The following page contains information relating to the Vaillant ecoTEC F.75 fault code, including what the F.75 fault code means, its potential causes, how this fault can be potentially fixed and if your boiler is worth repairing.
The F75 fault code explained
The F75 fault code as explained in the the Vaillant ecoTEC manufacturers instructions states;
No pressure rise was detected on turning on the pump – Water pressure sensor or/and pump defective, too little water in appliance; check adjustable by-pass; connect external expansion vessel to return
So your Vaillant boiler wants to make sure that the pump is working sufficiently before it fires up to provide heating or hot water.
The boiler has a safety mechanism which can tell if the pump is running before the boiler fires up. This safety mechanism is called the “pressure sensor”.
The pressure sensor looks for a little rise in pressure inside the boiler when the pump runs.
The rise in pressure is essentially translated into a change of voltage inside the sensor which the boiler printed circuit board can interpret.
If the printed circuit board gets the right signal back from the sensor the it assumes that the pump is running and continues on with the next part of the ignition sequence.
So what causes F75 fault code?
The F.75 fault code can generally be attributed to one of two components – a faulty or blocked pressure sensor, a faulty pump – and sometimes a combination of the two.
Sometimes an issue with the expansion vessel can indirectly cause this fault or excess pressure in the system for whatever reason.
A fault with the expansion vessel can cause the pressure to spike when you put the heating on which will create too much pressure in the system and potentially cause this problem.
There are other parts that can fail which can cause this fault as well but these are generally much less common than the pump or sensor.
A faulty printed circuit board can cause this issue and on the occasions where I have seen a fault PCB being at fault, it’s been a relay failure on the board which stops putting power onto the pump.
This causes the pump not to run which in turn causes the pressure sensor not to detect a rise in pressure which in turn leads the PCB to think the pump is not working.
On a rare occasion a faulty wiring harness could potentially cause this issue but like the PCB this is not very common at all.
How to fix F75 fault code
Unfortunately the F75 fault code cannot be fixed by an end user. If you are not qualified to work on your boiler then the only option is to reset your boiler and hope it will work until you can get it looked at by a professional.
If you have over filled your system by mistake and suspect this may be the cause of the issue then you could try bleeding a radiator to get your system back in the normal pressure range.
The cost to repair the F75 fault code
The good news is that the F.75 issue can usually be fixed relatively economically and if you have this problem you generally do not need a new boiler!
As a general guide the F.75 fault code will usually cost somewhere between £145 and £320 to repair depending on the model of your Vaillant boiler and its age and assuming you don’t have any other issues with your boiler.
If the fault is being caused by a faulty pressure sensor and/or flat expansion vessel then the cost to repair is generally going to be on the cheaper end of the scale.
If the fault is being caused by a faulty pump then the cost to repair is typically going to be on the higher end of the scale as the pump is one of the more expensive components.
If the fault is being caused by a faulty printed circuit board then expect the cost to repair is generally going to be in the same region as what a faulty pump would cost to replace.
If the fault is being caused by a faulty wiring harness then expect the cost to repair to be somewhere in between the cost of a faulty sensor and a faulty pump or printed circuit board.
Is your boiler safe to use?
Yes your boiler should be safe to use with an intermittent F.75 fault code if you have to keep resetting it.
However, my advice would be to get this fault code investigated at your earliest convenience by a suitable Gas Safe registered heating industry professional who is familiar with Vaillant boilers as it is unlikely to keep working intermittently indefinitely.
How to prevent the F75 fault code
Regular maintenance is generally the key to avoiding the F.75 fault code and other problems. This can be achieved by getting your boiler serviced annually by someone who is familiar with Vaillant boilers.
Routine boiler servicing allows for faulty parts such as the pressure sensor to be identified and potentially replaced as part of preventative maintenance before they fail and cause problems.
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I offer maintenance services for most Vaillant boilers and I cover a large part of South Yorkshire including most of Sheffield, Rotherham and Barnsley.
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