F28 Vaillant Boiler Error Code: How To Fix & Causes

The Vaillant F28 error code means your boiler has failed to ignite after three attempts.

Common reasons for the F28 boiler fault code include low water pressure, gas supply interruptions, a frozen condensate pipe, faulty gas valve or ignition parts, or wiring/PCB faults.

You can try resetting your boiler and checking pressure or thawing pipes, but persistent problems require a Gas Safe engineer. Prompt professional repairs keep your boiler safe, efficient, and warranty-valid.

What Does the F28 Error Code Mean on a Vaillant Boiler?

The Vaillant F28 error code indicates the boiler has attempted to ignite three times but failed, triggering a safety lockout to prevent gas buildup or damage. This fault appears on models like the Vaillant ecoTEC Pro, ecoTEc Plus and Turbomax Plus series.

The core issue is that ignition has failed, meaning gas isn’t lighting to heat water for your taps and radiators.

The causes fall broadly into ignition faults (spark or flame sensing failures), gas valve problems, or external gas supply issues. This fault often happens during cold weather when demand is high or a condensate pipe freezes.

Boiler Not Igniting

The F28 fault is Vaillant’s specific code for “boiler not igniting.” Your system tries three times to light the burner but doesn’t detect a flame. This can be due to ignition electrodes failing to spark or sense flame, mechanical gas valve faults restricting gas flow, or supply interruptions.

You may hear clicking from the ignition system before the code appears, signalling failed spark attempts.

Low Water Pressure

Low system pressure is a frequent cause of ignition failure. The boiler prevents firing if pressure drops below 0.5 bar, which might happen due to leaks, radiator bleeding, or temperature changes.

To repressurise:

• Turn off the boiler.
• Connect the filling loop and open valves slowly until pressure reaches 1.0 to 1.5 bar.
• Close valves and remove the loop.

If pressure drops again soon, you may have a leak requiring professional attention.

Gas Supply Issues

Yes. Confirm your gas supply is active by testing other gas appliances. Problems with prepayment meters, regional outages, or supply restrictions can cause ignition failures. If all other appliances work but the boiler faults, the problem lies internally.

Also, environmental factors such as debris blocking gas flow or faulty pressure regulators rarely cause F28 errors but should be checked by an expert.

Frozen Condensate Pipe

A common winter culprit, the condensate pipe can freeze and block vital drainage. This blockage triggers the boiler’s safety features, causing an F28 fault.

To thaw a frozen condensate pipe:

• Use warm (not boiling) water poured slowly over the pipe.
• Alternatively, apply a warm cloth or hot water bottle.

Avoid boiling water to prevent burns or damage.

If thawing clears the fault, monitor the pipe and consider insulation to prevent recurrence.

Faulty Flame Sensor or Ignition System

Yes. Ignition electrodes spark to light the burner. The flame sensor detects the flame’s presence. Carbon deposits or damage can prevent proper function, causing shutdowns.

Replacing or cleaning these parts usually requires a Gas Safe engineer. DIY attempts risk further damage or warranty voiding.

Can I Reset My Vaillant Boiler to Fix the F28 Fault?

Yes, you can reset your Vaillant boiler, but only as a troubleshooting step:

• First, check the boiler pressure gauge reads between 1.0 and 1.5 bar.
• Locate and press the reset button—often marked with a flame symbol—for 3 to 5 seconds.
• Wait to see if the boiler fires up successfully.

If the fault returns quickly, avoid repeated resets. Overusing reset without fault diagnosis may damage components and delay proper repair. Resets do not fix underlying issues like faulty valves or ignition parts.

Call a Gas Safe Engineer

Contact a professional if:

• The F28 fault persists after resetting, repressurising, and thawing pipes.
• You smell gas or suspect a leak.
• You suspect electrical faults in wiring or the PCB.
• Your boiler is older and frequently developing faults.

Only Gas Safe-registered engineers can safely diagnose and repair gas appliances, which is a legal requirement.

Will My Vaillant Warranty Cover F28 Fault Repairs?

Your Vaillant warranty covers manufacturing defects related to F28 when repairs are done by approved engineers. To keep the warranty valid:

• Have your boiler serviced annually by Vaillant-approved engineers.
• Avoid DIY repairs on regulated components.
• Keep maintenance records.

Poor maintenance or unapproved repairs may void the warranty.

How Can I Prevent Future F28 Errors?

Maintain regular service appointments. Check system pressure monthly and bleed radiators carefully. Insulate condensate pipes before winter and consider installing magnetic filters and inhibitors to reduce sludge and corrosion. For ageing boilers, upgrading to newer models may improve reliability and efficiency.

What Does Repair Typically Cost?

Repair costs vary but expect:

• Gas valve replacement: approximately £300 including labour.
• Ignition electrode or sensor replacement: £25–£80.
• Call-out and diagnosis fees depend on your region and urgency.

Addressing issues early avoids more costly repairs and service interruptions.

The Vaillant F28 error code means your boiler can’t ignite—usually after three failed attempts—so it shuts down for safety. This often happens because of low water pressure, a frozen pipe, problems with the gas supply, or faults in the boiler’s ignition parts.

Some basic checks—like topping up the pressure or thawing the condensate pipe—might get you warmed up again, but more complex issues (such as faulty wiring or a broken gas valve) need a Gas Safe engineer. It’s always best to get help fast to avoid cold showers and keep your warranty valid.​

FAQs

What does the F28 error code mean?

The F28 code tells you your Vaillant boiler failed to light the burner, so it’s gone into safety lockout. This can happen after three failed ignition attempts and stops the boiler giving you hot water or heat.​

Can I fix the F28 error myself?

Sometimes! If the problem is low pressure, you can top up the boiler using the filling loop (just make sure the pressure gauge reads 1.0–1.5 bar). If it’s a frozen pipe, pour warm (not boiling) water over the condensate pipe to thaw it. Always restart the boiler after checking these. If you smell gas, or your fixes don’t work, call a Gas Safe engineer straight away.​

Why does my boiler show F28 and not light?

The most common causes are low pressure, a frozen condensate pipe, no gas to your home, a stuck gas valve, or problems with the ignition system. Older boilers and cold weather make this more likely. Try basic checks above, and if you’re unsure, get a pro to take a look.​