Safety Notice

This guide is strictly for Gas Safe-registered engineers.
Only qualified professionals with the correct testing equipment may perform CO₂ adjustment and flue gas analysis on Main Eco Elite boilers.

Tampering with a gas boiler without Gas Safe registration is both dangerous and illegal under UK regulations.

Common CO₂ Drift Issue

Field testing has shown that Main Eco Elite boilers, particularly those with larger heat exchangers, can experience CO₂ drift over time.
When this occurs, combustion readings become inaccurate, leading to reduced efficiency, poor performance, and potential safety concerns.

Regular flue gas analysis and recalibration help maintain optimal combustion and ensure safe operation.

Tools Required

• Calibrated Flue Gas Analyser
• 2.5 mm hex key (for maximum CO₂ adjustment)
• 4 mm hex key (for minimum CO₂ adjustment)

Step-by-Step CO₂ Adjustment Procedure

️ Always perform this procedure with a calibrated analyser and in accordance with manufacturer and Gas Safe standards.

1. Enter Max Mode

To activate full burn for testing:

• Turn the control dial to RESET (position 6).
• Wait until “SERV” appears on the display.
• Turn the dial back to the dot (home position) within 2 seconds.

This sequence enables Max Mode, forcing the boiler to operate at maximum output for accurate analysis.
(This method is the same as used for Baxi Duo-Tec boilers.)

2. Insert Flue Gas Analyser

• Insert the analyser probe into the test port located on the flue terminal.
• Allow readings to stabilise before making adjustments.

3. Adjust Max CO₂

• Use a 2.5 mm hex key to carefully adjust the gas valve throttle.
• Target readings:
  • 25 kW model: CO₂ = 9.0%
  • 30 kW model: CO₂ = 9.1%

️ Adjust gradually — small movements have a significant impact on readings.

4. Adjust Min CO₂

• Remove the protective cap and use a 4 mm hex key to access the minimum setting.
• Adjust until the CO₂ reading reaches 8.4%.

5. Recheck Max CO₂

If the minimum setting has been altered, retest the maximum to ensure both parameters remain balanced.
Always allow time for readings to stabilise before final confirmation.

Engineer’s Reminder

All internal boiler adjustments must be carried out by Gas Safe-registered engineers only.
Unqualified work can cause gas leaks, carbon monoxide exposure, and invalidate manufacturer warranties and insurance coverage.

For homeowners and landlords across Surrey and London, always book a professional engineer through Certificates4UK Ltd for:

• Boiler servicing and fault diagnostics
• Gas Safety Certificates (CP12)
• EICR and EPC compliance

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