Suppose your Vaillant ecoTEC Pro, ecoTEC Plus, or ecoFIT Pure boiler is showing F61 on the display (often with a permanent red light and no heating or hot water). In that case, you’ve just hit one of the scariest-sounding but actually quite well-understood faults on a Vaillant.
F61 = “Gas valve control defective”
In plain English: the main printed circuit board (PCB) has tried to open or close the gas valve but isn’t getting the correct electrical feedback signal back. The boiler, therefore, locks out completely for safety.
This fault is common across the UK on boilers from about 2012 onwards, especially in hard-water areas like London, the South East, and the Midlands.
The Real Causes of F61 in Everyday British Homes
In order of how often we actually see them:
- The wiring harness or plug to the gas valve has worked loose or become corroded. The small multi-pin connector on top of the gas valve gets hot/cold cycled for years, and the pins become green or the clip breaks.
- Water damage to the main PCB Tiny condensate leaks from the sump or trap drip onto the low-voltage side of the board, and corrode the gas-valve driver circuit.
- Gas valve stepper motor or solenoid has failed The valve itself sticks or the coils burn out (more common after 10–12 years).
- The main PCB gas valve driver has blown. Usually triggered by a short-circuit from water or a power surge.
- Very occasionally – actual gas valve out of calibration (This is the least common – most engineers replace the valve anyway if they’re in there.)
Important: F61 is NOT low gas pressure (that’s F28/F29) and it’s NOT ignition electrodes (that’s F27/F62).
Safe DIY Checks (There Aren’t Many!)
Because F61 is almost always inside the sealed combustion chamber or involves gas-carrying parts, your legal DIY options are extremely limited:
- Reset the boiler Press and hold the spanner/reset button for 5 seconds. If F61 clears once and never comes back – you got lucky (temporary glitch). If it returns within seconds – stop.
- Check the electricity supply Make sure the switched spur hasn’t tripped and the fuse is OK.
That’s it. Do NOT open the case, do NOT wiggle wires, do NOT try to “tap” the gas valve.
When You MUST Call a Gas Safe Engineer (Which Is 99% of F61 Cases)
Everything else is strictly Gas Safe only:
- Removing the front case and combustion cover
- Testing the gas valve coils and stepper motor
- Checking and replacing the wiring harness
- Drying out or replacing the PCB
- Full gas soundness and combustion test after repair
Always check they’re registered at www.gassaferegister.co.uk
Typical 2025 Fixed Repair Prices for Vaillant F61
- New gas valve wiring harness only: £130–£190
- New gas valve complete (Honeywell or Sit): £320–£460 fitted
- Main PCB replacement (most common worst-case): £420–£620 fitted
- Full gas valve + PCB (when both are suspect): £720–£920
- Fixed-price “F61 repair” (many Vaillant specialists now offer this): £380–£550
How to Prevent F61 Happening Again
- Annual service by a Vaillant Advance or Accredited installer – they check the harness and sump for early leaks
- Fit a condensate neutraliser or pro pump if your boiler is in a loft
- Install a good magnetic filter and inhibitor – sludge accelerates component failure
- Consider a surge-protected plug or whole-house surge protection if you’re in a lightning-prone area
If your boiler is 10+ years old and hits F61, many engineers will advise replacement rather than a £800+ repair bill.
Frequently Asked Questions About Vaillant F61
Will resetting get rid of F61?
Only temporarily if you’re very lucky. It nearly always comes straight back.
Is F61 covered by my Vaillant warranty?
Yes – if the boiler is still within its 5–10 year warranty AND has a full service history by a Vaillant-trained engineer.
My boiler is only 6 years old – why F61 already?
Usually condensate dripping onto the PCB or a loose harness – still warranty if serviced every year.
F61 or F62 – what’s the difference?
F61 = gas valve feedback wiring or driver fault
F62 = gas valve closing fault (similar repair)
Should I repair or replace?
Under 10 years and good service history → repair (usually £400–£550).
Over 12 years → new boiler often makes more sense.
Stay warm,
The Boilers2Go Team
With years of experience in boilers and home improvements in general, Myles Robinson is a passionate advocate for making home heating simpler, safer, and more affordable for households across the UK. With years of experience in the heating industry, Myles combines hands-on knowledge with a focus on customer-first service, helping homeowners choose the right boiler, understand their systems, and keep their heating running efficiently all year round. His articles break down complex topics into clear, practical advice you can trust.