Flame signal too low or flame loss

What is going on

The control reads the flame signal in parameter 8.7.9. It needs a signal above 18 to detect flame at start, and it calls a flame loss if the signal falls below 15. The gap between those two numbers is your margin. A signal that barely clears 18 and sags during the run is the early warning before the boiler starts locking out.

Likely causes

• Weak or dirty flame sensing, such as a fouled or worn sensor rod
• Low gas supply or incorrect gas setup
• Ignition power set incorrectly (parameter 2.2.0)
• Poor burner condition or bad flame pattern
• Loose or damaged sensor wiring

Check in this order

1. Open the complete menu and read the flame signal at parameter 8.7.9 while the burner runs.
2. Confirm the signal rises above 18 at ignition, since the control will not accept the flame otherwise.
3. If the signal drops below 15 during operation, check the flame sensor and burner condition.
4. Inspect the sensor rod and clean light deposits, and check its wire and connector for looseness or damage.
5. Check that the ignition power in 2.2.0 matches Table 33 for the gas and PCB in use.
6. Confirm gas supply pressure and fuel setup match the rating plate, and verify combustion with an analyzer.
7. Gas and combustion work belongs to a licensed technician.

More boiler guides

• Access the low voltage wiring connections
• Blocking errors versus lockout errors
• Blower not running
• Blower runs at high speed with burner off
• Boiler bangs or hisses; Lockout 81 delta T
• Burner not running on a call for heat