BoilerFaultCodesYour boiler's internal temperature control sensor is failing or reporting incorrect information, preventing the system from heating up properly.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Thermostat out of calibration or faulty.
What causes this fault?
This fault occurs when the boiler's internal sensors can no longer accurately measure the temperature of the water inside the unit. The most common reason is that the mechanical thermostat or sensor has degraded over time, causing it to send incorrect signals or fail completely 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 D(1) — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Potterton Flamingo RS40 RS50 is discontinued — time for a new one?
Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.
Affiliate links — we may earn a commission at no extra cost to you.