Overview
F.62 on a Vaillant Turbomax Plus 824/828E means the boiler has detected a fault in the gas valve/ignition circuit — typically the boiler tried to ignite but the gas valve failed to operate as expected (failed to open, failed to close, or did not respond to the PCB). The boiler will lock out as a safety measure to prevent uncontrolled gas flow or a failed ignition. Common underlying causes are a stuck or mechanically failed gas valve, a faulty PCB or intermittent electrical connection between the PCB and the gas valve, incorrect gas pressure or a faulty gas pressure sensor. It can also show after the boiler overheats and the system goes into a protective shutdown. This is a high-severity fault because it involves the gas supply and the risk of a gas leak or unsafe operation. It is not a DIY repair. Homeowner checks can safely identify obvious external symptoms (smell of gas, visible damage, or if the fault clears after a cool-down and reset) but any internal inspection, testing, adjustment or replacement of the gas valve, PCB or gas-pressure components must be carried out by a Gas Safe registered engineer. If you smell gas, evacuate and call the emergency gas number immediately before doing anything else.
Possible Cause: Defective gas valve closure mechanism
Troubleshooting Steps
Safety precautions:
1) If you smell gas: stop using electrical switches, ventilate the property by opening doors and windows, do not smoke or use naked flames, leave the building and call the gas emergency number (in the UK 0800 111 999) and Gas Safe for repairs. Do not attempt to restart the boiler.
2) If there is no smell of gas, isolate the boiler gas supply at the boiler gas cock, turn the boiler off at the mains, and keep it off until a qualified engineer has checked it.
3) Do not attempt to dismantle, adjust or replace the gas valve, PCB or gas pipe connections yourself. These are gas‑safe tasks.
Initial checks a homeowner can safely do:
1) Note the exact error code and take a clear photo of the display and any additional codes. This helps the engineer.
2) Allow the boiler to cool if it has overheated. The existing note that the boiler exceeded maximum temperature means the thermal cutout may have tripped — allow 20–30 minutes to cool.
3) Try a single reset following the boiler manual (usually by switching the boiler off and on or using the reset button). Do not repeatedly reset the boiler if the fault returns immediately; repeated resets can mask the problem and are unsafe.
4) Check that the home’s gas supply is working by briefly testing another gas appliance (hob or gas fire) — only if you know this is safe to do. If other appliances are not working, contact your gas network supplier.
5) Visually inspect the boiler front for obvious water ingress, burn marks or corrosion around connectors and PCB area. Do not probe connectors; only note visible damage and photograph it for the engineer.
6) Check the boiler’s system pressure gauge (water pressure) and ensure it is within the normal operating range (usually 1–2 bar) — while F.62 is gas-related, extreme system faults or overheating can be related.
7) Check the flue terminal externally for obvious blockages (birds’ nests, debris) that might impede safe operation. Do this from ground level only — do not climb onto roofs unless you are competent and safe.
Safe diagnostic information to prepare for the Gas Safe engineer:
1) Record when the fault first appeared, what you were doing (calling for heat/hot water), and whether it followed an overheating condition.
2) Provide photos of the error code, internal visible damage (if any), the gas meter reading and whether other gas appliances work.
3) If you performed a reset, record whether the boiler attempted to fire and whether the error returned immediately or after some time.
What a Gas Safe engineer will typically check and do (do not attempt yourself):
1) Verify there is no gas leakage at the boiler using proper gas detectors and tightness tests.
2) Check correct incoming gas pressure at the appliance and test the gas valve operation (electrically and mechanically) and its response to the PCB commands.
3) Inspect and test the PCB, connectors and wiring for intermittent faults, signs of water damage, burning or dry joints. Replace PCB if faulty.
4) Test the gas pressure sensor (where fitted) and associated components; replace if failed.
5) Replace the gas valve where it is mechanically stuck, leaking or electrically defective. After replacement they will commission and test the boiler for correct safe operation.
6) Run a full safety and combustion check and leave the boiler operating only when it is safe and within specification.
When to call a professional: Call a Gas Safe registered engineer immediately if the fault persists after a single safe reset, if you detect any smell of gas, or if you see signs of water-damaged electronics or burning. Do not attempt internal repairs, gas-tightness tests, valve or PCB replacement yourself. Keep the boiler isolated at the gas cock and turned off until the engineer arrives.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Vaillant Turbomax Plus 824/828E.