FCS System Found Melted Near the Air Intake

Technical Analysis of Possible Causes and Corrective Actions

Regarding the issue encountered on a pellet appliance, where the FCS system was found melted near the air intake, the analysis of the information provided by the technician on site allows identifying some possible causes related to critical issues in the combustion air intake circuit.

The presence of unburned pellets in the brazier (or ash drawer), combined with the perception that the appliance draws air from unintended points, highly suggests an anomaly in the air/smoke circuit.

In particular, it is hypothesized that there may be a return of hot air coming from pellets not completely combusted in the intake duct. Considering that these appliances operate under negative pressure, any leak or imperfect sealing of the circuit can significantly alter the combustion balance, generating abnormal thermal conditions.

Hypothesized Technical Dynamics

Under correct installation and perfect sealing conditions, the system operates ensuring:

• Controlled aspiration of combustion air
• Proper evacuation of fumes
• Stability of the air/pellet ratio

If infiltrations or draft imbalances occur, the following may develop:

• Unstable or poor combustion
• Accumulation of unburned pellets
• Localized temperature increases
• Thermal returns along the intake circuit

These conditions can subject sensitive components such as the FCS system to thermal stress, up to damage by melting.

Possible Causes

1️⃣ Uncontrolled Air Infiltrations

• Worn, damaged, or improperly positioned gaskets (door, ash drawer, fittings).
• Leaks or imperfect airtight seals along the coaxial duct (estimated length 5–6 m).
• Combustion air connection not perfectly sealed.
• Microcracks or non-compliant joints.

Technical effect: alteration of the negative pressure regime and destabilization of the combustion air flow.

2️⃣ Incorrect Draft

• Length of the coaxial duct with the presence of critical bends.
• Partial obstructions (soot, ash, foreign objects).
• Installation not compliant with manufacturer specifications.
• External terminals unsuitable or exposed to unfavorable environmental conditions.

Technical effect: pressure variations and possible localized flow reversal.

3️⃣ Non-Optimal Combustion

• Air/pellet parameters not properly calibrated.
• Pellets with unsuitable quality characteristics (high moisture, high ash content).
• Partially obstructed or underperforming smoke fan.
• Brazier with partially clogged holes.

Key indicator: presence of unburned pellets in the brazier, a typical sign of unstable combustion.

Recommended Actions for the CAT

✔ Complete check of the air circuit sealing

• Inspection of all possible air intakes along the appliance.
• Verification of the condition and correct installation of gaskets.
• Check of airtight closure of door and ash drawer.
• Confirmation of perfect sealing of the combustion air circuit.

✔ Duct inspection 

 

• Check for the presence of narrowings or penalizing bends.
• Inspection for any internal obstructions.
• Verification of installation compliance with manufacturer specifications.

✔ Combustion optimization

• Thorough cleaning of the brazier and air passages.
• Inspection and cleaning of the smoke fan.
• Recalibration of combustion parameters.
• Verification of the quality of the pellet used.
• Possible functional test with certified pellet.

Concluding Considerations

The melting of the FCS system near the air intake should not be interpreted as the primary cause of the problem, but rather as a consequence of an imbalance in the air/smoke system.

In pellet generators operating under negative pressure, correct sealing of the circuit and balance between aspiration and combustion are essential conditions for:

• Operational safety
• Flame stability
• Component durability

A methodical and complete analysis of the entire circuit usually allows identifying the primary cause and preventing the recurrence of the issue.