Saunier Duval F.62 Fault Code: Causes, Fixes & Repair Costs
What does the Saunier Duval F.62 fault code mean?
The F.62 code appears when your Saunier Duval boiler detects that the gas valve has not closed correctly. Rather than continuing to operate in an unpredictable state, the boiler triggers a safety lockout and shuts down completely — stopping both heating and hot water. Because this fault relates directly to gas flow control, it is treated as a serious safety issue and should not be left unattended. The display will flash and alternate between the fault digits to draw your attention. A single reset attempt is reasonable, but if F.62 returns immediately or persistently, a Gas Safe registered engineer must investigate before you use the boiler again.
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
- Faulty or deteriorating gas valve Common
The gas valve is the component directly implicated by F.62. Over years of use, internal seals and mechanical parts wear down, and combustion deposits can build up inside the valve body. This can prevent the valve from achieving a proper gas-tight close, causing the boiler's safety system to intervene and lock out. This is the most frequently identified cause on boilers more than five or six years old.
- Dirty or failed ionisation electrode Common
The ionisation electrode sits in the burner and monitors whether a stable flame is present. If it becomes coated in combustion residue, or if it has degraded electrically, it may report that no flame exists even when gas is flowing. The boiler's control board can interpret this misleading signal as a gas valve closure problem and raise F.62. Regular annual servicing, which includes cleaning the electrode, is the best prevention.
- Low gas supply pressure or air in the pipework Sometimes
The burner needs gas arriving at a steady pressure — typically around 18–21 mbar — to establish a clean, consistent flame. If mains gas pressure is low during a period of high demand, or if air has entered the pipes following supply works or an interruption, ignition will be unstable. The safety controls may then log this as a gas valve fault and display F.62. Other gas appliances in the home failing simultaneously would suggest a supply-side problem.
- PCB fault sending incorrect signals to the gas valve Sometimes
The printed circuit board governs the opening and closing commands sent to the gas valve. If the PCB develops a fault — whether through component failure, moisture ingress, or a wiring connection issue — it may send the wrong signal at the wrong time. This can cause F.62 to appear even when the gas valve itself is mechanically sound. PCB faults tend to be harder to diagnose and are usually confirmed only after other components have been ruled out.
How to fix it
- Check that other gas appliances in your home are working DIY safe
Turn on a gas hob or check a gas fire if you have one. If these appliances are also not working, the problem is likely with the mains gas supply rather than the boiler itself. Contact your gas supplier to check for an interruption or pressure issue in your area before doing anything else.
- Attempt a single boiler reset DIY safe
Locate the reset button on your Saunier Duval boiler — on most models it is marked with a flame symbol or labelled 'Reset'. Press and hold it for a few seconds as described in your user guide. If the boiler fires up and runs normally, monitor it closely over the next hour or so. If F.62 returns, do not keep resetting — repeated resets without a fix can mask a genuine gas safety issue.
- Do not attempt any further DIY investigation — call a Gas Safe engineer Gas Safe engineer
All further diagnosis and repair involves gas components, including the gas valve, burner, ionisation electrode, and PCB. It is a legal requirement in the UK that any work on gas fittings is carried out by a Gas Safe registered engineer. Do not remove the boiler casing or interfere with the gas valve under any circumstances.
- Engineer to inspect and clean or replace the ionisation electrode Gas Safe engineer
The engineer will remove the burner assembly and examine the ionisation electrode for carbon fouling or physical damage. Cleaning the electrode with fine abrasive paper is often sufficient; if it has degraded beyond serviceable condition it will need replacing. This is a relatively low-cost intervention and is often the fix on boilers that are otherwise in good condition.
- Engineer to measure gas inlet pressure at the valve Gas Safe engineer
Using a calibrated manometer, the engineer will confirm that gas is arriving at the burner at the correct pressure — approximately 18–21 mbar for natural gas. Pressure outside this range points to a supply issue or a problem with the gas valve itself regulating flow correctly.
- Engineer to test and replace the gas valve if required Gas Safe engineer
If pressure is within range but the valve is not closing fully or operating as expected, the engineer will replace it with a compatible unit. On Saunier Duval boilers this typically involves disconnecting the gas line, removing the old valve, fitting the replacement, and conducting leak and function tests before returning the boiler to service.
- Engineer to test the PCB if the valve and electrode checks are inconclusive Gas Safe engineer
Should the gas valve and ionisation electrode both check out correctly, the engineer will turn their attention to the PCB. They will look for signs of damage, check wiring harness connections, and where necessary test output signals with appropriate diagnostic equipment. A faulty PCB will need to be replaced — this is one of the more expensive repairs associated with F.62.
Parts you may need
- Ionisation electrode · from £25
- Gas valve (compatible replacement) · from £95
- PCB (printed circuit board) · from £220
- Burner seal / gasket kit · from £18
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 £120–£350, depending on the underlying cause.
Frequently asked questions
Is F.62 on a Saunier Duval dangerous?
It can be. The fault signals that the gas valve has not closed correctly, which in theory means gas flow may not be properly controlled. The boiler locks itself out as a precaution, which is the right response — but you should treat any gas valve fault seriously. Do not attempt to bypass the lockout or keep resetting the boiler repeatedly. Leave the boiler off and get a Gas Safe engineer to assess it promptly. If you can smell gas at any point, do not reset the boiler, open windows, evacuate, and call the National Gas Emergency Service on 0800 111 999.
Can I fix F.62 myself?
The only things a homeowner can safely do are checking that the gas supply is working at other appliances and attempting a single reset of the boiler. Everything beyond that — inspecting the gas valve, cleaning or replacing the ionisation electrode, checking gas pressure, or examining the PCB — must be carried out by a Gas Safe registered engineer. Working on gas fittings without Gas Safe registration is illegal in the UK and extremely hazardous.
How much does it cost to fix an F.62 fault in the UK?
For most people, the repair falls somewhere between £120 and £350 including labour and parts. If the ionisation electrode simply needs cleaning, the bill will be at the lower end — largely a call-out and labour charge. A gas valve replacement typically adds £80–£100 in parts on top of labour, bringing the total to around £200–£350. A PCB replacement is the costliest scenario and can push the total to £400–£550 or more — if your boiler is already old and a PCB replacement is recommended, it may be worth comparing that cost against a new boiler installation.
Why does F.62 keep coming back after I reset it?
If F.62 returns shortly after a reset, the underlying fault has not gone away. Persistent recurrence usually means the gas valve is failing mechanically, the ionisation electrode is too fouled to give an accurate flame reading, or the PCB is sending unreliable signals. Each reset without a fix puts additional strain on the system and does nothing to address the root cause. A Gas Safe engineer needs to carry out a proper diagnosis — frequent lockouts are the boiler telling you that something is genuinely wrong.
Will my boiler warranty or home cover policy pay for this repair?
It depends on your policy and the age of your boiler. If your Saunier Duval boiler is still within its manufacturer warranty period, contact Saunier Duval or your installer first, as gas valve and PCB faults may be covered. If you have a boiler care plan or home emergency cover through your energy supplier or insurer, check whether gas valve faults are included — many policies do cover internal component failures. Always confirm cover before agreeing to repairs, as qualifying repairs can save you hundreds of pounds.