BoilerFaultCodesYour boiler has lost connection with a temperature sensor that monitors the main water flow, likely due to a broken wire or a faulty sensor.
This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.
Technical description: Lead break: System flow temperature sensor (low loss header)
What causes this fault?
This fault occurs when the boiler's control board can no longer detect a signal from the temperature sensor located on your system's piping. The most common reason is that the internal wiring has become damaged or the sensor itself has worn out and failed. Without this data, the boiler cannot accurately measure the water temperature leaving the unit, causing it to stop operating for safety reasons.
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 28 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.