Common Vaillant boiler faults

The most common Vaillant fault codes

Common Vaillant Boiler faults

In this guide, we are going to highlight the most common Vaillant boiler faults that can show up on your boiler and explain what they mean so you can solve any issues yourself at home.

 

Things to Consider if you have a Vaillant boiler faults:

Before you begin to stress and worry about being out of pocket when a code appears on your Vaillant boiler faults, there are three things you should consider first:

Is Your Boiler Still Covered?

Vaillant is renowned for having long warranties on their boilers, so the first thing to do whenever an issue arises is to check whether you are still covered.

In some cases, your boiler might be backed by a ten-year warranty which can make it cheaper to have any issues resolved by a professional.

Check your warranty length using Worcester Bosch online guarantee checker

Have You Reset The Boiler?

We have all heard the classic ‘turn it off and on again’ as a solution for when things go wrong, but there is some truth behind the cliché.

In some cases, an error code might show even if there is not a mechanical problem so to save yourself time and effort try turning the device off to see whether it goes away.

If the error code appears once the boiler has rebooted, it is time to look further into it.

Any worcester Boiler installed since 2019 will have the error name rather then an error code.

Have you checked the pressure?

Low pressure is a sign that there isnt enough water in your system, Check for leaks and top up using the filling loop. This can be located on your boiler or externally underneath your boiler. Occasionally it is located else where around the house. Consult your installation instructions on advice on how to do this.

F.22 Vaillant faults codes

Error Description
Safety switch-off: low water pressure. Shown on display as F.22

Error Cause
No pressure or water pressure too low in the boiler, water pressure sensor defective, cable to pump or water pressure sensor loose/not connected/defective

Fix Vaillant F.22 Error Code

  1. Top up the pressure of the boiler or system using the internal filling loop if it is a combi boiler, otherwise using the external filling loop attached to the system. View the WarmZilla guide to repressurise your boiler.
  2. The pressure sensor connection may have come out or become loose. Take the cable out, check it’s not broken and re-insert.
  3. Check that the pump connection is not loose. If necessary, remove the connection from the connector, check and re-insert.

Vaillant F.23 Vaillant fault codes

Error Description
Safety switch-off: Temperature difference too great

Error Cause

  • Inadequate Pump Operation
  • Blockage Or Air Lock Within The Appliance (No Water Movement)
  • Blockage Or Air Lock In The Heating System (No Water Movement)
  • Check Domestic Hot Water Heat Exchanger and Domestic Hot Water Heat Exchanger Filter For Debris If Fault Occurs On Hot Water Mode Only
  • Check Resistance On The Heating Flow & Return NTC Thermistors To Ensure Accurate Temperature Monitoring (Should Read 12K ohms @ 20C

Fix Vaillant F.23 Error Code
Check the Flow and return NTC sensors. Check the wiring using a continuity tester and resistance tester if necessary. Replace NTC, harness or PCB as necessary dependent on checks.

Make sure there are no blockages in the pipework.  If there is debris in the system, flushing may be required. Then individual components may require cleaning or replacing dependent on damage caused by debris.  You may need to activate the pump purge program (see P Codes). Also check the domestic heat exchanger is free of debris, cleaning the filter as necessary.

Vaillant F.24 Vaillant fault codes

Error Description
This vaillant boiler fault according to Vaillant Instructions and Servicing manual is Water Circulation Fault (Temperature Rise Greater Than 10 Degrees Celcius Per Second)

Error Cause

  • Inadequate Pump Operation
  • Isolation Valves Closed Under The Appliance
  • Blockage Or Air Lock Within The Appliance (No Water Movement)
  • Blockage Or Air Lock In The Heating System (No Water Movement)
  • Check Domestic Hot Water Heat Exchanger and Domestic Hot Water Heat Exchanger Filter For Debris If Fault Occurs On Hot Water Mode Only
  • Check Resistance On The Heating Flow & Return NTC Thermistors To Ensure Accurate Temperature Monitoring (Should Read 12K ohms @ 20C

Fix Vaillant F.24 Error Code
Check the isolation valves are open under the boiler.

Check the Flow and return NTC sensors. Check the wiring using a continuity tester and resistance tester if necessary. Replace NTC, harness or PCB as necessary dependent on checks.

Make sure there are no blockages in the pipework.  If there is debris in the system, flushing may be required. Then individual components may require cleaning or replacing dependent on damage caused by debris.  You may need to activate the pump purge program (see P Codes). Also check the domestic heat exchanger is free of debris, cleaning the filter as necessary

Vaillant F.28 Vaillant fault codes

Error Description
Failure during start-up: ignition unsuccessful.

