BoilerFaultCodesYour boiler has stopped working because its internal temperature sensor is not positioned or connected correctly, preventing it from heating your home safely.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Mounting fault sensor S1
What causes this fault?
This fault occurs when the boiler's main internal temperature sensor is not properly attached to the pipework or has disconnected from the control board. The system shuts down as a safety precaution because it can no longer accurately monitor the water temperature leaving the heat exchanger. The most common reasons are a loose mounting clip, a vibrating sensor, or a fault in the wiring harness connecting the components.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like f015 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Could it be time for a new boiler?
If repair costs are adding up, a new energy-efficient boiler could be the smarter long-term choice.
Affiliate links — we may earn a commission at no extra cost to you.