A2 Ignition Failure And Reignition Sequence - Bosch BGH96 Troubleshooting Manual

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