Vaillant boiler error codes are the diagnostic messages your boiler displays whenever it detects a fault, whether that’s low water pressure, an ignition failure, a sensor issue, or a genuine overheating event, and each one points to a specific part of the system that needs attention.
Some faults, like low pressure, can often be fixed safely at home in a few minutes, while others, such as a gas valve or circuit board fault, always need a Gas Safe registered engineer.
This guide brings together every common Vaillant fault code in one place, explains what each one actually means, and gives you the first steps to take for each one.
Vaillant Boiler Error Codes: Full Reference Table
The table below lists the broader range of Vaillant fault codes you may come across, including some less common ones not covered in detail above.
| Code | What It Generally Means |
| F.00 / F.01 | Flow or return temperature sensor interruption |
| F.10 / F.11 | Short circuit of the flow or return NTC sensor |
| F.20 | Temperature limiter safety switch activated |
| F.22 | Low water pressure safety switch-off |
| F.23 | Flow and return temperature difference too great |
| F.24 | Temperature increasing too rapidly |
| F.25 | Flue gas temperature too high |
| F.26 | Gas valve fault |
| F.27 | Flame simulation detected |
| F.28 | Ignition not established at startup |
| F.29 | Flame lost during operation |
| F.32 | Fan speed fault |
| F.49 | Potential short circuit or eBUS communication error |
| F.54 | Insufficient gas supply |
| F.61 | Gas valve actuation or regulation problem |
| F.62 | Gas valve switch-off delay |
| F.63 | EEPROM memory problem |
| F.64 | Electronics or NTC sensor fault |
| F.65 | Electronic temperature overheating |
| F.67 | Electronics flame signal issue |
| F.72 | Flow and return NTC implausible difference |
| F.75 | No pressure change detected at pump start |
| F.76 | Heat exchanger overheat protection tripped |
| F.83 | Dry fire detection, flow and return temperature fault |
| F.84 | Flow and return sensor values inconsistent |
Common Vaillant Boiler Fault Codes Explained
Below is a breakdown of the most frequently reported Vaillant boiler fault codes, what each one means, and the first steps to take. Each summary links through to a full guide covering the specific causes behind that code in more depth.
F4 Error Code: Ignition Fault
The Vaillant F4 error code means your boiler failed to establish a flame during ignition and has locked out. Common causes include an interrupted gas supply, a frozen condensate pipe, a worn ignition electrode, or a faulty flame sensor.
How To Fix
- Check your gas meter is switched on and has sufficient credit if it’s a prepayment type.
- Check outside for a frozen condensate pipe and thaw it gently with warm water if needed.
- Reset the boiler once and allow it to complete a full ignition attempt.
- If the fault returns, stop resetting and book a Gas Safe registered engineer to check the ignition electrode, flame sensor, and gas valve.
F22 Fault Code: Low Water Pressure
The Vaillant F22 fault code is a low water pressure lockout, meaning there isn’t enough water in your sealed heating system to operate safely. This is one of the easiest faults to resolve yourself using your boiler’s filling loop.
How To Fix
- Check your pressure gauge and confirm it’s reading below 1.0 bar.
- Use the filling loop to top up pressure slowly to between 1.0 and 1.5 bar.
- Close both filling loop valves firmly and reset the boiler.
- If pressure keeps dropping over the following days, book a Gas Safe engineer to trace a possible leak.
F23 Fault Code: Excessive Flow And Return Temperature Difference
The F23 fault code on your Vaillant boiler means the temperature gap between the flow and return pipes has grown too large, usually pointing to poor circulation caused by sludge, a weak pump, or trapped air.
How To Fix
- Check for cold spots at the bottom of radiators, which can indicate sludge.
- Bleed your radiators to clear any trapped air, then top up pressure if needed.
- Reset the boiler once and monitor whether it runs a full cycle without cutting out.
- If the fault persists, book a Gas Safe engineer to check the pump and assess whether a power flush is needed.
F24 Fault Code: Temperature Rising Too Fast
The F24 fault code on a Vaillant boiler is triggered when water temperature rises faster than it safely should, which almost always comes down to restricted circulation from closed valves, trapped air, low pressure, or a failing pump.
How To Fix
- Check that the isolation valves underneath your boiler are fully open.
- Bleed your radiators to release any trapped air and top up system pressure if it’s low.
