Ferroli A13 Fault Code: Causes, Fixes & Repair Costs
What does the Ferroli A13 fault code mean?
The A13 code indicates that the flue probe (also called the exchange or flue gas sensor) has either failed or is sending readings that fall outside acceptable limits. As a result, the boiler shuts down completely and will not restart until the fault is cleared and a manual reset is performed. Ferroli uses 'A' prefix codes to denote hard lockouts of this kind — the equivalent non-lockout version of this fault is F13, which may clear automatically if the underlying condition resolves itself, whereas A13 always requires a deliberate reset. In plain terms, the boiler has detected a problem with the sensor that monitors conditions in the flue and has locked out as a precaution.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Failed or damaged flue probe Common
The flue temperature sensor itself has developed a fault — either through corrosion, age-related degradation, or an internal electrical failure. When the sensor's resistance falls outside the expected range, the boiler locks out rather than operate without accurate flue-gas data. This is the most common root cause of an A13 lockout.
- Wiring fault on the probe circuit Common
The wiring connecting the flue probe to the PCB can suffer from loose terminals, corrosion at connectors, or insulation damage — particularly on older or heavily cycled boilers. The PCB cannot distinguish between a bad probe and a bad connection, so either will trigger A13.
- Blocked or obstructed flue terminal Sometimes
A partially blocked flue outlet — caused by debris, a bird nest, or ice build-up in very cold weather — can affect flue conditions in a way that the sensor detects as abnormal. Checking the external terminal from ground level is one of the few safe checks a homeowner can carry out.
- Flue duct corrosion or loose flue joints Sometimes
Over years of use, the flue duct sections can corrode internally or joints can loosen slightly. If flue gases are escaping or diluted before reaching the probe, readings will be erratic. A puffing sound from the boiler can accompany this fault. An engineer needs to inspect and replace the affected sections.
- Fan performance issue Sometimes
If the fan is not moving flue gases at the correct rate, the probe may record temperatures or pressures that cause the boiler to lock out. A weakening or failing fan can therefore trigger A13 indirectly, even if the probe itself is undamaged.
- PCB fault Rare
In rare cases, the PCB incorrectly interprets the signal from an otherwise healthy flue probe. This is usually only suspected once the probe and wiring have both been tested and confirmed serviceable.
How to fix it
- Check the external flue terminal for visible blockages DIY safe
From ground level, look at the flue outlet on the outside wall or roof for any obvious obstruction — debris, ice, or signs of a bird nest blocking the terminal. Do not attempt to climb or access the terminal yourself; simply note what you can see and report it to the engineer.
- In cold weather, check whether the condensate pipe is frozen DIY safe
If temperatures have dropped below freezing, the plastic condensate pipe running to a drain outside may have frozen solid, causing knock-on sensor faults. Carefully pour warm (not boiling) water over the external section of the pipe to thaw it, then attempt a reset.
- Reset the boiler DIY safe
Locate the reset button on the Ferroli control panel — it is typically marked with an 'R' symbol. Press and hold it for one to two seconds. If the boiler fires up and the A13 code does not return within the next hour or so, the fault may have been a transient issue. However, do not reset the boiler more than two or three times in total. If the lockout returns repeatedly, continuing to force resets risks damaging the heat exchanger and fan.
- If the fault persists, do not attempt further DIY — call a Gas Safe registered engineer Gas Safe engineer
Diagnosis and repair of the flue probe, its wiring, the fan, or any flue duct components must be carried out by a Gas Safe registered engineer. The engineer will test the probe's resistance, inspect the wiring loom back to the PCB, check the fan's performance, and examine the flue system for corrosion or loose joints. Always verify an engineer's Gas Safe registration at gassaferegister.co.uk and ask to see their ID card before any work begins.
- Arrange replacement of the faulty component as identified by the engineer Gas Safe engineer
The most likely outcome is replacement of the flue probe sensor itself. If the fan or sections of flue ducting are also found to be at fault, these will need replacing at the same visit where possible. Ask for a written quote before authorising work, particularly on older Ferroli models where parts availability can vary.
Parts you may need
- Ferroli flue probe / exchange temperature sensor · from £35
- Flue probe wiring harness / connector · from £20
- Flue fan assembly (model-specific) · from £95
- Flue duct section / terminal kit · from £45
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £100–£280, depending on the underlying cause.
Frequently asked questions
What is the difference between Ferroli fault codes A13 and F13?
Both codes point to the same flue probe fault, but they behave differently on the boiler. An F13 is a 'blocking' fault — the boiler shuts down but will attempt to restart automatically once the fault condition clears. An A13 is a hard lockout — the boiler stays off until you manually press the reset button. If the problem is serious enough to cause a lockout rather than a temporary block, it usually means the probe has fully failed or the fault has persisted beyond the boiler's tolerance threshold.
Can I fix a Ferroli A13 fault code myself?
The only steps a homeowner can safely take are checking the flue terminal for obvious blockages, thawing a frozen condensate pipe in cold weather, and resetting the boiler up to two or three times. The probe itself, its wiring, the fan, and any flue duct components must be diagnosed and replaced by a Gas Safe registered engineer. Working on these parts without registration is illegal in the UK and could put your household at risk.
How much does it typically cost to fix a Ferroli A13 fault?
For the most common repair — replacing the flue probe including parts and labour — expect to pay roughly £100 to £180. If the engineer's visit also turns up a fan fault, you could be looking at £180 to £280 all-in. In the less common scenario where the PCB is implicated, costs can rise to £200–£300 or more. Always ask for a written quote before work begins. On older Ferroli boilers (10 years or more), it is worth comparing the repair cost against a replacement quote before committing.
Is it safe to keep using my boiler when the A13 code appears?
No. A13 is a lockout code, which means the boiler has already shut itself down and will not fire. You should not attempt to repeatedly reset the boiler and run it through cycles hoping the fault clears — doing so can overheat the heat exchanger and cause expensive secondary damage. If the lockout returns after one or two resets, treat it as a genuine fault and call a Gas Safe engineer promptly, especially if you are heading into cold weather without heating.