Why doesn't the gas-fired boiler ignite despite running burner motor and voltage at controller?

If the burner motor of a gas-fired boiler is running and voltage is present at the controller terminal, but there is no ignition followed by a system failure and stop, this situation can be attributed to several potential issues. Here's a breakdown of what might be happening and what to check:

Ignition System Failure: The ignition system, which may include spark electrodes or an igniter, could be faulty. Check for any signs of damage, misalignment, or dirt on the igniter or electrodes.

Control Board or Ignition Controller Issues: The control board or ignition controller may be malfunctioning. These components control the sequence of operations in the boiler, including ignition. If they fail, the ignition process won’t initiate correctly.

Gas Supply Problems: If there is an issue with the gas supply (like low pressure, no gas flow, or closed valves), the burner will not ignite. Ensure that the gas supply is consistent and meets the required pressure specifications.

Safety Lockout: Modern boilers have several safety mechanisms. If the boiler attempted to ignite several times unsuccessfully, it might enter a safety lockout mode, preventing further attempts. This could be due to issues with the ignition system, gas supply, or other safety-related concerns.

Faulty Flame Sensor: If the flame sensor is dirty or faulty, it may not detect the flame correctly, leading the system to shut down shortly after an attempted ignition.

Airflow Issues: Adequate airflow is necessary for combustion. If vents or air intakes are blocked, or if the exhaust flue is obstructed, it can prevent ignition.

Electrical Connections and Wiring: Loose or damaged wiring can affect the ignition system. Check for any loose connections or signs of electrical faults.

Blocked Burner: A dirty or blocked burner can prevent proper gas flow and ignition. Regular cleaning and maintenance are required to keep the burner in good working condition.

Pressure Switches: Pressure switches monitor the boiler's internal pressure and the venting pressure. If these switches are not functioning correctly or if the pressures are outside of the specified ranges, the ignition process might be halted.

Thermostat Setting: Ensure the thermostat is set correctly. If the temperature setting is too low, the boiler might not ignite.

Overheating Protection: If the boiler has overheated in the past, an overheating protection device might have tripped, requiring a reset or technical inspection.

Given the complexity of gas-fired boilers and the potential safety hazards associated with gas and electrical systems, it's advisable to seek assistance from a qualified technician to diagnose and resolve the issue. They have the expertise to safely identify and fix the problem, ensuring the boiler operates efficiently and safely.