How to Fix Vaillant Boiler Faults

Vaillant boilers are known for their reliability, but any boiler can develop a fault over time. When a fault code appears on the display, it's identifying a specific problem that needs attention.

Some issues, such as low system pressure, can often be resolved safely at home. Others involve gas or electrical components and should only be inspected by a Gas Safe registered engineer.

This guide explains the most common Vaillant boiler faults, what the fault codes mean and when it's time to arrange a repair.

Understanding Vaillant Boiler Fault Codes

Most Vaillant fault codes begin with the letter F followed by two numbers. Although different models have slight variations, many codes are shared across the ecoTEC, ecoFIT Pure, system and regular boiler ranges.

If you're looking for a full list of manufacturer error codes, see our complete guide to Vaillant boiler fault codes.

Common Vaillant Boiler Fault Codes

Below is a summary of the faults homeowners search for most often. Each links to the fuller explanation on its own dedicated page where one exists.

F13 – Cylinder Temperature Sensor Fault

F13 usually means the sensor monitoring your hot water cylinder temperature is giving an inaccurate or missing reading. Because this affects an electrical safety component, it should be inspected by a qualified Gas Safe engineer.

F22 – Low Water Pressure

F22 means the boiler has detected low or no water pressure and has shut down as a safety measure. Topping up the pressure using the filling loop often clears the fault — if it returns quickly, arrange a professional inspection.

F24 – Rapid Flow Temperature Rise

F24 means the flow temperature is climbing too quickly, usually because water isn't moving through the system properly. It's an earlier-stage warning than F25 — if F24 isn't resolved, the temperature can keep rising until the boiler trips the more severe F25 overheat shutdown.

F25 – Flue Gas Temperature Too High

F25 means the flue gas temperature has gone too high, usually because of a loose flue-gas thermostat plug, though poor circulation or a faulty sensor can also cause it. Because this affects internal components, it should be inspected by a qualified Gas Safe engineer.

F28 – Ignition Failure

F28 means the boiler attempted to ignite several times but couldn't establish a flame, so it has locked out. A single reset may clear a temporary fault, but persistent F28 faults need professional diagnosis.

F29 – Flame Loss

F29 means the burner flame went out during operation or failed to relight. Because this affects gas and combustion safety components, it should be inspected by a qualified Gas Safe engineer.

F61 – Gas Valve Fails to Open

F61 means the PCB cannot correctly open the gas valve during ignition, so the burner cannot light. Because this affects gas control components, it should be inspected by a qualified Gas Safe engineer.

F62 – Delayed Flame Switch-Off

F62 means the gas valve has failed to close, or is taking too long to close, after the burner should have switched off. Because this involves gas flowing when it shouldn't, it should be inspected by a qualified Gas Safe engineer without delay.

F75 – Pressure Sensor Fault

F75 means the boiler cannot detect the expected pressure change after the circulation pump starts, usually pointing to a faulty pump or pressure sensor. Because this affects internal components, it should be inspected by a qualified Gas Safe engineer.

Fault Codes by Vaillant Boiler Range

ecoTEC Plus & ecoTEC Pro

These ranges commonly display F22, F28, F29, F61, F62 and F75 faults, among others covered above.

ecoFIT Pure

The ecoFIT Pure range uses many of the same fault codes as the ecoTEC series. If you own an ecoFIT Pure 825, 830 or 835, you'll commonly see codes such as F22, F28, F29 and F71. Although the codes are similar, always check the manual for your exact model before attempting any troubleshooting.

System & Regular Boilers

System and regular Vaillant boilers can display many of the same fault codes as combi models, though the exact behaviour may vary depending on the cylinder and controls fitted.

Which Vaillant Boiler Faults Can You Fix Yourself?

A small number of faults, such as F22 (low pressure), can often be resolved safely at home by topping up the system or bleeding radiators. Most other fault codes involve gas, electrical or internal components and should only be diagnosed and repaired by a Gas Safe registered engineer.

Never remove the boiler casing or attempt repairs involving gas components. Aside from safety risks, doing so may invalidate the manufacturer's warranty.

Professional Vaillant Boiler Repair Costs

Repair costs vary depending on the fault, the boiler model, the parts required and whether an emergency visit is needed. A Gas Safe engineer can provide an accurate quotation once the fault has been diagnosed.

How to Prevent Future Boiler Faults

Annual servicing by a Gas Safe registered engineer helps identify worn components, pressure issues and electrical faults before they cause a breakdown. Keeping the system pressure correct, bleeding radiators when needed and fitting a magnetic filter can also reduce the risk of common faults.

Need Help With a Vaillant Boiler Fault?

Most Vaillant fault codes are designed to prevent further damage by shutting the boiler down safely. Understanding what each code means helps you decide whether you can carry out a simple check or whether professional repairs are needed.

If your boiler repeatedly displays the same fault code, loses pressure, won't ignite or keeps locking out, it's best to arrange an inspection before the problem becomes more expensive.

If your Vaillant boiler keeps displaying a fault code, won't restart or loses pressure repeatedly, don't ignore it. Our Vaillant boiler repair engineers diagnose and repair Vaillant boilers across London — book a boiler repair today and get your heating and hot water working again.

Frequently Asked Questions - (FAQs)

Start by noting the exact fault code, then check the basics such as system pressure, gas supply and whether other appliances are affected. If the fault returns after a simple reset, a Gas Safe registered engineer will need to test the relevant components to identify the cause.

You can try resetting the boiler and check whether other gas appliances are working. If the fault returns, arrange a Gas Safe engineer to inspect the ignition system and gas supply.