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The Worcester E5 218 error code usually points to a problem with the boiler's flow temperature sensor. This sensor monitors the temperature of the water leaving the boiler. If it detects readings outside its expected range, the boiler will lock out to protect itself from damage.

Although the fault isn't usually dangerous, you should avoid repeatedly resetting the boiler until the cause has been found.

How-to-fix-the-Worcester-Bosch-E5-218-Error
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What does the Worcester E5 218 error code mean?

The flow temperature sensor (NTC thermistor) measures the temperature of the water circulating through the heating system. It sends resistance readings to the printed circuit board (PCB), which converts them into temperature values.

If the readings become inaccurate or inconsistent, the boiler displays the E5 218 fault code and shuts down.

Why does the E5 218 fault happen?

Limescale affecting the flow temperature sensor

Limescale is one of the most common causes of this fault, particularly in hard water areas.

Deposits can build up around the sensor and affect the temperature readings. The boiler may then believe the water is overheating, even when it isn't.

Limescale can also reduce heating efficiency and increase wear on other internal components.

Faulty flow temperature sensor

The sensor itself may fail over time through normal wear. A Gas Safe engineer can test the thermistor with a multimeter and replace it if necessary.

Damaged wiring or electrical connections

Loose, damaged or corroded wiring between the sensor and PCB can also produce incorrect readings and trigger the E5 218 fault.

What happens if the boiler overheats?

If the boiler genuinely overheats, excessive temperatures can place additional stress on the heat exchanger and other internal parts.

Modern Worcester Bosch boilers include safety lockout features to prevent further damage. Even so, it's best to leave the boiler switched off until the fault has been diagnosed.

Can you reset an E5 218 fault?

Occasionally, a reset may clear the fault if it was caused by a temporary interruption.

However, if the error returns, avoid repeatedly resetting the boiler. Continuing to run it without fixing the underlying problem can lead to more expensive repairs.

Instead, arrange for a Gas Safe engineer to inspect the boiler.

How a Gas Safe engineer fixes an E5 218 fault

The engineer will typically:

  • Test the flow temperature sensor.
  • Check the sensor wiring and electrical connections.
  • Inspect for limescale or circulation issues.
  • Replace faulty components where required.
  • Reset and test the boiler after repairs.

How to help prevent the E5 218 error

Regular servicing helps identify worn sensors, wiring problems and system contamination before they cause a breakdown.

In hard water areas, reducing limescale build-up with suitable water treatment can also help protect the heating system.

If you're seeing several Worcester Bosch fault codes, our guide to Worcester Bosch boiler fault codes explains what each code means before you arrange a repair.

Need help with a Worcester Bosch E5 218 error?

If your boiler keeps displaying the Worcester E5 218 error code, it's best to have it inspected rather than continuing to reset it.

Our boiler repair in London service can diagnose the fault, replace defective components and safely return your heating and hot water to normal.

Get lightning fast quotes. Alternatively, we do offer site surveys where needed.