Vaillant Fault Codes
Vaillant Boiler Fault Codes: What They Mean And What To Do
Reviewed by our Gas Safe registered engineers · Last updated 21 July 2026
Vaillant’s ecoTEC range is one of the most common boilers we service across North London, and its fault codes are generally clear once you know what you’re looking at — a letter F followed by two digits, shown on the boiler’s small display.
Quick Answer
F.22 and F.75 are usually pressure-related and often fixable by repressurising. F.28 and F.29 relate to ignition and flame loss and are safety lockouts — worth a professional look rather than repeated resetting.
Not sure which code you have? Call 020 7108 6322 with the exact code and we’ll tell you what it means.
Common Codes
Common Vaillant fault codes
| Code | Meaning | First step |
|---|---|---|
| F.00 | Flow temperature sensor interruption | Needs an engineer — sensor or wiring fault |
| F.10 | Flow temperature sensor short circuit | Needs an engineer — sensor or wiring fault |
| F.20 | Safety shutdown — overheating | Don’t keep resetting; book an engineer |
| F.22 | Low water pressure / dry fire | Repressurise via the filling loop to around 1.3 bar |
| F.23 | Water shortage — large flow/return difference | Check pressure; if normal, needs diagnosis |
| F.24 | Water shortage — rapid temperature rise | Often circulation or pump related — call an engineer |
| F.27 | Flame detected when there shouldn’t be | Safety fault — call an engineer, don’t reset repeatedly |
| F.28 | Failed ignition on start-up | One reset can be tried; if it recurs, needs an engineer |
| F.29 | Loss of flame during operation | Don’t repeatedly reset — book an engineer |
| F.32 | Fan fault | Needs an engineer — fan or wiring |
| F.61 | Gas valve control fault | Gas Safe engineer required |
| F.62 | Gas valve shut-off delay fault | Gas Safe engineer required |
| F.63 | Memory (EEPROM) error | Usually a PCB fault — needs diagnosis |
| F.73 | Water pressure sensor signal too low | Check the gauge reading against what the boiler reports |
| F.74 | Water pressure sensor signal too high | Sensor or wiring fault — needs an engineer |
| F.75 | No pressure change detected on pump start | Check pressure first; if normal, needs diagnosis |
| F.83 | Little or no temperature change on burner start | Often low water or circulation — call an engineer |
| F.85 | Flow and return sensors fitted to the same pipe | Installation fault — needs an engineer |
The exact code set can vary slightly between the ecoTEC Plus, ecoTEC Pro and older ecoTEC models, so treat these as a starting guide rather than a definitive list for your exact model. If your display shows something not covered here, note it down exactly (including any decimal points) and call us.
Common causes
- Low pressure — F.22
- Ignition failure — F.28
- Flame loss — F.29
- Sensor or circulation — F.75
- Limescale build-up
What you may notice
- F code on the display
- No heating or hot water
- Boiler locked out
- Code clears, then returns
- Worse in cold weather
Safe checks you can do
- Read the pressure gauge on the front of the boiler
- If below 1 bar, repressurise via the filling loop to around 1.3 bar
- Try the boiler’s own reset button once
- Check your thermostat has power and is calling for heat
- Note the exact code shown, including any decimal point
Do not attempt
- Removing the boiler casing
- Any work on gas valves, electrodes or burners
- PCB or internal electrical work
- Resetting repeatedly after a lockout
Gas work is Gas Safe registered work by law. Anything behind the casing must be carried out by a Gas Safe registered engineer — and DIY attempts can invalidate your warranty.
When to call a Gas Safe engineer
Call us if an F.28 or F.29 returns after a single reset, if F.75 comes back quickly once pressure is normal, or if a code keeps reappearing. Repeated resetting can mask a developing fault rather than fix it.
- Vaillant’s eBUS-connected controls can report a code reflecting a control issue rather than the boiler — worth checking the thermostat connection first.
- The ecoTEC’s plate heat exchanger is prone to limescale in hard-water areas if no scale reducer is fitted.
- On units past 10 years old, a repeated F.28 is sometimes better addressed with a full service than by chasing individual components.
Our Vaillant repair process
Give us the exact code shown.
A Gas Safe engineer identifies the fault.
You get the cost before any repair starts.
We repair, then test the boiler is running safely.
What Repairs Typically Cost
Typical Vaillant repair costs
Typical North London ranges. F.22 pressure issues are often resolved during the callout itself at no extra cost beyond the visit. You’ll always get the price before any repair begins.
FAQs
Vaillant fault codes — your questions answered
Why does my Vaillant boiler show F.28 only in cold weather?
Ignition can be more marginal in very cold conditions if there’s a borderline gas pressure or ignition electrode issue, which colder weather then tips into a full lockout.
Can I reset an F.75 code myself?
You can try a reset once, but if it returns quickly it usually indicates a genuine pressure sensor or pump circulation fault that needs diagnosing rather than repeated resetting.
Does Vaillant’s app show more detail than the boiler’s own display?
If you have a Vaillant sensoCOMFORT or similar smart control linked to the boiler, it can sometimes show a more specific sub-code than the boiler’s own basic display, which is worth checking before calling.
Is it true Vaillant boilers are harder to get parts for than other brands?
Not generally — Vaillant is one of the most common brands in the UK and parts availability is normally good, though very old or discontinued models can occasionally take longer to source specific components.
Why does my boiler display a code briefly then clear itself?
This can happen with a marginal, intermittent fault that resolves itself temporarily, such as a slight pressure fluctuation. It’s worth keeping a note of when it happens in case it becomes more frequent.
Do all Vaillant models use the same F-code numbering?
Broadly yes across the ecoTEC range, though older legacy models before the ecoTEC Plus sometimes used a slightly different set. Check your specific model’s manual if you’re unsure.
Is an F.22 always about the whole system, or could it just be the sensor?
Usually it’s a genuine low pressure reading, but occasionally the pressure sensor itself has failed and is reporting incorrectly even when the system is fine — worth checking the actual gauge reading against what the boiler reports.
Can any Gas Safe engineer work on a Vaillant boiler under warranty?
For routine repairs and servicing, any Gas Safe registered engineer with appropriate experience can work on a Vaillant boiler without affecting the manufacturer’s warranty, provided the work is carried out competently and genuine or compatible parts are used. It’s only new installations and certain extended warranty products that specifically require a Vaillant-accredited installer, so an existing boiler’s ongoing repairs aren’t restricted to Vaillant-approved engineers only.
Is it worth fitting a magnetic filter to a Vaillant system?
Yes, particularly on a system without one already, since a magnetic filter catches debris and sludge before it reaches the boiler’s heat exchanger — one of the more common sources of long-term wear and fault codes on any brand, including Vaillant. It’s a relatively small one-off cost compared with the heat exchanger repairs it can help prevent over the boiler’s lifetime.
Related fault-code guides
Book a Vaillant repair, or see the full fault code library for other brands. We service Vaillant boilers across Finchley, Barnet and Camden, plus the rest of our coverage area. Prevent most of these faults with annual servicing.
Got a Vaillant fault code showing?
Call us with the exact code and we’ll tell you honestly what it means — and what it will cost to put right.
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