- Reset the boiler and check whether it completes a heating cycle normally.
- If F24 returns, book a Gas Safe engineer to test the circulation pump and check for sludge.
F25 Fault Code: Flue Gas Temperature Too High
The F25 fault code means flue gas temperature has climbed too high, or the sensor monitoring it has developed a wiring fault. It’s frequently linked to the same circulation problems behind F23 and F24.
How To Fix
- Allow the boiler to cool fully for twenty to thirty minutes before doing anything further.
- Check and top up system pressure if it’s reading below 0.8 bar.
- Attempt a single reset once the boiler has cooled and pressure looks correct.
- If the fault returns, do not reset again. Book a Gas Safe engineer to check the pump, look for sludge, and test the flue gas sensor wiring.
F26 Fault Code: Gas Valve Fault
The F26 fault code points to a fault with the gas valve or its stepper motor, preventing the boiler from correctly metering gas for ignition. This is a safety critical fault that always needs a Gas Safe engineer.
How To Fix
- Check your gas supply is on and test another gas appliance to rule out a wider supply issue.
- Confirm the emergency control valve near your meter is fully open.
- You can attempt a single reset, but do not repeat this if the fault returns.
- Book a Gas Safe engineer to test the stepper motor, wiring, and gas valve directly.
F27 Fault Code: Flame Simulation
The F27 fault code is the reverse of most ignition faults, since it means the boiler is detecting a flame signal when there shouldn’t be one. It’s commonly caused by moisture on the flame sensing electrode or a gas valve that isn’t sealing fully.
How To Fix
- Attempt a single reset, since brief condensation can sometimes cause a one-off false reading.
- Check the area around and beneath your boiler for any signs of damp or leaks.
- Avoid repeated resets if the fault returns, since this won’t resolve a genuine moisture or valve issue.
- Book a Gas Safe engineer to test the ionisation current, flame sensing electrode, and gas valve sealing.
F28 Fault Code: Ignition Failure On Startup
The F28 fault code means your Vaillant boiler attempted to ignite but failed to detect a flame within its safety window. Gas supply issues and frozen condensate pipes together account for the majority of these lockouts.
How To Fix
- Check your gas meter is switched on and has sufficient credit.
- Check outside for a frozen or blocked condensate pipe and thaw gently with warm water if frozen.
- Reset the boiler once and observe the full ignition sequence.
- If F28 returns, book a Gas Safe engineer to check the ignition electrode, flame sensor, and gas valve.
F29 Error Code: Flame Loss During Operation
The F29 error code means your Vaillant boiler successfully lit but then lost the flame partway through a heating cycle. Causes range from a frozen condensate pipe to a dirty flame sensor or a failing gas valve.
How To Fix
- Check your gas supply and test another gas appliance to rule out a wider issue.
- Check outside for a frozen condensate pipe and thaw it gently if needed.
- Reset the boiler once and monitor whether it stays running through a full cycle.
- If F29 returns, book a Gas Safe engineer to check the flame sensor, flue, and gas valve.
F32 Fault Code: Fan Error
The F32 fault code means your Vaillant boiler’s fan is running outside its expected speed range, often due to a worn fan motor, a blocked flue, or a faulty Hall sensor.
How To Fix
- Check the external flue terminal for any visible blockages such as leaves, nests, or debris.
- Confirm any air vents in the room housing your boiler haven’t been accidentally covered.
- Attempt a single reset and allow the boiler a couple of minutes to complete start-up.
- If the fault returns, book a Gas Safe engineer to test the fan motor and Hall sensor.
F54 Fault Code: Insufficient Gas Supply
The F54 fault code indicates your Vaillant boiler isn’t receiving enough gas flow or pressure to ignite. It often appears alongside F28 or F29, since all three can share the same root cause.
How To Fix
- Check every gas stopcock and the emergency control valve near your meter is fully open.
- Confirm your prepayment meter has sufficient credit if applicable.
- Test another gas appliance to see whether it’s also affected.
- If the fault persists after these checks, book a Gas Safe engineer to test the internal gas valve and check incoming pressure.
F61 Fault Code: Gas Valve Actuation Fault
The F61 fault code on Vaillant boiler means the control board cannot properly actuate or confirm the gas valve, usually due to damaged wiring, a worn valve, or a fault within the PCB itself.
How To Fix
- Attempt a single reset to rule out a one-off glitch.
