Flame Failure Device Not Working: Production-Line Causes and Fixes

What the FFD Actually Does

The FFD is a safety interlock: gas is allowed to flow only when a flame is proven. When the operator presses and turns the knob, gas flows and is ignited; the sensor must confirm the flame within the opening time, after which the valve stays open. If the flame is blown out, the sensor loses the signal and the valve must close within the closing time. Two sensor technologies are used — a thermocouple that generates a small voltage from heat, and an ionisation (flame-rectification) electrode that senses current through the flame. Most “FFD not working” faults trace back to how these are installed and connected, which is covered in the comparison in F7: thermocouple vs ionisation.

Symptom 1: Gas Cuts Off When the Knob Is Released

Symptom 2: Gas Does Not Close When the Flame Is Out

Flame Rectification: Why an Ionisation FFD “Sees” a Flame

An ionisation FFD relies on flame rectification: a flame conducts current better in one direction, so an AC-driven controller applies a voltage to the sensing electrode and reads a small rectified DC current only when the flame bridges the electrode to the burner. That is why the burner must be properly grounded and the electrode must be in the flame — without a clean ground path the controller cannot see the current and the valve closes. A damp, sooted or mispositioned electrode, a loose ground, or a controller mismatched to the burner are the most common line causes for an ionisation FFD that intermittently cuts out. Because the same symptom can also come from a lifting flame, check combustion and air adjustment first, as described in F3: yellow tip vs blue flame, before replacing the controller.

Testing the FFD on the Production Line

1. Ignite the burner and record the opening time until the valve holds without the knob (must be within 10 s for GB);
2. Extinguish the flame and record the closing time until gas is cut (must be within 60 s for GB);
3. Confirm the valve physically closes and no gas passes after cut-off, using the gas-tightness check in A4: gas tightness and flame failure;
4. Repeat for every burner, and log the times against the serial number.

These are objective, timed measurements — an operator watching a flame cannot reliably judge a 60-second limit or a slow valve. A gas cooker test bench automates ignition, extinguishes the flame, times the open and close, verifies the downstream shut-off, and fails the unit if any burner is outside the limit. The FFD test should be interlocked with the gas-leak test (F2) so a unit that cannot prove its flame or its shut-off cannot pass the line.

A Fault-Finding Flow

• Will not hold open: check the flame is on the sensor, then the connection, then the valve coil (see F6: gas valve failure);
• Will not close: check the valve is not stuck and the sensor/controller is not shorted or bypassed;
• Intermittent: check ground, moisture, sooting and flame stability before replacing parts;
• Multiple units fail: check the assembly jig position for the sensor and the incoming component batch, not each appliance in isolation.

Logging the FFD times for every serial number also turns the safety test into a quality tool. When opening or closing times drift slowly across a shift — a few seconds slower, but still within the limit — the stored data shows the trend before units start failing, which usually points to a worn jig, a loosening fixture or a changing component batch rather than to individual workmanship. A line that only records a pass/fail mark cannot see this drift and is instead surprised by a sudden batch of failures. Keeping the actual timed values, together with the component batch and operator, lets engineering trace a field complaint to the exact point of manufacture and confirm whether a returned appliance passed or missed its FFD sequence, which is the evidence an importer and an authority will ask for.

Common Mistakes

• Sampling the FFD instead of testing every burner on every unit;
• Bridging or taping the FFD to “keep the line running” (creates a direct safety hazard);
• Replacing the controller when the real cause is a mispositioned sensor or a lifting flame;
• Judging timing by eye instead of recording open/close seconds;
• Not verifying the valve actually seals after cut-off;
• Ignoring a batch drift in sensor position caused by the assembly jig.