.
6
The system is working properly in high stage.
7
When there is no call for heat, there is a time delay before inducer
shuts down. This will last for 15s.
8
The blower motor will run at high speed for 30s for fan delay.
9
There is a fan delay to dissipate heat in the system. This time
depends on the dip switch S1-3 & S1-4. The default time is 180s.