What does the Vaillant F75 fault code mean?
The F75 code can appear on the modern range of Vaillant Boilers, including the Ecotec Plus, Ecotec pro, EcoFit and Ecomax.
In the user manual, Vaillant defines the F75 as:
| Code | Meaning | Cause |
|---|---|---|
| F75 | Fault, no pressure change detection when starting pump | Water pressure sensor and/or pump defective, air in heating installation, too low pressure in boiler; connect external expansion vessel to return. |
This means that the boiler is experiencing a pressure issue, resulting in the boiler shutting down. This could signal 2 key causes:
- The boiler's pump is not working properly
- The sensor tasked with monitoring the water pressure is faulty
What causes the Vaillant F75 fault code?
The diagnostic process of the Vaillant F75 fault code is not quite straightforward, as the fault can often be found in combination with other related issues. So, if in doubt, it's best to contact a Gas Safe engineer. However, here are the two most common causes of the Vaillant F75 fault code that you can try to diagnose yourself.
Malfunctioning boiler pump causing the Vaillant F75 fault code
Start with checking the boiler pump. It can usually be found on the boiler return or inlet side. During normal operation, a heating pump will kick into action when a boiler fires. This usually produces a soft humming noise and it’s likely you’ll feel the boiler vibrating slightly.
If there is no noise or vibration, then the pump is probably not operational, which is the likely cause behind Vaillant F75 fault code. If your pump is seized or running slower than needed, this can also cause the Vaillant F75 fault code.
How to resolve it?
If this is the fault it will usually mean a new pump is required. If your Vaillant boiler was fitted after 2012 then this is usually just a case of removing the pump head and replacing it, which can be easily done by your engineer. However, if you have an older Vaillant Ecotec you may require the entire hydro block section that the pump head connects on to be replaced as well.
To find out which one you need, look at the pump’s data plate, which is usually screwed into the top of the pump body. If your pump’s data plate has a white background with black writing then you need both the hydro block and pump replaced. If your pump’s data plate is black with white writing, it is likely you have a newer boiler and will usually just require a new pump head installed.
Vaillant F75 caused by a faulty water pressure sensor
After you rule out potential problems with the boiler pump, another potential cause of the Vaillant F75 fault code is a blocked or partially blocked water pressure sensor. If this sensor becomes blocked then it will fail to correctly register an increase in pressure when the pump spins and will fail to ignite the boiler, causing it to lock out.
This fault can often occur in the early launch of the Vaillant EcoTec range, which ran from 2005 to 2010, due to a manufacturing fault of the water pressure sensors. If you have an older boiler, this is the likely cause of the Vaillant F75 fault code. In this case, it might make more sense to replace your boiler, as the problem is likely to persist.
How to resolve it?
If this is the cause of the Vaillant F75 fault code, then it is a good idea to arrange a boiler flush with your engineer. A Gas Safe engineer will run chemicals through the system to keep your heating water clear of sludge and dirt and prevent corrosion in your boiler and central heating system. This can either be done under normal pressure (Hot flush) or high pressure (Power flush) for more significant blockages. However, it may make more sense to replace the old water pressure sensor with a new one, as the labour costs for flushes may be higher than a replacement.
How much is it to fix a Vaillant F75 fault code?
The price depends on whether the issue is caused by the pump or the sensor. If the boiler pump needs replacing, this could cost up to £300 for a top brand like Grundfos. If you require a new boiler pressure sensor, expect to pay between £150 and £240.
How to avoid the F75 error in the future?
It is always best to practice preventive measures than to fix existing problems. Like most boiler brands, Vaillant requires their boilers to be serviced annually to remain under warranty. Even if your boiler's warranty has expired, it's important to have it serviced on a regular basis.
During the service, the Gas Safe engineer will look for any issues, run system tests and do basic maintenance, such as boiler cleaning, to prevent critical boiler parts, such as the pressure sensor, from becoming clogged.
Give your boiler a service.
Make sure you don't invalidate your warranty. Call Smart Plan to get a boiler checkup to see if everything is in good working order.
To prevent further buildup, consider purchasing a system filter. Vaillant offers them as a part of their boiler protection kits. You can buy one here.
