Vaillant Boiler Error Codes: What F22, F28, F75 and the Rest Mean

Your Vaillant has flashed an F-code and gone quiet. Here's what the common ones mean, what's safe to try yourself, and when to leave it to a Gas Safe engineer.

Picture the scene. It's a cold evening, the house has gone quiet in that unsettling way, and the little screen on your Vaillant says F.28. No hot water, no heating, and a code that means nothing to you.

Most Vaillant fault code lists online are long tables of numbers with a one-line cause beside each. Useful if you already know what you're doing. Less useful at 7pm with cold hands. So this guide does something different: it tells you which codes you can safely look into, which ones you shouldn't touch, and what to do in the ten minutes before you pick up the phone.

Vaillant boilers, including the popular ecoTEC range, display faults as an F followed by a number. The boiler is not broken just because a code appears. Most of the time it has spotted something and shut itself down on purpose.

Key takeaways

• F22 is the one most homeowners can help with, because it is usually low pressure.
• F28 and F29 are often gas, ignition or frozen condensate pipe problems. Check the basics, then reset once.
• Overheating, fan, flue, sensor and gas valve codes are for a Gas Safe engineer only.
• Meanings can differ slightly between models. Your manual wins.
• Gas smell or carbon monoxide symptoms: leave and call 0800 111 999.

First: is this an emergency?

Smell gas? Act now, read later.

• Open doors and windows and leave the property.
• Don't switch lights or appliances on or off. No flames.
• If you can reach it safely, turn the gas off at the meter.
• Call the National Gas Emergency Service on 0800 111 999 (free, 24 hours) from outside.

No gas smell? Here is how we sort the codes below:

Do this first, whatever the code

1. Photograph the display. Note the exact F-code and your model name (it is on the front or data plate, for example ecoTEC plus). It saves a lot of back-and-forth with an engineer.
2. Check the pressure gauge. When the system is cold, it should sit at roughly 1 to 1.5 bar. Lower than 1 bar and a Vaillant will often refuse to run.
3. Check the basics. Is there power? Are the thermostat and timer calling for heat, with working batteries? Does the gas hob work? Is there credit on a prepayment meter?
4. Reset it once. Details below. If the code stays gone, good.
5. Code back? Stop. Repeated resets only repeat the fault. Time for a professional.

Have boiler or home emergency cover? Call your provider before you book an engineer yourself. With Smart Cover, repairs arranged without our approval may not be covered.

The four Vaillant codes people search for most

F22: low pressure

The boiler has noticed the water pressure is too low, or there isn't enough water. It is common after bleeding radiators and a regular autumn visitor.

Try: top up with the filling loop to about 1 to 1.5 bar, following your manual.

Stop if: it drops again within days. That suggests a leak.

F28: failed to ignite

The boiler tried to light and couldn't. The usual suspects are a gas supply issue, an empty prepayment meter, or in a frost, a frozen condensate pipe.

Try: check the gas hob and meter, check the gas valve is open, thaw a frozen condensate pipe with warm (not boiling) water, then reset once.

Stop if: it repeats. Ignition parts need an engineer.

F29: flame lost

The boiler lit, then the flame dropped out, or it couldn't relight. The causes overlap with F28, plus things like a dirty burner or flue problems.

Try: the same basic checks as F28 and one reset.

Stop if: it comes back, especially with odd noises or smells.

F75: pump or pressure sensor

The boiler expected the pressure to change when the pump started, and it didn't. That points at the pump, the water pressure sensor, or trapped air.

Try: check the gauge is not low, and reset once.

Stop if: it returns. Don't keep topping up the pressure. Call an engineer.

Vaillant fault code table

Vaillant uses a lot of codes, and the exact wording varies by model, so this table groups the common ones by type. It's a starting point, not a replacement for your manual.

Meanings are common interpretations for typical Vaillant boilers and vary by model. Where your display shows a code not listed here, use the manual or ask an engineer.

Spot the pattern: the green codes are about pressure, gas and ignition. Everything with a fan, a sensor, a pump or heat in it is amber.

