Vaillant boiler fault codes — what they mean and what to do

What your Vaillant fault code is telling you

Your Vaillant boiler shows a fault code when something isn't right. It's an F-code on the display, like F.22 or F.28. The boiler hasn't broken for good. It's stopped itself to stay safe.

Some codes point to a quick fix you can do yourself. Low pressure is the classic one. Others mean a part has failed and you'll need a Gas Safe registered engineer to look at it.

Below we've listed the most common Vaillant ecoTEC codes, what each one means, and what to do next. We've kept the advice safe and honest. If a code involves gas, don't touch it — call the experts.

Smell gas at any point? Stop. Open the windows, turn off the gas at the meter, and leave the property. Then call the National Gas Emergency Service on 0800 111 999. Don't flick any electrical switches. Don't try to fix gas yourself.

Common Vaillant fault codes at a glance

F.22 — low water pressure

F.22 is the most common Vaillant code, and the good news is it's often a quick fix. It means the water pressure in your system has dropped too low for the boiler to run safely.

Look at the pressure gauge on the front. If the needle's below 1 bar, you can usually top it up yourself using the filling loop — that's the small silver braided hose under the boiler.

Open both valves on the loop slowly until the gauge reads about 1 to 1.5 bar when the boiler is cold, then close them again. Reset the boiler and you should be back to normal.

If the pressure keeps dropping after you top it up, you've likely got a leak somewhere. That needs a Gas Safe registered engineer to track down and fix.

F.28 and F.29 — ignition problems

F.28 means your boiler tried to fire up but couldn't ignite. F.29 means the flame lit but then went out and wouldn't relight. They often share the same causes.

Before you call anyone, run a few safe checks. Is the gas on? Try lighting a gas hob — if that won't light either, the problem is your gas supply, not the boiler. On a pre-payment meter, check you've got credit.

In cold weather, a frozen condensate pipe is a common cause. That's the white plastic pipe running outside to a drain. If it's blocked with ice, the boiler can't get rid of waste and locks out.

If the gas is on, there's no ice, and the boiler still won't fire, stop there. Ignition faults usually mean a failed part — book a Gas Safe registered engineer to sort it.

F.62 — gas valve fault (do not DIY)

F.62 means the gas valve isn't shutting off when it should. Your Vaillant detects this and locks out to keep you safe.

There's nothing safe to try yourself here. Anything to do with the gas valve must be handled by a Gas Safe registered engineer — it's the law, and it's the right call.

Don't keep resetting a boiler showing F.62. Book an engineer. If you ever smell gas, call 0800 111 999 straight away.

Safe checks before you call someone out

A few of these can get your boiler going again without a call-out. Only do what's on this list — never attempt anything involving gas.

• Check the pressure gauge — if it's below 1 bar, top up with the filling loop to 1 to 1.5 bar when cold.
• Reset the boiler once using the reset button. If it locks out again, leave it and call an engineer.
• Check your thermostat is on, set high enough, and has working batteries.
• Make sure the gas is on — try a gas hob. If it won't light, the issue is your supply.
• On a pre-payment meter, check you've got credit.
• In freezing weather, check the outside condensate pipe isn't frozen — a warm (not boiling) flask of water poured over it can thaw it.
• Check the boiler's power supply and that no fuses have tripped.
• If you smell gas, stop everything — open the windows, turn off the gas at the meter, leave the property and call 0800 111 999. Don't flick switches.

How Smart Plan helps when it's not a DIY fix

If you've done the safe checks and your Vaillant still won't play ball, that's where we come in. We'll come and fix it for you.

You've got two ways to do this. Book a one-off repair and we'll send a Gas Safe registered engineer out to diagnose and fix the fault. Or take out ongoing cover so you're sorted next time too.

Cover that's built around you

Smart Plan is modular. You pick only the modules you want and don't pay for what you don't use. Most homes start with the boiler module and build from there.

Parts and labour are included up to your cover limit. For boilers under 7 years old that's up to £500 in a 12-month period; up to £200 for boilers over 7 years. There's a £95 call-out fee. Most other modules cover up to £500 per year, with up to £225 per appliance.

Is this insurance?

No. Smart Plan is a service plan, not insurance. The promise is simple — when something breaks, we'll come and fix it for you.

We've been trading since 2014, we look after over 15,000 customers, and we're rated Excellent on Trustpilot. Our work is carried out by a network of Gas Safe registered engineers.

Vaillant fault code FAQs

Boiler still showing a fault code?

Don't sit in the cold. Whether it's a one-off repair or ongoing cover, we'll come and fix it for you. Smart Plan is a service plan, not insurance — modular cover with parts and labour included up to your limit.

Helpful links

• No heating? Book a repair
• Boiler & central heating cover
• More guides on the Smart Plan blog
• Check an engineer on the Gas Safe Register