Boiler
F19
The F19 error code on a Ferroli boiler indicates a fault with the flue gas temperature sensor or an overheating condition detected at the flue — it’s a safety lockout that needs attention promptly to prevent further damage.
What does this error mean?
Ferroli boilers display F19 when the flue gas thermostat or sensor detects that exhaust gases are running hotter than they should be, or when the sensor itself has failed and is sending incorrect readings to the PCB. The boiler locks out as a precaution to prevent damage to the flue system or risk of carbon monoxide issues. This is a safety-critical fault — the boiler will not fire until the root cause is resolved.
Est. repair cost
£150–£300 for sensor/flue repair; £350–£500 if PCB replacement is needed. New boiler from £1,800–£2,500 installed.
🔍 Likely causes
🛠️ Step-by-step fix
Step 1 – Reset the boiler: Press and hold the reset button (usually marked with a flame or ‘R’ symbol) for 3–5 seconds. Many temporary sensor spikes will clear on their own. If the boiler fires and runs normally, monitor it over the next hour.
Step 2 – Check the flue outlet outside: Go outside and visually inspect the flue terminal on the exterior wall or roof. Make sure it is not blocked by a bird nest, leaves, ice, or debris. Do not dismantle anything — this is a visual check only.
Step 3 – Check for adequate ventilation: If your boiler is in a cupboard or enclosed space, ensure vents or air bricks are not covered or blocked, as poor air supply can cause combustion problems that raise flue temperatures.
Step 4 – Do not attempt to replace the sensor or inspect internal components yourself: The F19 fault involves the flue and combustion system — any further diagnosis or repair must be carried out by a Gas Safe registered engineer. This is a legal requirement in the UK.
Step 5 – Call a Gas Safe engineer: If the boiler locks out again after resetting, or does not reset at all, stop attempting restarts and book a qualified engineer to diagnose the fault properly.
📞 When to call a professional
If the F19 error returns after a single reset attempt, you must call a Gas Safe registered engineer — do not keep resetting the boiler repeatedly, as this can mask a serious combustion or flue issue. Tell the engineer: ‘My Ferroli boiler is showing an F19 fault code, which I understand relates to the flue gas temperature sensor or flue overheating.’ This will save diagnostic time. If you smell gas at any point, do not reset the boiler — call the National Gas Emergency line on 0800 111 999 immediately.
⚖️ Repair or replace?
A flue gas sensor replacement typically costs £150–£300 including parts and labour from a Gas Safe engineer; a PCB replacement can reach £350–£500. If your Ferroli boiler is over 10–12 years old and this isn’t the first fault, replacement with a modern A-rated combi is worth considering — new boilers start from around £1,800–£2,500 fully installed and come with a manufacturer warranty. For a boiler under 8 years old in otherwise good condition, repair is almost always the better value option.