Vaillant Boiler F75 Fault - How to fix

Vaillant Boiler F75 Fault - How to fix

The F75 fault code on a Vaillant boiler is a common issue that usually indicates low water pressure, however it can be caused by other issues. 

When this happens, the boiler will stop working, leaving you without heating and hot water. Fortunately, fixing this problem is usually 'straightforward' and doesn't require much technical knowhow in 'most cases'. In this article, we will discuss how to fix the F75 fault on a Vaillant boiler and the costs involved.

What Causes the F75 Fault?

Basically, your boiler is showing the F75 fault code due to a sensor in the boiler not detecting adequate water flow/pressure on the start up sequence. 

If you're lucky the F75 fault is caused by a normal drop in water pressure in the heating system however, they are several other reasons why F75 might occur.

1. The most common is cause low water pressure, it can be caused by a leak in the system, which can cause the pressure to drop, this can can be caused by pressure relief valve, broken airlocks in the system or a faulty expansion vessel. However, a lot of the time, pressure in a heating system can drop by bleeding a radiator or natural pressure loss. 

2. Faulty low water pressure sensor (very common) the low water pressure sensors tend to clogg up on these and need to be replaced, quite an easy job! 

3. Defective pump - you will need to replacing your pump, as the boiler is not detecting water movement from it. 

How to Fix the F75 Fault Code?

To attempt to fix the F75 fault yourself, you will need to repressurise the heating system. 

Here's how to do it:

Step 1: Turn off the boiler and let it cool down completely.

Step 2: Locate the filling loop, which is a flexible pipe that connects the cold-water mains to the boiler. It is usually located near the boiler and may be connected to a valve or tap.

Step 3: Open the filling loop valve or tap slowly, allowing water to flow into the system. Keep an eye on the pressure gauge and stop filling when it reaches between 1 and 1.5 bar.

Step 4: Close the filling loop valve or tap and switch the boiler back on.

Step 5: Check the pressure gauge again after a few minutes to ensure that the pressure has stabilised.

Step 6: Reset boiler. 

If the pressure drops again after a short time, this indicates that there is a leak in the system. You will need to call a qualified technician to locate and fix the leak.

This does not cover the low water pressure sensor or the pump - you will need to call a boiler engineer if the above steps do not clear the F75 code. 

Costs Involved in Fixing the F75 Error Code

The cost of fixing the F75 fault on a Vaillant boiler will depend on the root cause of the problem. If it's just a matter of repressurising the system, you can do it yourself at no cost. However, if there is a major leak or another underlying issue like like the pump, you will need to call a technician for servicing.

F75 on a Vaillant boiler can be a bigger issue. 

I have had it on many ocasions where the F75 fault is triggered by a defective pump, this can be a costly problem, as the pump would need to be replaced. 

The cost of hiring a boiler engineer will depend on several factors, such as the severity of the problem, how experienced they are, time of year and how bigger company you choose. On average, you can expect to pay anywhere from £50 to £150 for a callout fee, and an hourly rate of £60 to £100. You will also be charged for any parts that need to be replaced.

As an approximate guideline: 

Repressurising your boiler - less than 1 hour, average cost £75.00 

Replacing low water pressure sensor - 90 minutes average cost, all in £150.00 

Replacing a pump - 2 hours labour - £350 all in including the pump

If your low water pressure sensor has become defective and blocked you may have sludge in your system, adding central heating inhibitor can help

Additional Things to Consider

To avoid having a possible F75 fault to deal with later, it is important to maintain your boiler regularly and have it serviced by a qualified technician at least once a year.

During a service, the technician will check the pressure, inspect the boiler for leaks, and carry out any necessary maintenance work to ensure that it is working safely and efficiently.

In conclusion, the F75 fault on a Vaillant boiler is a common issue that can usually usually be fixed by repressurising the system or replacing a low water pressure sensor. However, if there is a leak or another underlying issue, it's important to call a qualified heating technician to carry out the necessary repairs. Regular servicing of your boiler can help to prevent the F75 fault from occurring in the first place.

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