Vaillant boiler fault codes: what each one means
A Vaillant boiler shows a fault on its display as F and a number: three digits on the current ecoTEC plus (F.022), two on the ecoFIT pure and ecoTEC exclusive (F.22). The tables below give each common code's meaning and what Vaillant says to do or check, from its own installation manuals.
Reviewed by Jordan Valentine-Dunn, Gas Safe registered engineer · Portsmouth Gas Heating · Last reviewed September 2026
Most calls start with water pressure. Every current Vaillant range warns with a flashing pressure value before it shuts down, and the shutdown point differs by range, so read the gauge before treating F.22 as a failed part.
When does each Vaillant range lock out on low pressure?
| Range | Pressure value flashes below | Shuts down with the fault at | Reset, in Vaillant's words |
|---|---|---|---|
| ecoTEC plus (current VU/VUW) | 0.8 bar | 0.3 bar or less, showing F.022 | Hold the reset button for longer than three seconds. Maximum number of repetitions: 3. |
| ecoFIT pure combi and system | 0.5 bar | Below 0.3 bar; the display shows 0.0 bar and F.22 is stored in the fault list | Press reset (max. three times) to restart the product. |
| ecoTEC exclusive 835 and 843 | 0.8 bar | Below 0.5 bar, showing F.22 | Press reset (max. three times) to restart the product. |
Vaillant gives the operating fill pressure as 1.0 to 2.0 bar on the ecoTEC plus and exclusive and 1.0 to 1.5 bar on the ecoFIT pure. On every range it says that if the fault recurs despite reset attempts, contact customer service.
What do the ecoTEC plus fault codes mean?
| Code | Meaning (Vaillant's words) | Manufacturer's stated action |
|---|---|---|
| F.022 | No/insufficient water in the product or the water pressure is too low. | Fill the heating installation and check the product and system for leaks; check the water pressure sensor, its wiring, the pump cable, the automatic filling device and the internal expansion vessel. |
| F.028 | The flame signal was not detected during the ignition phase. | Open the gas isolator cock; check gas connection and flow pressure; reset once for air in the gas supply; check the condensate discharge and siphon, the flue gas route, electrodes and earthing. |
| F.029 | The ignition following a flame loss during operation was unsuccessful. | Check the gas supply, the flue gas route, earthing, the air intake pipe, the condensate discharge including the siphon, and the electrodes. |
| F.020 | The safety cut-out (SCO) interrupts the gas valve control. | Fill the installation and check for leaks; check the flow and return sensors and wiring, the pump, the 3-port diverter valve and the water pressure sensor. |
| F.075 | The pressure change is too low when the heating pump is started up. | Check the system pressure, fill and purge; check the water pressure sensor, the pump and the internal expansion vessel. |
| F.347 | Condensate has been detected in the combustion chamber. The burner operation is interrupted. | Check and clean the condensate discharge pipe including the siphon; check the combustion chamber. |
What do the ecoFIT pure fault codes mean?
| Code | Meaning (Vaillant's words) | Possible cause (Vaillant's words) |
|---|---|---|
| F.22 | Safety shutdown: Water deficiency in the boiler | No or insufficient water in the product, water pressure sensor defective, cable to the pump or to the water pressure sensor loose, not connected or defective. |
| F.28 | Fault: Ignition unsuccessful when starting up | Includes gas pressure switch triggered, air in gas, gas flow pressure too low, ignition system or ionisation fault, incorrect earthing, condensate siphon blocked. |
| F.29 | Fault: Flame loss | Gas supply temporarily stopped, flue gas recirculation, incorrect earthing of product, ignition transformer has spark failure, condensate siphon blocked. |
| F.20 | Safety shutdown: Overheating temperature reached | Incorrect earth connection, flow or return NTC defective (loose connection), stray spark via ignition cable, ignition plug or ignition electrode. |
| F.75 | Fault: Pressure sensor | Pressure switch defective. |
| F.83 | Fault: Dry fire | Insufficient water in the product, or the flow or return temperature sensor is not in the correct position on the pipe. |
What do the ecoTEC exclusive fault codes mean?
| Code | Meaning (Vaillant's words) | Possible cause (Vaillant's words) |
|---|---|---|
| F.22 | Safety switch-off: Low water pressure | No or insufficient water in the product, water pressure sensor defective, cable to pump or water pressure sensor loose, not connected or defective. |
| F.28 | Start-up failure: Ignit. unsuccessful | Includes gas flow monitor triggered, air in gas, gas flow pressure too low, condensate route blocked, ignition system or ionisation fault, incorrect earthing. |
| F.29 | Operating failure: Ignit. unsuccessful | Gas supply temporarily stopped, flue gas recirculation, condensate route blocked, defective earthing of product, ignition transformer has spark failure. |
| F.35 | Fault: Air/flue gas duct | Check the entire air/flue pipe for permitted design, restriction or blockage, and damage; then reset the product. |
| F.56 | Safety switch-off: CO limit exceeded | A component in the combustion regulation is defective; if the fault occurs again after being reset, the gas valve assembly is defective. |
| F.75 | Fault: Pump/ water shortage | Water pressure sensor and/or pump defective, air in the heating installation, insufficient water in the product. |
The same number can mean different things by range: F.75 is a pressure sensor fault on the ecoFIT pure, a pump or water shortage fault on the exclusive, and too little pressure change at pump start on the ecoTEC plus. Read the table for the range on the data plate. The ecoFIT pure and exclusive manuals list causes rather than a step per cause.
How do you read a code on the job? Two examples
An ecoTEC exclusive shows a flashing 0.6 bar and no F code. It is below the 0.8 bar warning point but above the 0.5 bar shutdown, so it is still running. Vaillant says to top up; the value keeps flashing until the pressure reaches 1.1 bar.
An ecoTEC plus shows F.028 on a frosty morning. Vaillant warns that F.028, F.029 and F.347 appear after a delay, and that if a frozen condensate pipe caused them, thawing the pipe is not sufficient: the condensate siphon must be serviced.
When should you stop resetting and call an engineer?
After the third reset. Vaillant limits resets to three on all three ranges and says to contact customer service if the fault recurs. On the exclusive, F.56 is a CO limit shutdown, and Vaillant's note is that if it occurs again after a reset, the gas valve assembly is defective.
A fault code is the manufacturer's diagnostic starting point, not a repair. Only a Gas Safe registered engineer may open the appliance: regulation 3 of the Gas Safety (Installation and Use) Regulations 1998 limits gas work to an HSE-approved class of persons. If you smell gas, reset nothing and call the National Gas Emergency Service on 0800 111 999.
For engineers, Manifold's fault codes library records every code seen on your team's checks against the appliance, so a repeat visit starts with last time's fault, and its manuals lookup finds Vaillant's documentation by GC number.
Read next
Frequently asked
Sources
- Vaillant, ecoTEC plus installation and maintenance instructions (0020308118_06)
- Vaillant, ecoFIT pure 825 to 835 installation and maintenance instructions (0020230531_07)
- Vaillant, ecoFIT pure 612 to 630 installation and maintenance instructions (0020230533_07)
- Vaillant, ecoTEC exclusive 835 and 843 installation and maintenance instructions (0020193968_05)
- Legislation.gov.uk, Gas Safety (Installation and Use) Regulations 1998, regulation 3
- National Gas, emergency contacts
Related guides
Last reviewed September 2026. This guide is general information, not legal or safety advice, gas safety work must be carried out by an appropriately Gas Safe registered engineer. Rules can change, so check the linked official sources for the current position.