- Do not repeat the reset if the fault returns.
- Book a Gas Safe engineer to test the wiring harness, gas valve resistance, and PCB driver circuit.
- Mention any recent servicing or repair work, since this can help narrow down when the fault developed.
F62 Fault Code: Delayed Flame Switch-Off
The F62 fault code means the flame took too long to switch off after the burner was told to stop, pointing to a defective gas valve, PCB, or ignition electrode.
How To Fix
- Turn off the gas supply to your boiler at the isolation valve as a precaution.
- Do not attempt to open the boiler casing yourself.
- You can try one reset, but avoid repeating this more than once.
- Book a Gas Safe engineer to test the gas valve, PCB, and ignition electrode.
F72 Fault Code: Flow And Return Sensor Error
The F72 fault code means the flow and return NTC sensors are reporting an implausible temperature difference, most often due to a defective sensor, damaged wiring, or poor circulation.
How To Fix
- Check your system pressure and top it up if it’s reading low.
- Bleed your radiators if you notice cold tops and warm bottoms, which can indicate trapped air.
- Attempt a single reset once these checks are complete.
- If the fault persists, book a Gas Safe engineer to test both NTC sensors and the wiring connecting them to the PCB.
F75 Fault Code: No Pressure Change Detected
The F75 fault code appears when your Vaillant boiler doesn’t detect an expected pressure change as the pump starts, commonly caused by a faulty pressure sensor or a failing pump.
How To Fix
- Check your pressure gauge with the heating off for at least an hour and top up if it reads below 1.0 bar.
- Reset the boiler and check whether the fault clears once pressure is corrected.
- If pressure is already correct and the fault persists, avoid repeated resets.
- Book a Gas Safe engineer to test the water pressure sensor and circulation pump.
F76 Fault Code: Overheat Protection Tripped
The F76 fault code means the safety fuse on the primary heat exchanger has tripped due to genuine overheating, usually triggered by sludge, a failing pump, or trapped air restricting flow.
How To Fix
- Check your pressure gauge and top up if it’s reading low.
- You can attempt one reset, but do not repeat this if the fault returns immediately.
- Book a Gas Safe engineer, since the physical safety fuse will likely need replacing by a professional.
- Ask the engineer to check for sludge, pump performance, and trapped air as part of the same visit.
F83 Fault Code: Dry Fire Detection
The F83 fault code means your Vaillant boiler didn’t detect the expected temperature rise after the burner started, often linked to low water content, trapped air, or a faulty sensor.
How To Fix
- Check your pressure gauge and top up using the filling loop if it’s low.
- Bleed your radiators to clear any trapped air affecting circulation.
- Reset the boiler once these checks are complete.
- If the fault persists, book a Gas Safe engineer to test the flow and return sensors and check for sludge.
F84 Fault Code: Flow And Return Sensors Disagree
The F84 fault code means the flow and return sensors are giving contradictory readings, frequently caused by the sensors being fitted the wrong way round or a circulation fault.
How To Fix
- This fault cannot be diagnosed or fixed without opening the boiler casing, so avoid attempting any internal checks yourself.
- Note whether your boiler has had any recent servicing or pipework changes, as this can help identify the cause.
- Book a Gas Safe engineer to confirm the sensors are fitted to the correct pipes and test their accuracy.
- Ask the engineer to check the pump and any valves if sensor positioning turns out to be correct.
How to Reset a Vaillant Boiler After a Fault Code?
You can reset most Vaillant boilers by locating the reset button, usually marked with a flame symbol with a line through it, and pressing and holding it for around three seconds.
Before resetting, it’s worth checking that your gas stopcock is fully open and that your system pressure looks normal on the display gauge, since both of these are common and easily fixed causes behind several fault codes.
Once you’ve reset the boiler, allow it a minute or two to complete its full start-up sequence and confirm whether the fault has cleared.
As a general rule, it’s fine to attempt one reset to see if a fault clears, but you should avoid resetting repeatedly if the same code keeps returning, since this can mask a genuine underlying problem and, in some cases, place additional strain on components that are already failing.
When Should You Call a Gas Safe Engineer Instead Of Resetting Your Boiler?
You should call a Gas Safe registered engineer whenever a fault code returns after a single reset attempt, or whenever the fault relates to gas valves, wiring, sensors, or the printed circuit board rather than something as simple as low pressure.
