Bosch BGH96 - Low Fire Heating Mode Logic (W1 Signal)

Troubleshooting Guide Bosch 96% AFUE Gas Furnace | 23
BTC 770502101 A | 01.2019
Data subject to change
A1 Heating Modes
A1.1 Low Fire Heating Mode Logic (only W1 signal):
Figure 24
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
There is 30s time delay before blower motor starts.
5
The system is working properly.
6
When there is no call for heat (no W1 call) and no fl ame is sensed,
post-purge begins. This will last for 15s.
7
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.