A1 Heating Modes; A1.1 Low Fire Heating Mode Logic (Only W1 Signal) - Bosch BGH96 Troubleshooting Manual

Troubleshooting Guide
A1 Heating Modes

A1.1 Low Fire Heating Mode Logic (only W1 signal):

Figure 24
When there is a call for heat (W1), the inducer will start on HIGH
1
speed and the low pressure switch closes. This will last for 15s.
Inducer will turn to low speed and ignitor will energize. This
2
preheating sequence lasts for 17s.
After preheating, gas valve opens and the burners light. The ignitor
3
will turn off after 3s.
4 There is 30s time delay before blower motor starts.
5
The system is working properly.
When there is no call for heat (no W1 call) and no fl ame is sensed,
6
post-purge begins. This will last for 15s.
There is a fan delay to dissipate heat in the system. This time
7
depends on the dip switch S1-3 & S1-4. The default time is 180s.
BTC 770502101 A | 01.2019
Bosch 96% AFUE Gas Furnace | 23
Data subject to change