If your Alpha Intec 24X or Alpha Intec 28X boiler is displaying Error 43, the appliance has detected a loss of flame rectification. Although the burner may ignite briefly, the boiler cannot confirm a stable flame, so it shuts down as a safety precaution.

One of the most common causes is a damaged or worn flame sensing electrode. Fortunately, this is usually a straightforward repair when correctly diagnosed by a Gas Safe-registered engineer.

This guide explains what Error 43 means, how the flame rectification system works, common causes, diagnostic procedures, and the recommended repair.

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What Does Error 43 Mean?

The flame rectification system constantly monitors the burner flame.

If the printed circuit board (PCB) cannot detect a flame signal within a specified time, the boiler immediately locks out and displays Error 43.

This prevents unburned gas from entering the combustion chamber and is an essential safety feature.

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How Flame Rectification Works

Many homeowners don’t realise the boiler continuously checks that combustion is taking place.

The flame electrode sends a tiny electrical current through the flame back to the PCB.

If this current disappears, the boiler assumes ignition has failed and immediately shuts the gas valve.

This entire process happens within seconds every time the boiler starts.

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Common Causes of Alpha Error 43

Although the flame electrode is the most common fault, several components can trigger Error 43.

Possible Fault	Likelihood	Recommended Action
Damaged flame sensing electrode	Very Common	Replace electrode
Dirty burner	Common	Clean burner
Loose ignition lead	Common	Inspect connections
Faulty spark generator	Less Common	Test output
PCB fault	Rare	Confirm after other tests
Gas supply problem	Rare	Check inlet pressure

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Symptoms You May Notice

Before Error 43 appears, customers often report:

• Boiler attempts to ignite several times
• Heating stops unexpectedly
• Hot water becomes intermittent
• Clicking sounds during ignition
• Boiler resets temporarily before the fault returns
• Error 43 appearing more frequently over time

Recognising these symptoms early can help prevent a complete heating breakdown.

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Step-by-Step Diagnosis

Step 1 – Inspect the Flame Electrode

Remove the combustion cover and inspect the flame sensing electrode.

Pay particular attention to:

• Cracks
• Carbon deposits
• Incorrect positioning
• Broken ceramic insulation
• Electrode length

The Alpha flame electrode is unusually long and can snap due to repeated heat cycles or accidental damage during servicing.

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Step 2 – Replace the Electrode

If damaged, replace using:

Alpha OEM Part Number: 1258295

Always use genuine manufacturer parts whenever possible.

After installation, ensure the electrode gap and position match the manufacturer’s specifications.

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Step 3 – Check the Ignition Lead

Inspect the ignition cable for:

• Burn marks
• Loose connections
• Damaged insulation
• Moisture ingress

A poor electrical connection can interrupt flame rectification.

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Step 4 – Test Flame Signal

Using the manufacturer’s recommended test procedure, verify that the flame rectification current falls within specification.

Low flame current may indicate:

• Electrode contamination
• Burner contamination
• Earth faults
• PCB issues

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Engineer’s Tip

When replacing the flame electrode, always inspect the burner and combustion chamber simultaneously.

Carbon deposits can affect flame stability and reduce the effectiveness of the new electrode.

Taking an extra few minutes during the repair often prevents repeat call-outs.

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Common Mistakes to Avoid

Avoid these common errors:

• Replacing the PCB before checking the electrode
• Reusing damaged seals
• Ignoring loose earth connections
• Not checking combustion after repair
• Using non-genuine ignition components

Systematic diagnostics always save time.

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Can Homeowners Fix Error 43?

No.

Although the flame electrode appears accessible, it forms part of the combustion system.

Only a Gas Safe registered engineer should remove combustion components or carry out ignition system repairs.

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Preventing Future Error 43 Faults

Regular annual servicing significantly reduces ignition faults.

During a boiler service, engineers should inspect:

• Flame electrode condition
• Burner cleanliness
• Ignition leads
• Combustion readings
• Heat exchanger
• Condensate trap
• Fan operation

Preventative maintenance is considerably cheaper than emergency repairs.

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Why Choose Certificates4UK Ltd?

Since 2011, Certificates4UK Ltd has repaired thousands of domestic boilers throughout Surrey.

We regularly diagnose and repair:

• Alpha
• Worcester Bosch
• Vaillant
• Ideal
• Baxi
• Viessmann
• Vokera
• Glow-worm

Our engineers carry many common ignition components, allowing many repairs to be completed during the first visit.

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Quick Reference

Boiler	Fault Code	Common Cause
Alpha Intec 24X	Error 43	Flame electrode
Alpha Intec 28X	Error 43	Flame electrode
Alpha E-Tec	Ignition fault	Electrode or ignition

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Frequently Asked Questions

Can I reset Error 43?

Resetting the boiler may temporarily clear the fault, but if the underlying problem remains, the error will return.

Is Error 43 dangerous?

The fault itself is a safety shutdown designed to prevent unsafe boiler operation. However, repeated ignition failures should always be investigated by a qualified engineer.

How long does the repair take?

In most cases, replacing a faulty flame sensing electrode takes less than an hour once the fault has been diagnosed.

What is the replacement part number?

Alpha OEM Flame Electrode – Part Number: 1258295

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