If you’re experiencing Ideal Logic intermittent hot water, you’re not alone. One of the most common faults affecting Ideal Logic and Ideal Logic+ boilers is a worn or faulty flow turbine, often accompanied by a Hall sensor issue.

Customers typically report that the hot water works one minute and runs cold the next. Because the fault is intermittent, it can be frustrating to diagnose without a systematic approach.

At Certificates4UK Ltd, we’ve repaired hundreds of Ideal boilers throughout West Molesey, Esher, Walton-on-Thames, Thames Ditton, Weybridge, Cobham, Surbiton, Kingston upon Thames, and surrounding Surrey areas. This guide explains how Gas Safe engineers diagnose and repair one of the most common domestic hot water faults on Ideal Logic boilers.

What Causes Intermittent Hot Water?

When you open a hot tap, the boiler must detect water flow before ignition begins.

The flow turbine spins as water passes through it, while the Hall sensor detects this movement and sends a signal to the PCB.

If either component fails, the boiler may not recognise that hot water is being requested, preventing ignition.

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Common Symptoms of Ideal Logic Intermittent Hot Water

You may notice:

• Hot water randomly turning cold.
• Boiler sometimes fires, sometimes doesn’t.
• No fault code displayed.
• Boiler fails to recognise hot water demand.
• Boiler works normally after repeated attempts.
• Hot water operates inconsistently throughout the day.

These symptoms almost always point towards the flow turbine or Hall sensor rather than the burner or gas valve.

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Components Involved

The domestic hot water detection system consists of:

• Flow turbine
• Hall sensor
• Brass turbine housing
• PCB
• Cold water inlet assembly

Each component plays an important role in detecting water flow.

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Tools Required

Professional diagnosis requires:

• Digital multi meter
• Magnet
• 18 mm spanner
• Adjustable grips (if required)
• Silicone lubricant
• Replacement flow turbine

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Step 1 – Confirm the Customer Complaint

Begin by asking the customer exactly what happens.

Typical comments include:

“Sometimes I get hot water.”

“It starts hot then suddenly goes cold.”

“Sometimes the boiler doesn’t even fire.”

Intermittent faults provide valuable clues before dismantling the appliance.

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Step 2 – Remove the Boiler Front Cover

Following manufacturer instructions:

• Isolate the electrical supply.
• Remove the front casing.
• Restore power safely.
• Run a hot tap.

Observe whether the boiler attempts ignition.

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Step 3 – Locate the Flow Turbine

The flow turbine is located behind the condensate trap.

You’ll find:

• Brass valve body
• Plastic flow turbine
• Hall sensor clipped to the housing

This is where most intermittent hot water faults originate.

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Step 4 – Check the Hall Sensor

Observe the Hall sensor LED.

A healthy Hall sensor should display a steady red light.

If the light:

✅ Remains steady – Continue diagnosis.

❌ Flickers or doesn’t illuminate – Suspect a faulty turbine or Hall sensor.

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Engineer’s Tip

One of the quickest checks involves using a magnet.

Pass a small magnet past the Hall sensor.

If functioning correctly, the Hall sensor should simulate water flow and request hot water from the PCB.

This simple test can save valuable diagnostic time.

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Step 5 – Isolate the Cold Water Supply

Before removing the turbine:

• Turn off the cold mains supply.
• If the internal isolation valve leaks, isolate the property at the main stop tap.
• Open a hot tap until the system depressurises.

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Step 6 – Remove the Flow Turbine

Remove the Hall sensor first.

Using an 18 mm spanner:

• Unscrew the flow turbine.
• Carefully inspect for wear.
• Check for damaged seals.
• Examine the impeller.

A worn impeller often causes intermittent detection.

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Step 7 – Install the New Flow Turbine

Before fitting the replacement:

• Lubricate the rubber seal.
• Tighten securely.
• Refit the Hall sensor.
• Restore the water supply.
• Test multiple hot water demands.

The boiler should now respond immediately whenever a hot tap is opened.

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Why Flow Turbines Fail

Flow turbines are mechanical components and naturally wear over time.

Common causes include:

• Hard water deposits
• Debris in the water supply
• Worn impeller
• Damaged internal magnet
• Seal deterioration

Fortunately, replacement is usually straightforward for a qualified engineer.

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Other Causes of Intermittent Hot Water

Although the flow turbine is a common cause, similar symptoms may also result from:

Symptom	Possible Cause
Boiler doesn’t recognise tap	Flow turbine
No Hall sensor LED	Hall sensor
Boiler fires then stops	Plate heat exchanger
Weak hot water	Flow restrictor
Hot then cold	Diverter valve
No ignition	PCB fault

A structured diagnosis ensures the correct component is replaced.

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Why Professional Diagnosis Matters

Intermittent faults can be difficult to identify without experience.

Professional diagnosis helps:

• Avoid unnecessary replacement parts.
• Reduce labour time.
• Restore reliable hot water.
• Prevent repeat call-outs.
• Improve customer satisfaction.

At Certificates4UK Ltd, every repair begins with systematic fault finding—not guesswork.

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Why Choose Certificates4UK Ltd?

Established in 2011, Certificates4UK Ltd provides expert boiler diagnostics, servicing, and repairs across Surrey.

Our experienced Gas Safe engineers repair:

• Ideal
• Worcester Bosch
• Vaillant
• Baxi
• Alpha
• Viessmann
• Vokera

We also provide:

• Boiler servicing
• Boiler installations
• Boiler repairs
• Landlord Gas Safety Certificates (CP12)
• Electrical Installation Condition Reports (EICRs)
• Energy Performance Certificates (EPCs)

Whether you’re in West Molesey, Walton-on-Thames, Esher, Thames Ditton, Hersham, Cobham, Weybridge, Kingston upon Thames, or elsewhere in Surrey, we’re here to help.

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Frequently Asked Questions

Why does my Ideal Logic boiler only produce hot water sometimes?

The most common cause is a worn flow turbine or faulty Hall sensor that intermittently fails to detect water flow.

Can the Hall sensor be tested?

Yes. A Gas Safe engineer can test the Hall sensor using diagnostic methods, including a simple magnet test to confirm whether it is sending the correct signal.

Is replacing a flow turbine expensive?

Flow turbines are generally an affordable replacement part, but accurate diagnosis is essential to avoid replacing components unnecessarily.

Can homeowners replace a flow turbine?

No. Accessing internal boiler components should only be carried out by a qualified Gas Safe registered engineer.

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