Vaillant Boiler Fault Codes: What Your ecoTEC Is Saying

Vaillant boiler fault codes mean your boiler has stopped, or held itself back, to protect itself or you. Codes starting with F are faults. Codes starting with S are normal status messages. On an ecoTEC, the usual suspects are F.22 (low pressure), F.28 and F.29 (ignition), and F.75 (pump or pressure sensor). Several you can check safely yourself.

Codes tend to appear at the worst moment: a freezing morning, a full house, or a tenant texting to say the hot water's gone. It's tempting to keep pressing reset, or to order whichever part a forum post blames.

The catch is that a code describes a symptom, and one symptom can have three or four causes. F.22 might be a harmless dip after bleeding radiators, or a slow leak under the floorboards. Guess wrong and you pay for parts you didn't need. Keep resetting an ignition code and you're forcing the boiler to retry something it has flagged as unsafe.

What Are Vaillant Boiler Fault Codes Trying to Tell You?

A fault code means your boiler has spotted something outside its safe limits, so it has stopped or held back until that's sorted. The same display that shows your 21°C setting is where these codes appear.

Vaillant uses two kinds of code. Codes starting with F are faults. Codes starting with S are status messages that show what the boiler is doing, so they aren't faults at all. On most ecoTEC plus models, S.4 means the burner is lit. S.7 means the pump is running on after the heating has switched off, moving leftover heat around the system. A boiler showing S.7 isn't broken.

What you see depends on your model's age. Newer touchscreen models show the code with a short text description. Older ecoTEC models show only the code, sometimes next to a spanner or flame symbol. F codes are broadly consistent across the ecoTEC plus, pro and exclusive ranges. Wording and behaviour can still vary by model and age, so check the code against your own manual.

Keep one idea in mind as you read on. A code tells you what the boiler noticed, and several different faults can trigger the same warning. That's why swapping parts on a guess so often wastes money.

Before you do anything else, take a photo of the display. Then jot down:

• the reading on the pressure gauge
• what was happening at the time, such as heating on, a hot tap running or a cold snap
• whether this is the first time or the code keeps coming back

An engineer will find this useful, and it often speeds up the diagnosis.

Safety first. If you smell gas, don't use light switches or anything electrical. Turn off the gas at the meter if it's safe to do so, open the windows, leave the property and call the National Gas Emergency Service on 0800 111 999 (free, 24 hours). If your carbon monoxide alarm goes off, get everyone outside and keep the boiler off until a Gas Safe engineer has checked it. Vaillant strongly advises against getting inside your boiler, so never take the casing off.

For a wider look at alarms and gas appliances around the home, see our London home gas safety checklist.

The Vaillant ecoTEC Fault Codes You're Most Likely to See

Most callouts come down to a handful of codes. F.22 means low pressure, F.28 and F.29 are ignition or flame problems, and F.75 is a pump or pressure sensor fault. The rest mostly point to sensors, the fan, the controls or the electronics.

The meanings below follow Vaillant's own fault code list, put into plain English.

It's easier to spot patterns if you group the codes into three families:

• Water and circulation: F.20, F.22, F.23, F.24 and F.75
• Ignition and flame: F.27, F.28 and F.29
• Sensors, fan, controls and electronics: F.0, F.1, F.32, F.49 and F.61 to F.64

Only the water and circulation family, plus F.28 and F.29, usually has anything you can safely check at home. The sensor, fan, controls and electronics family is engineer-only, because the fixes sit inside the casing or involve gas parts. F.61 and F.62 are a good example: the cause can be the gas valve, its wiring or the main PCB, and only testing tells you which.

One code catches people out after a home upgrade. F.49 sometimes shows up after new thermostats or controls are wired in. It relates to the boiler's eBUS control connection, so the controls wiring is the first suspect. That's a job for whoever fitted the controls or a heating engineer.

Found your code? Jump to the matching section below. If it's engineer-only, skip ahead to the advice on booking a Gas Safe engineer.

F.22 and Low Pressure: Why the Same Code Can Mean Different Problems

F.22 means the boiler thinks there isn't enough water pressure to run safely. It's a form of dry fire protection, so the boiler won't fire without enough water inside. Usually a top-up through the filling loop sorts it. If it keeps coming back, the real question is where the water is going.

