The F75 error code affects the Vaillant EcoTec models )except the ectoTec heat-only).
It signifies a problem with the pressure in the boiler, and can be caused by blockages in the pump or sensor, faulty parts which need replacing, or an incorrectly pressurised expansion vessel.
Faulty or blocked parts will need to be dealth with by a Gas Safe Engineer, but you can repressurise the boiler yourself.
What Does a Vaillant F75 Error Mean?
The F75 error code means that the boiler is detecting incorrect pressure. This means that it cannot circulate any water and therefore cannot operate. In general, the F75 points to a fault with either the pump or the pressure sensor.
What Causes a Vaillant F75 Error?
The F75 error has a couple of common causes.
Clogged Pressure Sensor
This component is prone to collecting debris and limescale, and when this gets too much it prevents the sensor from detecting pressure changes.
If the pump is faulty then this means that no water is being circulated around the system, meaning that there is no pressure for the sensor to detect.
A blocked pump, like a faulty pump, will be unable to circulate water around the heating system. Pumps usually become blocked due to a build-up of ‘heating sludge’, which is essential rust that has been picked up around the system and eventually forms a dark sludgy liquid. This substance can block pumps.
Incorrectly Pressurised Expansion Vessel
The expansion vessel is responsible for releasing excess pressure within the system, and it needs to maintain a certain pressure itself to work. If it isn’t correctly pressurised, then it can’t regulate the pressure within the boiler, resulting in an F75 error code.
On very rare occasions, the PCB is faulty and causes this problem by failing to supply power to the pump. This is not a common cause for this error code, but it is possible.
How to Fix a Vaillant F75 Error
If heating sludge blocking components has caused the issue, then your system will need either a power flush or a hot flush; neither will get rid of 100% of heating sludge as it’s an unavoidable part of the heating system, but it will resolve the F75 issue by clearing the path for water to circulate.
Fitting a scale reducer and adding a central heating inhibitor can protect against future build-ups.
If the sensor is blocked with debris and/or limescale, then it is possible to clean it – however, this is a time intensive job and it will end up costing you more in labour than it would cost to replace the part.
If the sensor is faulty rather than blocked then it will need to be replaced as it is a non-serviceable component.
Unlike the pressure sensor, a clogged pump is relatively easy to dismantle and clean so assuming it is in decent condition otherwise then there will be no need to replace the part.
If it is very worn or damaged with age, then it is worth investing in a new pump altogether.
The expansion vessel is easy to fix, as this simply needs the pressure to be topped up, which a Gas Safe Engineer will be able to do for you.
In the rare cases where the PCB is at fault, this is also a non-serviceable component that would need replacing – however, this is expensive in terms of both parts and labour and, especially if your boiler is old, it is more economical to simply get a new boiler.
Can You Fix A Vaillant F75 Error Yourself?
Whether you can fix this error yourself depends on the cause of the problem. If the issue is the pump or sensor, then an engineer will be needed to resolve the issue, whereas if the boiler simply needs repressurising you can do this yourself.
How Do I Know If the Boiler Needs Repressurising?
You will be able to see the water pressure on the indicator on the boiler’s screen – if it is too low, then the boiler will need repressurising.
Usually, if there is a problem with the pump, you will hear a rumbling noise when you reset the boiler. If the sensor is the problem, you won’t hear a rumbling noise and the pressure gauge will still be reading at the correct level.
The latter two issues will need an engineer to fix them, but if you determine that the boiler needs repressurising then you can do this yourself.
Repressurising the Boiler
Amongst the pipework beneath your boiler, you will find its filling loop; a silver flexi-pipe with one or two taps attached.
Turn the right-hand tap until it is in line with the pipework (and fully open). Then, while keeping an eye on the pressure gauge, open the left-hand tap to allow water into the boiler.
Make sure not to let the pressure get too high; it should read around 1.5. After the pressure has been balanced, make sure both taps are closed fully again to prevent the pressure rising further accidentally.
On ecoTec Plus models, the filling loop is built-in; for these, look for two small taps underneath the boiler. Open both of these until the pressure rebalances, and then close again.
Does An F75 Error Mean my Boiler is Broken?
No, an F75 is not a fatal error; it can usually be fixed by a simple parts replacement.
Is It Safe to Use the Boiler With An F75 Error Code Showing?
Yes, but it won’t work for long. The F75 is not a dangerous error – it just means that the boiler is unable to circulate water.
Will Resetting the Boiler Fix An F75?
Generally speaking, resetting a boiler does not fix a problem but just clears the error code for a short period of time – eventually, the problem will need addressing.
That said resetting a boiler that is showing an F75 error code will allow it to keep working intermittently until you can call a Gas Safe Engineer.
How Much Does Repairing an F75 Cost?
The price depends on whether the fault is caused by the pump or the sensor. If the pump needs replacing, this could cost up to £150 plus labour, and a replacement sensor could cost as much as £85 plus labour.
The parts could cost significantly less depending on the make and model required.
Could Water Damage Have Caused This Problem?
Water damage is unsurprisingly a common problem within boilers, and it is possible that the wiring and connections between the sensor, PCB and pump have been damaged by condensation.
This is quite commonly caused by leaky pump seals, and these need to be replaced as well as faulty electronics.