High
125 on Main Insul 7

Your boiler is failing to detect the expected temperature rise after the flame ignites, which means it cannot safely heat your water or radiators.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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

If between 15 and 30 seconds of the burner lighting, the primary water temperature has not changed by 1° C, or if within 10 minutes of the burner lighting, the primary water

From this model's manual
Verified against the Main Insul 7 System 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.

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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