Vaillant itself is clear that any error code displayed on the unit requires professional assistance to resolve properly, since these codes exist specifically to prevent unsafe operation.
Continuing to reset a boiler repeatedly, particularly one showing a gas valve or overheat related code, can mask a genuine safety issue and, in some cases, allow underlying wear to worsen until a more significant repair is needed.
Boiler Faults Becoming A Regular Occurrence? Get A Free Quote From Clever Energy Boilers
If you find yourself looking up fault codes on a fairly regular basis, it’s worth stepping back and considering what that pattern is actually telling you about your boiler’s condition.
A boiler that only occasionally needs a pressure top-up is behaving normally, but one that’s cycling through different fault codes every few months, whether that’s ignition faults one visit and sensor faults the next, is very often a sign that multiple components are ageing and wearing out together rather than one isolated part being at fault.
Many boilers keep running past 10 years. By around 8 years old, though, efficiency has usually dropped and faults become more common. At that age, a new boiler is often better value than paying callout fees and parts for one repair after another.
At Clever Energy Boilers, we install reliable, efficient boilers for homeowners and landlords across the North West, Yorkshire, and the Midlands, helping people move on from a boiler that keeps throwing up fault codes and into a system that simply works.
Request your free, no-obligation boiler quote today.
A new boiler installation means every component, from the gas valve to the sensors to the control board, is fresh, correctly calibrated, and backed by a long warranty through Clever Energy, along with meaningfully better efficiency than an older unit, which often makes a genuine difference to your energy bills.
Repairs are a job for a Gas Safe registered engineer. Our role is supplying and fitting new boilers, and a free quote shows you exactly what a replacement would cost.
Frequently Asked Questions
What Do Vaillant Boiler Error Codes Mean?
Vaillant boiler error codes mean your boiler has detected a specific fault somewhere in the system and has locked itself out rather than continue operating unsafely. Every Vaillant boiler, from the ecoTEC Pro and Plus ranges through to older turboTEC and atmoTEC models, is built with a series of internal sensors constantly monitoring gas flow, water pressure, flame presence, and temperature.
The moment any of these readings fall outside a safe range, the control board displays a corresponding F-code on the boiler’s screen and shuts the system down, protecting both your home and the boiler itself from potential damage. Codes generally fall into a few broad categories: pressure and circulation faults, ignition and flame faults, gas valve faults, sensor and wiring faults, and overheat or safety limiter faults.
Why Does My Vaillant Boiler Show A Different Fault Code Every Time?
A Vaillant boiler showing a different fault code each time it breaks down often indicates that several components are reaching the end of their working life around the same time, rather than one single part repeatedly failing. This is particularly common in older boilers, where sensors, valves, and mechanical parts have all been through the same years of wear. Once a boiler is over 8 years old, it’s usually less efficient too, so a new boiler is usually the best option.
Can I Look Up My Exact Boiler Model To Check Which Fault Codes Apply?
Yes, you can find your exact Vaillant boiler model and serial number on the data badge, usually located on the inside of the front panel or on a sticker on the casing itself. While most F-codes apply broadly across the ecoTEC range, checking your specific model against Vaillant’s official documentation can help confirm the precise meaning for older or less common boiler types.
Does A Fault Code Always Mean Something Is Broken?
Not necessarily. Some fault codes, particularly low pressure related ones like F22, are often triggered by something straightforward, such as recently bled radiators or natural pressure loss over time, rather than a genuinely broken component. Other codes, especially those relating to gas valves, overheat protection, or circuit boards, are more likely to indicate an actual component fault requiring repair.
How Long Can I Leave My Boiler Showing A Fault Code Before Getting It Looked At?
You shouldn’t leave a boiler displaying a fault code unaddressed for an extended period, particularly during colder months when losing your heating and hot water becomes a more pressing issue. Beyond the inconvenience, some faults, especially those relating to gas valves or overheating, can potentially worsen the longer they’re left without proper diagnosis and repair.
Is It Worth Getting An Annual Service To Avoid Fault Codes?
Yes, an annual service is one of the most effective ways to reduce the likelihood of unexpected fault codes, since a qualified engineer can identify early signs of sludge build-up, sensor drift, or component wear before they escalate into a full lockout. Regular servicing also helps keep any existing warranty valid, which can save you money if a genuine component fault does develop.