Ferroli F50 Fault Code: Causes, Fixes & Repair Costs
What does the Ferroli F50 fault code mean?
The F50 code appears on Ferroli boilers when the control board (PCB) detects a problem with the gas valve modulation coil circuit. Specifically, the PCB monitors the current flowing through the modulation coil, and if that current drops below the minimum threshold — or the circuit appears open (broken) — it immediately raises the F50 fault. Unlike Ferroli's 'A' prefix lockout codes, which always require a manual reset button press, F50 is a blocking fault: the boiler suspends operation but may recover automatically if the underlying condition clears on its own. In practice, though, most F50 faults require an engineer visit to properly diagnose whether the root cause is in the modulation coil itself, the wiring between coil and PCB, or the PCB's internal circuitry.
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
- Gas valve modulation coil failure Common
The modulation coil inside the gas valve controls how much gas is allowed through at any given moment. Over time the coil windings can develop an inter-turn short circuit or break completely (open circuit), either of which causes the PCB to see an out-of-range current reading and raise F50. This is the most hardware-specific cause and requires an engineer to test the coil resistance with a multimeter and, if faulty, replace the gas valve assembly.
- Wiring fault between coil and PCB Common
The low-voltage wiring loom that connects the modulation coil to the PCB can suffer from loose connector pins, corrosion on terminals, or a break caused by vibration or heat cycling. A broken wire in this circuit will look identical to an open-circuit coil from the PCB's perspective. An engineer can trace the wiring back from the gas valve connector, and a minor re-wire or connector replacement is a far cheaper fix than a full valve or board change.
- Electrical surge or transient fault on the PCB Sometimes
A brief mains voltage spike — from a power cut, a neighbour's heavy load switching, or a nearby lightning strike — can temporarily confuse the PCB's internal logic and trigger F50 without any physical component having actually failed. In these cases a full power-cycle (removing power at the fused spur for at least 60 seconds) often clears the fault entirely. If the code does not return after the power-cycle, no further action may be needed.
- PCB internal fault or failure Sometimes
The PCB contains the circuitry that drives the modulation coil and measures its current. If a component on the board itself fails — such as a driver transistor or a sensing resistor — the board may misread the coil circuit and flag F50 even when the coil and wiring are fine. This is confirmed when an engineer tests the coil and wiring, finds both healthy, but the fault persists. PCB replacement is the resolution in this scenario.
How to fix it
- Check for a wider power or gas supply issue DIY safe
Before anything else, confirm your gas supply is working (check other gas appliances in the house such as a hob or gas fire). Also check your consumer unit for any tripped breakers on the boiler circuit. There is no point resetting the boiler if it has no gas or power.
- Perform a full power-cycle at the fused spur DIY safe
Switch the boiler off at the fused spur (the dedicated switch near the boiler, not just the boiler's own controls) and leave it completely de-energised for at least 60 seconds. Then restore power. This is different from pressing the boiler's reset button and can clear transient PCB faults caused by electrical surges. If F50 disappears and does not return within an hour of normal use, the fault was likely a one-off electrical event.
- Reset the boiler using its reset button (up to twice more) DIY safe
If F50 reappears after the power-cycle, press and hold the boiler's reset button as described in your user manual (typically 3–5 seconds). You can attempt this up to two or three times in total. Do not keep resetting repeatedly — if the fault returns each time, something physical needs attention and further resets will not help.
- Note whether the fault clears temporarily or returns immediately DIY safe
Keep a brief note of what the boiler does after each reset attempt: does it fire up and run for a while before F50 returns, or does it refuse to fire at all? This information is genuinely useful to the engineer — if the boiler fires briefly it suggests an intermittent coil or wiring fault, whereas an immediate return of F50 at ignition points more towards a PCB or wiring issue.
- Call a Gas Safe registered engineer to diagnose and repair Gas Safe engineer
If F50 persists after the power-cycle and reset attempts, a Gas Safe registered engineer is required. The engineer will use a multimeter to ring (test the resistance of) the gas valve modulation coil, checking for an open circuit or inter-turn short. They will also inspect the wiring loom and connector terminals between the coil and PCB. If the coil and wiring test good, the PCB itself will be tested using a voltmeter. Depending on findings, the fix will be a wiring repair, a gas valve replacement, or a PCB replacement — do not attempt any of these yourself.
Parts you may need
- Gas valve assembly (including modulation coil) · from £130
- PCB / control board · from £160
- Wiring loom / connector repair kit · from £25
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 £200–£350, depending on the underlying cause.
Frequently asked questions
Is the Ferroli F50 a lockout or a blocking fault?
F50 is a blocking fault, not a lockout. Ferroli uses an 'A' prefix (e.g. A01) for lockout faults that always need a manual reset button press to restart the boiler. 'F' prefix codes like F50 are blocking faults, meaning the boiler suspends operation but can theoretically recover by itself if the condition clears. In practice F50 rarely clears without intervention, but it does mean a simple power-cycle or reset is a reasonable first step before calling an engineer.
Can I fix an F50 fault myself, or do I need an engineer?
The only homeowner actions worth trying are a power-cycle at the fused spur and one or two reset button presses — these take a few minutes and cost nothing. Everything beyond that involves either the gas valve or the PCB, both of which must only be worked on by a Gas Safe registered engineer. Attempting DIY gas valve work is illegal and dangerous.
How much does it cost to fix a Ferroli F50 in the UK?
Most F50 faults are resolved by one of two repairs: gas valve replacement (typically £250–£350 including parts and labour) or PCB replacement (typically £200–£300 including parts and labour). A simple wiring repair costs less and is often at the lower end of a standard call-out charge. Bear in mind that on older Ferroli models (particularly those over 10 years old), PCB parts can be expensive and sometimes difficult to source, which can push costs higher — in those cases it is worth getting a new boiler quote alongside the repair quote.
My Ferroli boiler is showing F50 and F51 — are they the same fault?
F50 and F51 are closely related codes on Ferroli boilers. F50 specifically points to the gas valve modulation coil circuit (open circuit or below-threshold current), while F51 is also associated with a PCB or control board internal fault. Because the PCB is the component that detects and flags the coil fault, the two codes can appear for overlapping reasons — particularly when an electrical surge affects the board's logic. The diagnostic and repair approach is the same for both: power-cycle first, then call a Gas Safe engineer to test the coil, wiring, and PCB.