BoilerFaultCodesYour boiler's temperature sensor is stuck on a single reading, meaning the system cannot safely tell if the water is heating up correctly.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Flow sensor constant value fault
What causes this fault?
This fault occurs when the boiler's control chip detects that the temperature sensor is stuck on a single reading even though the burner is firing. The most common reason is that the sensor has developed an internal electrical failure or have become coated in debris, preventing it from registering price temperature changes. In some cases, it can also be caused by a loose connection or damaged wiring between the sensor and the main circuit board.
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.71 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Vaillant ecoMAX 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.