F61 is a gas-valve control fault across the Vaillant Group brands (Vaillant, Glow-worm, Saunier Duval, Heatline, Protherm): the control board could not correctly drive or read back the gas valve. Ferroli uses it for an internal board error. Anything involving the gas valve is strictly Gas Safe work — do not keep resetting it.
The brand is printed on the front casing. Tap your brand for the full causes, fixes and repair costs.
F61 brand by brand
The F61 code (sometimes displayed as A61 on certain Ferroli models) points to an internal error on the boiler's AGC01 printed circuit board — the main control unit that manages all key functions including gas valve operation. When this fault appears, the boiler locks out completely, cutting off both heating and hot water until the root cause is identified and resolved. Because the PCB is responsible for signalling the gas valve to open and close safely, any breakdown in that communication chain triggers this lockout as a protective measure. Note that fault code behaviour can vary slightly between Ferroli model generations, so always quote your exact model number when speaking to an engineer.
Causes, fixes & costs for Ferroli F61 → · All Ferroli codes
The F61 code appears when your Glow-Worm boiler detects a problem with the gas valve control system. In practice this sits at the crossroads of two related faults: the boiler's PCB (printed circuit board) is responsible for sending precise electrical signals to open and close the gas valve, so a failure in either the PCB's output circuitry or in the gas valve itself can trigger this code. Glow-Worm's own classification groups F61 through F68 as main board faults, with F61 specifically flagging the gas valve control pathway. The boiler will lock out and refuse to fire until the root cause is identified and resolved. Because both gas components and the control board are involved, this fault always requires attention from a Gas Safe registered engineer — it is not safe or appropriate for a homeowner to attempt repairs beyond a single reset.
Causes, fixes & costs for Glow-worm F61 → · All Glow-worm codes
The F61 code appears when your Heatline boiler's control board detects a problem in the gas valve circuit. The PCB sends precise electrical signals to open and close the gas valve — if those signals aren't being sent correctly, received by the valve, or acted upon, the boiler locks out as a safety precaution. Heatline boilers share the same fault code system as Vaillant (both are part of the Vaillant Group), so this code carries exactly the same meaning across both brands. With F61 active, the boiler will not fire, meaning no central heating or hot water until the underlying fault is resolved.
Causes, fixes & costs for Heatline F61 → · All Heatline codes
The F.61 code appears on Protherm boilers when the control board (PCB) cannot correctly communicate with or actuate the gas valve. In plain terms, the boiler's brain is sending a signal to open the gas valve but isn't getting the expected response back — or isn't able to send the signal at all. Because the gas valve is central to safe combustion, the boiler shuts itself down immediately as a precaution. You'll typically see F.61 alongside a red or amber warning light, and the boiler will not ignite until the underlying issue is resolved. This fault is shared across the wider Vaillant Group platform, so it behaves identically on Vaillant, Glow-worm, and Protherm boilers that use the same control architecture.
Causes, fixes & costs for Protherm F.61 → · All Protherm codes
The F.61 fault code signals that the boiler's PCB (printed circuit board) has detected a problem controlling or communicating with the gas valve. The gas valve is responsible for regulating gas flow to the burner, and if the PCB cannot send a reliable command to the valve — or cannot confirm the valve is responding correctly — the boiler shuts down as a safety precaution. This is a lockout fault, meaning the boiler will not attempt to fire again until the underlying issue is resolved and the unit is manually reset. Saunier Duval is part of the Vaillant Group, so the F.61 code also appears on some Vaillant ecoTEC and Glow-worm models with broadly the same meaning. On most displays, the fault code flashes and two characters alternate — the second number typically has a decimal point after it to distinguish it from other codes.
Causes, fixes & costs for Saunier Duval F.61 → · All Saunier Duval codes
The F.61 code on a Vaillant boiler signals a gas valve control or communication fault. In plain terms, the boiler's control board (PCB) is trying to operate the gas valve but isn't getting the correct response back, so the boiler deliberately locks out to keep you safe. The most likely culprits are a faulty or seized gas valve, a damaged wiring harness between the valve and PCB, or a fault on the PCB itself. Because it involves the gas valve, F.61 is a safety-critical fault that must be diagnosed and repaired by a Gas Safe registered engineer.
Causes, fixes & costs for Vaillant F.61 → · All Vaillant codes
Frequently asked questions
Is the F61 fault code the same on every boiler?
Broadly, yes — on Ferroli, Glow-worm, Heatline, Protherm, Saunier Duval and Vaillant the F61 code points to the same class of fault, and the recommended response is similar. Model-specific details such as sub-codes and reset procedures still vary, so follow the page for your own brand.
Can I fix a F61 fault myself?
Not usually. On every brand listed, F61 points to a fault that needs a suitably registered engineer to diagnose and repair. A single reset to rule out a transient glitch is reasonable; repeated resets are not.
Who should I call about a F61 fault?
For gas boilers, a Gas Safe registered engineer — it is a legal requirement for any work on the appliance. If you smell gas at any point, leave the property and call the National Gas Emergency line on 0800 111 999.
General guidance only — not a substitute for professional advice, and not certified by a registered engineer.
Any work on a gas appliance must be carried out by a Gas Safe registered engineer. If you smell gas, call 0800 111 999.
