Boiler
F16
The F16 error code on a Ferroli boiler indicates a flow temperature sensor fault — specifically that the boiler is detecting an abnormally high or erratic temperature reading from its central heating flow sensor. It’s a moderately serious fault that will lock out your boiler until resolved.
What does this error mean?
Your Ferroli boiler continuously monitors the temperature of water leaving the heat exchanger via a flow (or ‘NTC’) sensor. When the boiler detects that the flow temperature has exceeded safe limits — or that the sensor is sending a faulty signal — it triggers F16 and shuts down as a safety precaution. This prevents overheating and potential damage to internal components.
Est. repair cost
£80–£180 for sensor replacement; £150–£350+ for pump or PCB fault (parts and labour, Gas Safe engineer)
🔍 Likely causes
🛠️ Step-by-step fix
Step 1 — Reset the boiler: Press and hold the reset button (usually marked with a flame symbol) for 3–5 seconds. If F16 clears and the boiler fires up normally, monitor it for 30 minutes to see if the fault returns.
Step 2 — Check your system pressure: Look at the pressure gauge on the boiler fascia. It should read between 1–1.5 bar when cold. If it’s below 1 bar, top it up via the filling loop (refer to your Ferroli manual for the correct procedure for your model).
Step 3 — Check that all radiator valves are open: Closed lockshield or thermostatic valves reduce water flow and can cause overheating. Ensure valves on all radiators are fully open to improve circulation.
Step 4 — Bleed your radiators: Air trapped in the system restricts water flow and can contribute to overheating. Use a radiator key to bleed each radiator until only water (no air) escapes, then re-check system pressure.
Step 5 — Do not attempt further DIY: Replacing the NTC sensor, inspecting the pump, flushing the heat exchanger, or checking PCB wiring involves working on a gas appliance and must only be carried out by a Gas Safe registered engineer. Stop here and call a professional.
📞 When to call a professional
If the F16 fault returns after a reset and the basic checks above haven’t resolved it, you must call a Gas Safe registered engineer — do not attempt to open the boiler casing or touch any internal components. Tell the engineer: ‘My Ferroli boiler is showing F16, which I understand is a flow temperature sensor fault, and it’s locking out after reset.’ This gives them exactly what they need to diagnose efficiently.
⚖️ Repair or replace?
An NTC sensor replacement typically costs £80–£180 including parts and labour — a straightforward job for an engineer. If the fault lies with the PCB or pump, expect £150–£350+. For boilers over 10–12 years old, weigh repair costs against a new Ferroli or alternative A-rated combi, which starts around £1,800–£2,500 fully installed; if repairs exceed 50% of replacement cost, replacing is usually the smarter investment.