BoilerFaultCodesYour boiler has detected a fault with one of its temperature sensors, which means it cannot accurately monitor the water temperature and has shut down as a safety precaution.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: S2 sensor defect. Replace S2.
What causes this fault?
This fault occurs when the boiler's control board loses communication with the secondary temperature sensor, which monitors the water returning to the unit. The most common cause is the sensor's internal electrical resistance failing due to age, or moisture causing a poor connection in the wiring harness.
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 4 — 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.