BoilerFaultCodesYour boiler has lost its ability to monitor the temperature of your hot water cylinder because a sensor has developed an electrical fault.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Cylinder temperature sensor short circuit
What causes this fault?
This fault occurs when the electrical monitoring system detects a short circuit in the sensor that measures the heat of your hot water tank. The most common reason is that the internal components of the sensor have failed, or the wiring connecting it to the boiler has become damaged or pinched. As a result, the boiler can no longer safely determine if the water is at the correct temperature and will stop heating the cylinder as a safety precaution.
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 F.91 — 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.