Your boiler's internal control board has become too hot and has shut down the system to prevent any electrical damage.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Electronic temperature too high
What causes this fault?
This fault occurs when the boiler’s central brain, the PCB, reaches an unsafe operating temperature. It is usually caused by heat radiating from a failing internal component or poor ventilation around the control box itself. To prevent the delicate electronics from melting or catching fire, the system instantly shuts down as a safety precaution.
This fault is more common during the peak of winter when the boiler is running at maximum capacity for long periods, leading to higher internal temperatures within the casing.
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.65 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Vaillant ecoMAX Pro 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.