BoilerFaultCodesYour boiler has lost its connection with the internal sensor that monitors the temperature of the water returning to the unit.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: E-combi oneE-System oneClas Net one CombiClas one Combi
What causes this fault?
This fault occurs when the boiler's control board can no longer read the temperature of the water coming back from your radiators. The most common reason is that the return sensor has failed internally or the electrical wiring connecting it to the main computer has become loose or damaged. Without this data, the boiler shuts down as a safety precaution because it cannot accurately monitor the heat levels within the system.
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 205 — 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.