Boiler
F13
The F13 error code on a Ferroli boiler indicates a fault with the flow (central heating) temperature sensor — it’s a relatively common fault that will lock out your boiler until resolved, leaving you without heating or hot water.
What does this error mean?
The F13 code tells you that the boiler’s control board is receiving an abnormal signal from the NTC flow temperature sensor — the probe that monitors how hot the water is as it leaves the boiler. The reading is either out of range, missing entirely, or inconsistent, so the boiler shuts down as a safety measure. This is not a dangerous fault in itself, but the boiler will not fire until the sensor issue is resolved.
Est. repair cost
£80–£180 for NTC sensor replacement by a Gas Safe engineer (parts + labour)
🔍 Likely causes
🛠️ Step-by-step fix
Check the boiler pressure gauge — if it reads below 1 bar, repressurise the system to 1–1.5 bar using the filling loop and attempt a reset.
Press and hold the reset button (usually marked with a flame or ‘R’ symbol) for 3–5 seconds. If F13 clears and the boiler fires normally, monitor it over the next 24 hours.
If F13 returns after reset, check your boiler manual to confirm F13 is specifically listed as a flow sensor fault on your model (Ferroli Modena, Optimax, etc.), as codes can vary slightly by range.
Do not attempt to access internal components, disconnect wiring, or replace the sensor yourself — this requires a Gas Safe registered engineer, as the work involves dismantling gas appliance parts.
Turn the boiler off at the power switch and call a Gas Safe engineer. Tell them the boiler displays F13, the model name and age, and whether the fault appeared suddenly or has been intermittent.
📞 When to call a professional
Call a Gas Safe registered engineer immediately if the F13 code does not clear after a single reset, or if it keeps returning. Tell the engineer: ‘My Ferroli boiler is showing an F13 fault code, which I understand relates to the flow NTC temperature sensor — it may need testing or replacing.’ Do not attempt to bypass the lockout or tamper with internal components.
⚖️ Repair or replace?
An NTC flow sensor replacement by a Gas Safe engineer typically costs £80–£180 all-in, including parts and labour. If your Ferroli boiler is over 10–12 years old and this fault is accompanied by other recurring issues, it’s worth getting a replacement quote — a new boiler from a reputable brand will cost £1,800–£3,000 installed but will be more efficient and carry a fresh warranty. For a boiler under 10 years old in otherwise good condition, repair is almost always the right call.