Bosch BGH96 - Ignition Failure and Reignition Sequence

Troubleshooting Guide Bosch 96% AFUE Gas Furnace | 25
BTC 770502101 A | 01.2019
Data subject to change
A2 Ignition Failure and Reignition Sequence
If the furnace fails to ignite, there is a separate logic for the re-ignition
sequence:
Figure 26
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
The gas valve will open for 4s if there is no fl ame.
5
The inducer will run at high speed for 60s.
6
Test of low pressure switch.
7
Preheating occurs for 27s.
8
After preheating, gas valve opens. The ignitor will turn off after 3s.
After two failed ignition attempts, system will lock out.