Overview
The F.62 fault on Vaillant EcoTEC Pro / EcoTEC Plus boilers indicates a problem with the gas valve — specifically a shut‑off delay or failure related to the valve. In practice the boiler has detected that the gas valve is not behaving as expected (not opening when it should, not closing properly, or leaking), and the controller has put the appliance into lockout to protect against unsafe gas flow. The same symptom can also be caused by related electronic faults such as a faulty PCB or intermittent wiring between the PCB and the valve. This is a high‑severity fault because it involves the gas supply and the combustion safety chain. If the valve leaks when the boiler should be off, that creates a risk of gas entering the home. If the valve fails to open, the boiler will not ignite and you will lose heating and hot water. Because of the risks and the legal requirements for work on gas appliances, F.62 is not a DIY repair: you can perform a few safe checks and a reset, but diagnosis and any replacement or gas‑side repairs must be done by a Gas Safe registered engineer. If you smell gas, or suspect a leak, treat it as an emergency: evacuate the property, avoid operating electrical switches or appliances, shut off the gas at the meter if it is safe to do so, and call the national gas emergency number immediately.
Possible Cause: Error with gas valve – switch off delay
Troubleshooting Steps
Safety first:
1. If you smell gas or see/ suspect a leak: get everyone out of the building, do not operate switches or sockets, do not use phones inside the building, turn off the gas supply at the meter only if it is safe to do so, and call the gas emergency service immediately (in the UK call 0800 111 999). Do not attempt repairs.
2. If there is no smell of gas, proceed with caution. Before touching the boiler, switch off the electrical supply at the isolator or fuse box if you need to remove covers. Do not probe live parts unless you are qualified.
Initial homeowner checks you can safely do:
1. Look and listen: note the exact fault code (F.62) and whether other codes appear at the same time (e.g. F.61, F.28, F.29). Take a photo of the display and note when the fault first appeared and any recent events (power cuts, storms, service history).
2. Check other gas appliances: confirm your gas supply to the house is working by testing another gas appliance (hob, gas fire) without turning anything on/off at the boiler. If other appliances do not work, contact your gas supplier.
3. Check the boiler’s external flue and termination for obvious blockages (bird nest, debris). A blocked flue can prevent ignition sequences but does not directly cause F.62; still clear obstructions safely if visible.
4. Check the boiler’s gas isolation valve (external shut‑off lever/valve to the boiler) is in the open position. Do not force valves; just confirm position.
5. Try a basic reset: follow the boiler’s reset procedure (usually a reset button marked with a flame symbol or described in the manual). If the fault clears and the boiler fires, monitor it — a temporary reset is not a repair and the fault will often return. Record whether the boiler runs normally after reset and for how long.
Specific diagnostic observations to note for the engineer (do not attempt to disassemble or replace parts yourself):
1. Does the boiler try to fire when demand is made (heating or hot water) and then display F.62, or does it lockout immediately?
2. Is there any intermittent behaviour — sometimes runs, sometimes faults? Intermittent faults often point to wiring/PCB issues.
3. Any signs of water ingress or corrosion inside the boiler, recent leaks, or evidence of electrical damage? Water can damage the PCB and cause control faults.
4. Any previous repairs, PCB replacements, or component swaps recently performed?
What a qualified engineer will do (why you need to call a professional):
1. Carry out a safe isolation and full electrical and gas pressure check, then verify the valve operation and communication between the PCB and the gas valve coils.
2. Test for gas valve leakage/closing and measure gas pressure during an ignition attempt. They will use specialist tools to confirm whether the valve is stuck, leaking or not being driven correctly.
3. Inspect and test the PCB and the wiring harness for intermittent faults, shorts or earth leakage. They may replace the PCB if it is faulty, or re‑terminate wiring/connectors.
4. Replace the gas valve assembly if it is mechanically faulty or leaking. After any gas‑side work they will carry out a gas tightness test and full commissioning to current regulations.
5. Check the rest of the boiler (sensors, fan, ignition, condensate) to rule out contributory issues.
Practical next steps for you now:
1. If you smell gas: follow the emergency actions above and call the gas emergency number.
2. If you do not smell gas: try a reset once and see whether the boiler will run. If it returns to F.62 or will not run, turn the boiler off and isolate gas if you are concerned. Do not continue to use a boiler showing F.62 as a persistent fault.
3. Contact a Gas Safe registered engineer and provide them with: boiler model, serial number, the fault code(s), photos of the display, and details of any intermittent behaviour or recent events. Mention if the boiler ran after a reset and for how long.
4. Arrange for the engineer to inspect and repair. Only a Gas Safe engineer should replace the gas valve or PCB, test for gas tightness, and recommission the boiler.
Preventive note: arrange annual servicing by a Gas Safe engineer to catch wear in valves, check wiring and the PCB, and reduce the risk of this fault recurring. Maintain a record of services and repairs to help future diagnosis.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Vaillant EcoTEC Pro / EcoTEC Plus.