F23 Vaillant fault code meaning, causes and fixes
Vaillant F23 errors are applicable to Vaillant Ecotec Pro, Ecotec Plus, and Ecotec Exclusive.
Vaillant F23 is an error code that’s caused by large temperature differences between flow and return pipes. This can be caused by many possible causes and should be addressed by a professional Gas Safe registered heating engineer.
Get new boiler quotes online >
It is not a fatal mistake for boilers and a part may just need to be replaced to get your central heating system and hot water back up and running in no time so no need to worry about the dreaded new boiler cost just yet.
Old inefficient boiler costing you money? Read our guide to Vaillant boiler prices here for more information.
What does the Vaillant F23 Error mean?
The Vaillant F23 fault code refers to the difference between flow and return pipes.
The boiler heats water through the flow pipe. The water returning to the boiler after it has been around the central heating system enters the boiler through the return pipe.
The temperature between the pipes will always be different but you need to ensure accurate temperature monitoring for safety.
The flow pipe will be warmer because it is the one that directs hot water into the heating system from the primary heat exchanger.
The boiler heats up faster than the pipes and radiators as this is where the heat exchanger is and everything starts. This is because the water doesn’t cool as much as it travels around the heating system and the temperature difference between return and flow pipes only decreases slightly.
Vaillant F23 errors occur when the temperature difference between two pipes is out of range. If the difference exceeds 35 degrees, you will see an F23 error code. This code triggers a safety switch off.
What Causes an F23 Vaillant Error?
Multiple causes of Vaillant boiler F23 fault code can occur.
A faulty pump is one reason for an F23 error on a Vaillant boiler. Your boiler is heating water but the pump isn’t moving it around fast enough. This means that water will have cooled significantly by the time it reaches its return pipe, as it is cooler than it should before entering pipes or radiators.
There are many possible causes for a faulty pump, some of which can be easier to fix than others.
It is possible that the speed setting was incorrect. If it is set too low then water will not move as fast and will lose temperature. There could also be a build up of central heating sludge which affects how the pump works.
An air lock is another common reason for the F23 error. An air lock can be found anywhere in the heating system, from the boiler pump to bathroom towel rail.
You can avoid air locks in towel rails and radiators by regularly bleeding them. An airlock in the boiler pump is easy to identify as the boiler will make a clicking or banging sound.
A physical blockage, such as the rust in pipes and radiators, or limescale buildup can also cause an F23 error.
This decreases the pipe’s capacity, which causes water to flow more slowly through the pipes and increases the temperature difference between the return and flow pipes.
You may also be at fault with your thermostat. This simply means that the boiler is not functioning correctly due to improper temperature regulation.
How to fix a Vaillant F23 Error
Depending on the problem, it may be more difficult or easier to correct a pump fault. The flow setting should be adjusted if it is too low.
If you suspect that the problem is caused by a stuck shaft, or any other defective components, it is best to replace the entire pump. These errors are very likely to occur again.
A thermistor fault can be solved the same way, since the element will likely degrade further after it malfunctions.
If the error code is caused by an airlock, it’s easiest to fix. The boiler pump and radiators must be flushed to release trapped air.
To reduce the chance of another blockage, hot flushing with chemicals may be necessary if there is a physical obstruction and to remove central heating sludge.
How can you fix a Vaillant F23 error yourself?
The Vaillant F23 fault code can be caused many ways so it is best that you call an experienced plumber to diagnose the problem and then fix it.
You can eliminate the possibility of the problem being down to airlocks. If an F23 error code appears, be sure to flush all radiators and towel rails.
Bleaching an airlock in the boiler pump is a task that requires the removal of the boiler’s front. This should be done only by a Gas Safe registered engineer.
If the error is caused by something other than physical blockage, chemical flushing may be required. This cannot be done by a layperson.
These cases are why it is important to invest in a boiler filter or limescale reducer.
They should be cleaned at each service to significantly reduce the chance of an F23 error happening again.
If the Vaillant boiler F23 fault code is caused by a defective pump or thermistor. This can only be fixed by replacing the defective component. Professionals should also do this.
Getting an annual boiler service can help you spot and prevent these fault codes appearing, or other problems like the vaillant boiler egg timer as professional Gas Safe engineers are professionally trained to find these types of problems.
What Does it Cost to Fix a Vaillant F23 fault code?
There may be a charge for calling out depending on which company you choose. While some companies will provide a free quote, others will charge for calling out. You can expect to be called out and a diagnosis within the range of £50-£70.
Repairs can cost from as low as £100, depending on what is needed. The problem could be the pump, a blockage in the system, or a defective sensor.
Does the F23 fault code mean my Vaillant boiler is broken?
An F23 error is not fatal for a boiler and can be fixed by professionals. However, if it occurs often, your boiler’s pump and thermistor may need to be replaced.
Is the boiler safe to use if it has an f23 error code?
A F23 error code will cause a safety switch-off. This means that the boiler can’t be used until it is fixed.
What do I need to do to reset my Vaillant boiler following an F23?
The Vaillant boiler can be reset after it displays an error code. However, if the boiler is not fixed immediately, the boiler will display the error code again and lockout. To restart your boiler, make sure you have addressed the problem.
Is the F23 the same as the Boiler Overheating?
Boiler overheating can cause problems similar to the F23 error. However, they are not the exact same thing. You are more likely than not to see F20 if your boiler is heating too much.
Does the F23 fault code mean I need a new boiler?
We have access to the most qualified boiler repair professionals available and you can get a fixed price quote on a full new Vaillant boiler installation online now. If you have an old boiler that is over 10 years old then it will have become less energy efficient but the F23 fault could be the start of more fault codes occurring which will no doubt mean more high repair costs.
