High
Overheat Limit Thermostat on Potterton Prima 30B

Your boiler has shut itself down completely because the internal water temperature has become too hot.

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

Red L.E.D. will start to flash. Press the reset button (Do Not use excessive pressure), the Red L.E.D. will stop flashing and the boiler will attempt to re-light. If the control does not reset, leave the boiler for approx. 15 minutes before pressing the reset button again.

From this model's manual
Verified against the Potterton Prima 30b installation & service manual.
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 water inside the boiler reaches a dangerous temperature, triggering a mechanical safety switch to cut off the gas for your protection. The most common reasons are a failed pump failing to move hot water away from the heat exchanger, or a buildup of limescale and sludge creating 'hot spots' within the unit.

This issue often surfaces during the first cold snap of autumn when a heating pump that has been sitting idle all summer fails to start up correctly.

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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Avoid the next call-out bill

A cover plan would handle faults like Overheat Limit Thermostat: no call-out fees, no surprise bills.

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