These are all the reasons the service manual lists for #2 blinking light:
1. Vacuum
Loss of vacuum may be causes by:
a. Operator error or neglect
􀂉 Leaving the Main Door open too long
􀂉 Forgetting to close the Main Door
􀂉 Leaving the Ashpan Door open too long
􀂉 Forgetting to close the Ashpan Door
􀂉 Allowing the Chimney to get plugged.
􀂉 Allowing the Ash Traps to get plugged.
If an owner calls in with a #2 diagnostic light flashing, first cover all items listed that may be caused by incorrect operation of the stove. Quiz the owner about their habits in regards to the Periodic maintenance. If they have been lax in cleaning the Ash Traps (See Figure 21 on Page 48) and venting system, have them first clean their stove and try it again.
b. Component Failure. Which components may be the cause?
􀂉 Combustion Fan
􀂉 Vacuum switch
􀂉 Control Board
􀂉 Vacuum hose
􀂉 Wiring harness
􀂉 Wiring connections
The component list dealing with Vacuum problems will need a closer look. Check the simplest item first.
• Check to see if the combustion Fan comes on.
􀀹 If the combustion Fan isn’t running, check the wiring connections at the fan.
ô€€¹ Check the wiring connections on the opposite end at the Terminal Block (white wire) and at the Molex connector (Blue wire) that plugs into the control board. They may look OK, but in fact may not be making contact the pins from the control board.
ô€€¹ Check both wires in the harness for continuity if needed with an OHM meter. (White and Blue wire)
􀀹 Check for voltage at the fan, if voltage is present and the fan isn’t running replace the combustion fan.
• Check the control board.
ô€€¹ Check for voltage at the pin out for the Blue wire at the control board. If no voltage is present replace the control board.
• Check all wiring connections related to the Vacuum system first.
ô€€¹ Check the 2 Gray wires that are plugged into the vacuum switch.
ô€€¹ If the wires are plugged in, check the opposite ends that are plugged into the control board. Make sure the wires a fully pushed into the Molex connector that plugs into the control board. They may look OK, but in fact may not be making contact the pins from the control board.
ô€€¹ Check the Gray wires for continuity if needed with an OHM meter.
• If all wires and connections are correct, check the vacuum switch.
ô€€¹ Unplug the 2 Gray wires and jump them together. Run the stove and see if that corrected the problem.
􀀹 If the stoves runs, check the vacuum reading in the stove using a manometer connected to the vacuum hose. Be sure to leave the 2 Gray wires jumped together or the stove will shut down again. The vacuum should be at least .05†WC negative pressure. The stove typically has a reading of between .1†and .25†WC negative pressure.
ô€€¹ If the vacuum reading is relatively low, check the intake air damper to see if it is wide open. Adjusting the damper to a position that is more closed will increase the Vacuum reading.
If dealing with an intermittent problem most likely it will be a problem in the wiring system related to a faulty connection or possibly a combustion fan that is getting too hot and the Thermal Override is shutting it down. This would likely be seen when the stove is running on the higher settings and the combustion fan should be check immediately after the stove shuts down. Once the fan cools down it may start running again.
http://www.eventempinc.com/stcroix/downloads/dig2/Digital_Control_Board_Service_Manual.pdf