This is the clearest example of one code with several causes. Behind an F.22 you might find:

• a one-off drop after bleeding radiators
• a slow leak on a radiator valve or pipe
• a dripping pressure relief valve
• a flat expansion vessel
• a faulty pressure sensor

Each one needs a different fix. Topping up again and again only delays the real repair.

How to Top Up Your ecoTEC Pressure

Most systems sit at roughly 1 to 1.5 bar when cold. Your model's manual gives the exact figure, so check it first.

1. Turn the heating off and let the system cool.
2. Find the filling loop. Many ecoTEC plus combis have a built-in loop under the boiler. System boilers often use an external braided hose.
3. Open the valve slowly while you watch the gauge.
4. Stop at around 1 to 1.5 bar, then close the valves fully.
5. Reset the boiler once.

Don't overfill. Pressure relief valves usually open at about 3 bar, so too much water can end up discharging outside through the small pipe on your wall. Never leave the loop open. If you have an external hose, disconnect it after use, as water regulations require.

If the Pressure Keeps Dropping

A single drop after bleeding radiators is normal. Needing to top up regularly means the system is losing water somewhere. Work through these checks:

• Radiators and pipework: look for drips or damp patches around valves and visible pipes.
• The small copper pipe outside: drips or a wet wall below it suggest the pressure relief valve is letting water out.
• High when hot, low when cold: if the gauge climbs a lot with the heating on and sinks when it's off, the expansion vessel is often the cause.
• No visible leak: hidden leaks under floorboards are common in older London terraces and conversions.

Relief valve and expansion vessel work is an engineer job. So is tracing a leak you can't see.

When the Gauge Looks Fine but F.22 Won't Clear

If the gauge reads normally and the code stays, the boiler may be getting a false reading. The pressure sensor, its wiring, or an air-locked or seized pump can all cause this. Don't keep adding water to chase the code. You'll overfill the system and could end up with a relief valve discharge on top. Book a Gas Safe engineer instead.

Vaillant F28 Fault: Why Won't Your Boiler Light?

F.28 means the boiler tried to light at start-up and couldn't. F.29 means it lit, lost the flame and failed to relight. Both often come down to the gas supply or a blocked or frozen condensate pipe before any part is at fault.

Once the simple causes are ruled out, an engineer looks at:

• the ignition or flame-sensing electrode
• the gas valve
• low gas pressure
• flue problems
• the main PCB

That's five different fixes behind one code, which is why proper diagnosis matters more than a quick part swap.

Quick Checks Before You Call

• Try the hob or another gas appliance. If it works, gas is reaching your home.
• Check the gas meter valve. When the handle on the emergency control valve is in line with the pipe, it's on.
• Check your prepayment credit. Prepayment meters are common in rented flats. Running out of credit cuts the gas, which triggers an ignition lockout.
• In freezing weather, check the condensate pipe. This is the pipe that carries water from the boiler to a drain outside. If it's frozen, thaw it with warm water, never boiling water.
• Then reset the boiler once.

Frozen condensate pipes are a classic cause of ignition and flame lockouts in a cold snap. Industry guidance recommends external condensate runs of at least 32mm, insulated. Our winter plumbing checklist for London covers frost prep for the rest of your pipework too.

When It's Time for an Engineer

Call a Gas Safe engineer if:

• F.28 or F.29 comes back after one reset
• the gas supply is fine and there's no frost
• you notice a smell, an unusual noise or soot

Never touch the gas valve or electrodes, and don't keep resetting an ignition lockout.

If none of the gas appliances in your home work, the problem may be the gas supply itself. Call the National Gas Emergency Service on 0800 111 999.

Vaillant F75 Fault: Pump, Air or Sludge?

F.75 means the boiler didn't see the pressure change it expected when the pump started. Many people assume the pump has died. Air, low pressure or sludge around the pressure sensor are just as likely.

Here's what's going on. When the pump kicks in, the water pressure should rise a little. The pressure sensor watches for that rise. If air, sludge or a faulty sensor hides it, the boiler logs F.75. The pump itself may be working perfectly well.

Try these steps first:

1. Check the gauge and top up if the pressure is low.
2. With the heating off and cool, bleed the radiators.
3. Check the pressure again, since bleeding lets some out, and top up if needed.
4. Reset the boiler once.