Error Cause

  • Gas meter defective or gas pressure regulator has triggered,
  • Air in gas
  • Gas flow pressure too low
  • Thermal isolator device (TAE) has triggered
  • Condensate duct blocked
  • Incorrect gas restrictor
  • Incorrect ET gas valve
  • Fault on the gas valve
  • Multiple plug on PCB incorrectly plugged in
  • Break in cable harness
  • Ignition system (ignition transformer, ignition cable, ignition plug, ignition electrode) defective

Fix Vaillant F.28 Error Code
There are a range of issues that can cause an F.28 error code to occur, if you encounter this issue – first check to ensure gas is coming into your property. If it is then call a Gas Safe engineer to test your system and isolate the fault.

Vaillant F.29 Vaillant fault codes

Error Description
Failure during operation: Re-ignition unsuccessful

Error Cause
Gas supply temporarily stopped, flue gas recirculation, condensate duct blocked, defective earthing of product, ignition transformer has spark failure.

Fix Vaillant F.29 Error Code
Check the gas supply into the property. If gas is coming into property then call a Gas Safe engineer to identify the issue. If gas isn’t coming into the property check with your gas provider.

Vaillant F.54 Vaillant fault codes

Error Description
This fault code suggests there is a fault in the gas supply. Usually this fault is accompanied by an F.28 or F.29 Fault code.

Error Cause
According to Vaillant, there is insufficient gas supply to operate the unit. Gas isolator may be closed on the boiler or elsewhere. Also gas flow pressure may be too low.

Fix Vaillant F.54 Error Code
Check if the gas stop cock is fully open at the meter, near the boiler or anywhere else there may be any additional stop cocks.

Check valve is working as it should. Solenoid testing equipment and multimeters may be required. If found faulty, a replacement gas valve would be required.

Vaillant F.75 Boiler Fault Code

Error Description
No pressure change detection when starting-pump.

Error Cause
The number one cause of this vaillant boiler fault is some sort of blockage or has caused a component to fail. When diagnosing which component has failed, you need to check for the presence of sludge. If there is sludge, this should be cleaned out or system powerflushed before changing components.

Fix Vaillant F.75 Error Code
A gas engineer will need to check the system to identify whether there is a blockage in your boiler or system. A powerflush may be required if a blockage is identified. Checking pump seals and pump is another fix for this error.

Vaillant boiler faults F.77

Error Description
Flue non-return flap/condensate pump fault

Error Cause
Blockage to condensate pump or malfunction of condensate pump

Fix Vaillant F.77 Error Code
A gas engineer will need to check the condensate pump for a blockage and clear if there is one. In the case of no blockage, a new condensate pump will be required.

Vaillant boiler faults F.22 

Error Description
Safety switch-off: low water pressure. Shown on display as F.22

Error Cause
No pressure or water pressure too low in the boiler, water pressure sensor defective, cable to pump or water pressure sensor loose/not connected/defective.

Fix Vaillant F.22 Error Code

  1. Top up the pressure of the boiler or system using the internal filling loop if it is a combi boiler, otherwise using the external filling loop attached to the system. View the WarmZilla guide to repressurise your boiler.
  2. The pressure sensor connection may have come out or become loose. Take the cable out, check it’s not broken and re-insert.
  3. Check that the pump connection is not loose. If necessary, remove the connection from the connector, check and re-insert.

Vaillant boiler fault F.24 

Error Description
This vaillant boiler fault according to Vaillant Instructions and Servicing manual is Water Circulation Fault (Temperature Rise Greater Than 10 Degrees Celcius Per Second)

Error Cause

  • Inadequate Pump Operation
  • Isolation Valves Closed Under The Appliance
  • Blockage Or Air Lock Within The Appliance (No Water Movement)
  • Blockage Or Air Lock In The Heating System (No Water Movement)
  • Check Domestic Hot Water Heat Exchanger and Domestic Hot Water Heat Exchanger Filter For Debris If Fault Occurs On Hot Water Mode Only
  • Check Resistance On The Heating Flow & Return NTC Thermistors To Ensure Accurate Temperature Monitoring (Should Read 12K ohms @ 20C

Fix Vaillant F.24 Fault code
Check the isolation valves are open under the boiler.

Check the Flow and return NTC sensors. Check the wiring using a continuity tester and resistance tester if necessary. Replace NTC, harness or PCB as necessary dependent on checks.

Make sure there are no blockages in the pipework.  If there is debris in the system, flushing may be required. Then individual components may require cleaning or replacing dependent on damage caused by debris.  You may need to activate the pump purge program (see P Codes). Also check the domestic heat exchanger is free of debris, cleaning the filter as necessary.

Vaillant F.28 Boiler Fault Code

Error Description
Failure during start-up: ignition unsuccessful.

