High
E2 on Worcester Bosch 537i

Your boiler has lost the ability to accurately measure the water temperature, so it has shut down to prevent overheating.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

What the manual says

Manufacturer manual

CH flow NTC sensor defective (short circuit/interruption).

From this model's manual
Verified against the Worcester Bosch 537i installation & service manual, page 46.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

What causes this fault?

This fault occurs when the internal sensor responsible for tracking the temperature of water leaving the boiler fails to send a reliable signal to the main control board. The most common reason is that the sensor's internal components have worn out over time or a loose electrical connection has developed within the wiring harness. Because the boiler no longer knows how hot the water is, it shuts down as a safety precaution to prevent overheating.

This fault often appears at the start of autumn when the heating system is first turned on after being idle all summer, which can stress aging electronic components.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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