How to reset a Vaillant boiler

On most Vaillant models, press and hold the reset button on the control panel for a few seconds until the display clears, then release and let the boiler restart. Some models have a slightly different procedure, so check your manual if the button isn't obvious.

The rule is once. A reset clears a lockout so the boiler can try again. If the cause was a blip, it carries on happily. If the cause is real, the code returns, and that is useful information, not a reason to keep pressing the button.

When to stop and call a Gas Safe engineer

Boilers are sealed gas appliances, and in the UK gas work must be done by someone on the Gas Safe Register. Call when:

• a code comes back after one reset, or a different one replaces it
• it relates to the fan, flue, sensors, pump, overheating or gas valve
• there is leaking water, banging or whistling, soot or black marks around the boiler
• the flame, if you can see it, looks mostly yellow or orange rather than steady blue
• fixing it would mean taking the casing off. Always.

Check the ID. Every registered engineer carries a Gas Safe ID card with a photo, and you can verify them on the Gas Safe Register website. If you have boiler cover, call your provider first so they can arrange the engineer.

Carbon monoxide: the quiet one

Carbon monoxide has no smell, colour or taste. Symptoms feel like flu without a temperature: headaches, dizziness, nausea, tiredness. If several people at home feel unwell and it eases when you're out, take it seriously. Fit an audible CO alarm near the boiler and in bedrooms, test it, and if it sounds, open windows, leave and call 0800 111 999.

Why Vaillant codes spike in cold weather

Colder months bring more fault codes for a few reasons. A frozen condensate pipe can cause ignition-type faults (F28, F29). A system that has sat idle all summer may show low pressure (F22) or a sticky pump. And demand goes from nothing to everything overnight.

• Glance at the pressure gauge once a month.
• Bleed radiators that are cold at the top.
• Book an annual boiler service to catch small faults early. If you have Smart Cover boiler cover, your boiler must have been serviced in the 12 months before a breakdown claim.
• If you’re counting the cost of running it, a well-maintained boiler with correct pressure and bled radiators runs more efficiently.

If your Vaillant is getting on and the codes keep changing, it’s worth calmly weighing up whether to keep repairing it or replace it. A Gas Safe engineer can give you an honest view of its condition.

Vaillant lockout at the worst moment?

Smart Cover boiler cover and home emergency cover are there for the covered breakdowns the checklist can't fix. Report an emergency any time on our 24/7 Emergency Helpline, 03333 449 247, and we'll arrange an engineer from our UK network for covered faults. For claims and other enquiries, call 03333 449 559.

Before you rely on cover, know the key terms:

• Cover is for gas boilers only. Oil, LPG and electric boilers are not covered.
• Your boiler must have been serviced in the 12 months before a breakdown claim.
• There is a waiting period from the start of your policy: 14 days for homeowner policies and 28 days for landlord policies.
• Claims are paid up to the claim limit on your policy schedule.
• Exclusions include wear and tear, sludge and limescale, faults that existed before your policy started, and repairs arranged without contacting us first.

See boiler cover or home emergency cover. Read the policy documents and IPID for full terms. Cover helps with repair costs for covered breakdowns. A gas smell or CO symptoms are always an emergency call to 0800 111 999 first.

Official sources

• Gas Safe Register: find and check registered engineers
• HSE: gas safety in the home
• National Gas Emergency Service: 0800 111 999
• Your Vaillant manual or Vaillant's own website for model-specific fault code lists

General information only. This guide isn't a substitute for your boiler manufacturer's instructions or advice from a Gas Safe registered engineer. Fault code meanings vary by model. Smart Cover is not affiliated with Vaillant. This is a marketing communication. Cover is subject to policy terms, limits and exclusions. Reviewed 11 November 2026.

Smart-Cover Insurance Services, Smart Cover and Smart Cover 247 are trading names of Smart-Cover Direct Limited (FRN 600428), an Appointed Representative of City and Commercial Limited (FRN 314346), which is authorised and regulated by the Financial Conduct Authority. The Financial Ombudsman Service can be contacted at www.financial-ombudsman.org.uk.