Error Cause

  • Gas meter defective or gas pressure regulator has triggered,
  • Air in gas
  • Gas flow pressure too low
  • Thermal isolator device (TAE) has triggered
  • Condensate duct blocked
  • Incorrect gas restrictor
  • Incorrect ET gas valve
  • Fault on the gas valve
  • Multiple plug on PCB incorrectly plugged in
  • Break in cable harness
  • Ignition system (ignition transformer, ignition cable, ignition plug, ignition electrode) defective

Fix Vaillant F.28 Error Code
There are a range of issues that can cause an F.28 error code to occur, if you encounter this issue – first check to ensure gas is coming into your property. If it is then call a Gas Safe engineer to test your system and isolate the fault.

Vaillant F.29 Boiler Fault Code

Error Description
Failure during operation: Re-ignition unsuccessful

Error Cause
Gas supply temporarily stopped, flue gas recirculation, condensate duct blocked, defective earthing of product, ignition transformer has spark failure.

Fix Vaillant F.29 Error Code
Check the gas supply into the property. If gas is coming into property then call a Gas Safe engineer to identify the issue. If gas isn’t coming into the property check with your gas provider.

Vaillant F.67 Boiler Fault Code

Error Description
Flame Signal Fault On The Main PCB

Error Cause

  • Damaged Or Loose Electrical Connection On The Main PCB
  • Main PCB Fault
  • Mains Input Voltage Problem (Reverse Polarity, Poor Earth Etc)

Fix Vaillant F.67 Error Code
You will need a Gas Safe engineer to test your electronics and diagnose what part of the boiler electronics is generating the fault code.

Vaillant F.22 Boiler Fault Code

Error Description
Safety switch-off: low water pressure. Shown on display as F.22

Error Cause
No pressure or water pressure too low in the boiler, water pressure sensor defective, cable to pump or water pressure sensor loose/not connected/defective.

Fix Vaillant F.22 Error Code

  1. Top up the pressure of the boiler or system using the internal filling loop if it is a combi boiler, otherwise using the external filling loop attached to the system. View the WarmZilla guide to repressurise your boiler.
  2. The pressure sensor connection may have come out or become loose. Take the cable out, check it’s not broken and re-insert.
  3. Check that the pump connection is not loose. If necessary, remove the connection from the connector, check and re-insert.

Vaillant F.24 Boiler Fault Code

Error Description
This fault according to Vaillant Instructions and Servicing manual is Water Circulation Fault (Temperature Rise Greater Than 10 Degrees Celcius Per Second)

Error Cause

  • Inadequate Pump Operation
  • Isolation Valves Closed Under The Appliance
  • Blockage Or Air Lock Within The Appliance (No Water Movement)
  • Blockage Or Air Lock In The Heating System (No Water Movement)
  • Check Domestic Hot Water Heat Exchanger and Domestic Hot Water Heat Exchanger Filter For Debris If Fault Occurs On Hot Water Mode Only
  • Check Resistance On The Heating Flow & Return NTC Thermistors To Ensure Accurate Temperature Monitoring (Should Read 12K ohms @ 20C

Fix Vaillant F.24 Error Code
Check the isolation valves are open under the boiler.

Make sure there are no blockages in the pipework.  If there is debris in the system, flushing may be required. Then individual components may require cleaning or replacing dependent on damage caused by debris.  You may need to activate the pump purge program (see P Codes). Also check the domestic heat exchanger is free of debris, cleaning the filter as necessary.

Vaillant F.63 Boiler Fault Code

Error Description
If you have a F63 fault code displayed on your Vaillant boiler, there is a problem with the circuit board (PCB). The PCB is what communicates with all electronic components.

Error Cause

  • Old age; general wear and tear
  • Connections to and from the PCB have worked loose, or have been damaged
  • The PCB has not been setup correctly by a service engineer after a service, new boiler, or new PCB installation

Fix Vaillant F.63 Error Code
Usually this will require a new PCB which can cost between £350-£450. You may want to consider replacing your boiler if it is getting on in years.

Vaillant F.67 vaillant boiler faults

Error Description
Flame Signal Fault On The Main PCB

Error Cause

  • Damaged Or Loose Electrical Connection On The Main PCB
  • Main PCB Fault
  • Mains Input Voltage Problem (Reverse Polarity, Poor Earth Etc)

Vaillant F.22 Boiler Error Code

Error Description
Safety switch-off: low water pressure. Shown on display as F.22

Error Cause
No pressure or water pressure too low in the boiler, water pressure sensor defective, cable to pump or water pressure sensor loose/not connected/defective

Fix Vaillant F.22 Error Code

  1. Top up the pressure of the boiler or system using the internal filling loop if it is a combi boiler, otherwise using the external filling loop attached to the system. View the WarmZilla guide to repressurise your boiler.
  2. The pressure sensor connection may have come out or become loose. Take the cable out, check it’s not broken and re-insert.
  3. Check that the pump connection is not loose. If necessary remove the connection from the connector, check and re-insert.

Sometimes, Vaillant boiler faults indicate a small problem that can be solved at home. However, it is always a good idea to get an engineer to check your handywork.

 

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