If F.75 comes back, it's time for an engineer. When we're called to an F.75, we check the sensor, pump and water quality before replacing anything. Depending on what we find, the fix could be:

• cleaning or replacing the pressure sensor
• fitting a magnetic filter to catch sludge
• a chemical system clean or a powerflush for heavily sludged systems
• adding inhibitor to the system water

F.20, F.23 and F.24 often share the same root causes as F.75. All four can come from poor circulation caused by air, sludge or a partly closed valve. If you've had more than one of these codes, the system water is the likely link between them.

Sludge is common in older radiator circuits across London. It's especially common in period homes where a new combi was fitted onto old pipework. The boiler is new, but the water running through it may carry years of debris.

Should You Reset It Yourself or Call a Gas Safe Engineer?

You can safely check pressure, top up, bleed radiators, thaw a condensate pipe, check the gas supply and controls, and press reset once. Anything inside the casing, anything involving gas parts, or any code that returns after one reset is a job for a Gas Safe engineer.

The one-reset rule is simple. Reset once, after you've fixed the likely cause. If the code comes back, stop. Repeated resets hide a real fault. On ignition and flame codes like F.28 and F.29, forcing the boiler to try again and again isn't safe.

If your Vaillant is still under guarantee, check the terms before booking anyone. Warranties usually need a record of annual servicing. Vaillant's customer service team is on 0330 100 3143 for warranty repairs.

Whoever you book, check their Gas Safe ID card and make sure they're qualified for domestic gas boilers. You can verify an engineer online with the Gas Safe Register or by calling 0800 408 5500.

Booking a Vaillant Boiler Repair in London

A few details make your visit quicker and cheaper:

• Share your photo of the code, the pressure reading and when the fault happens.
• Ask for the diagnostic or callout fee upfront.
• Ask whether the engineer carries common Vaillant parts, so you're more likely to get a first-visit fix.
• If there's no heat or hot water and someone vulnerable lives with you, say so when you book, so the visit can be prioritised.

Our Vaillant boiler repair service covers homes across Greater London, with Gas Safe engineers who work on the ecoTEC range.

We don't list prices here because the cost depends on what's really behind the code. Ask InstaGasWorks for a quote and we'll talk you through the costs before we book the visit.

If You're a Landlord

The Gas Safety (Installation and Use) Regulations 1998 require an annual gas safety check by a Gas Safe registered engineer. Tenants must get a copy of the record within 28 days, and you must keep records for 2 years. Under the Landlord and Tenant Act 1985, you must also keep heating and hot water installations in repair and working order.

When a tenant reports a code:

• Ask for a photo of the display and the pressure reading.
• Only ask tenants to do simple checks, like topping up the pressure. Never ask them to open or adjust the boiler.
• Keep a log of codes and repairs alongside your gas safety records.

A one-page note by the boiler saves a lot of back and forth. Here's a simple version you can adapt:

Boiler help note Boiler: Vaillant ecoTEC [model]. Normal pressure when cold: [figure from manual] bar. Showing F.22? Top up using the filling loop to [figure] bar, close the valves fully and press reset once. Any other code, or F.22 back again? Take a photo of the display and send it to your landlord or letting agent straight away. Smell gas? Leave the property and call 0800 111 999.

Keeping Your Vaillant Running Smoothly This Winter

Most of these codes are preventable. An annual service, clean system water and a bit of prep before the first frost go a long way.

It's late September, so now's the time to get ready:

• Check your pressure while the system is cold, and top up if it's low.
• Put the heating on and bleed any radiators that are cold at the top.
• Make sure external condensate pipes are insulated.
• Book your annual boiler service. It's usually a condition of Vaillant's manufacturer warranty as well.
• At the service, ask whether a magnetic filter and inhibitor are fitted and topped up.

Cold-weather lockouts from frozen condensate pipes are one of the most common winter callouts. Insulating the pipe now is a small job compared with a no-heat morning in January.

Keep a note of any codes and when they appear. Patterns help an engineer find the real cause faster. An F.22 that returns every few weeks points somewhere very different from one that appeared once after bleeding radiators. A simple log works well:

When Vaillant Boiler Fault Codes Keep Coming Back

If a code has come back after one reset, that's your cue to stop trying and book a Gas Safe engineer. Our team works on Vaillant ecoTEC boilers across Greater London, from F.22 pressure problems to ignition faults, with 24/7 support for urgent no-heat situations. Send us a photo of your display and book a visit, and we'll take it from there.