Fault Code Lookup

HVAC Sales Master
LED #1 ON / LED #2 ON
Board fault detected (internal control self-check failure)
This code typically points to
  • Internal control self-check failure

Next checks to confirm
  1. Reset control by turning off main power
  2. If state returns after power cycle, replace control

Escalation
Heating blocked
Reset behavior
Main power reset required.
Urgent
Fix now
Source
Lennox ML180UH heating sequence, p.40