Vaillant F75 fault code explained

One of the most common Vaillant boiler fault codes is the F75 error code.

If you have a Vaillant ecoTEC boiler there is a good chance you may experience this fault code at some point.

This fault code can cause your Vaillant boiler to stop working, leaving you without central heating or hot water.

The following clip is of a first generation Vaillant ecoTEC boiler with a failing pump and an intermittent F75 fault code.

If you look in the Vaillant ecoTEC installation manual under the F75 fault code it states the following;

“Insufficient pressure jump detected when starting the pump – Insufficient pressure jump detected when starting the pump”.

On Vaillant ecoTEC combi and system boilers they have a pressure sensor.

The pressure sensor is a safety device and on a Vaillant boiler it does two jobs.

First it is designed to tell how much pressure is in the boiler – the boiler will not work if it thinks the pressure is too low.

Secondly if the boiler is satisfied it has enough pressure then it will upon demand the boiler will go through the ignition sequence and attempt to fire up to provide hot water or heating.

Before the boiler fires up it wants to know if the pump is working or not. It can tell if the pump is running as the pump will create a rise in pressure if it is working sufficiently.

Upstream of the pump is the pressure sensor, which is located on the return pipe between the pump and the primary heat exchanger(located on the flow pipe manifold after the primary heat exchanger on early ecoTEC models).

If the pump is working sufficiently, the rise in pressure will be detected by the pressure sensor and relay this information back to the printed circuit board(pcb) via a small change in voltage.

If the pressure rise is sufficient, the printed circuit board will assume the pump is working sufficiently for the boiler to work safely and go the next part of the ignition sequence.

If no rise in pressure is detected the printed circuit board will run the pump three times and if still no pressure rise is detected, the printed circuit board will assume the pump is not running and display an F75 fault code and go no further.

This is a fail safe built into Vaillant ecoTEC combination and system boilers to ensure that they work safely.

Not all boilers have this kind of failsafe. A lot of boilers will fire up and try to operate and overheat even if the pump is not running, as they have no way of knowing whether the pump is running or not.

The F75 fault code on a Vaillant ecoTEC boiler can be caused by several things, including a faulty pump, faulty pressure sensor, faulty printed circuit board, faulty wiring harness or an over pressurisation of the boiler.

An over pressurisation of a boiler can be caused by a faulty expansion vessel, a faulty filling loop or a customer over pressurising their boiler by mistake whilst trying to add pressure.

This is why it is important to get a suitable Gas Safe registered heating engineer with experience on Vaillant ecoTEC boilers, otherwise you could waste money fitting parts that are unnecessary.

When to call a gas engineer to fix your boiler

If you are experiencing the F75 fault code on your Vaillant boiler, it is important to take action as soon as possible. While some issues can be resolved by homeowners themselves, others require the expertise of a qualified Gas Safe registered heating engineer.

Because the F75 fault code can be caused by several different faulty parts, it is extremely important to get a suitable heating engineer with experience on Vaillant ecoTEC boilers, otherwise you could end up wasting money fitting parts to your boiler that are unnecessary.

Often you will be able to reset your boiler if its showing and F75 fault code, but in general this is just a short term solution and usually your boiler will stop working altogether at some point, leaving you without hot water and heating.

So it usually best to get a qualified heating engineer to have a look at your boiler at your earliest convenience.

How to prevent the F75 fault code

A lot of the time this fault code can be prevented by getting your Vaillant boiler serviced regularly, ideally on an annual basis. Getting the right engineer to service your boiler is key.

While servicing your boiler a good engineer with experience working on Vaillant ecoTEC boilers should be able to tell if your pump coming to the end of its life, or if the pressure sensor is reading accurately or is likely to cause problems in the future.

As such they can recommend replacing the parts as a preventative maintenance measure, to ensure your boiler doesn’t stop working with an F75 fault code when you need it most – like in the middle of winter.

Vaillant ecoTEC boilers affected by the F75 fault code

The F75 fault code on Vaillant ecoTEC boilers only affects combination boilers and system boilers fitted with a pressure sensor. This fault code does not affect heat-only boilers in the 400 Series range as these boilers don’t have a pressure sensor.

So this fault code can be found on any Vaillant ecoTEC Pro combination boilers, any ecoTEC plus 800 Series combination boilers or any ecoTEC plus 600 series system boilers. Below is a list of ecoTEC boilers affected by the F75 fault code;

• ecoTEC Pro 24 and ecoTEC Pro 28 natural gas combination boilers
• ecoTEC Plus 800 Series 824, 828, 831, 837 and 937 natural gas combination boilers
• ecoTEC Plus 800 Series 825, 832, 835, 838 and 938 natural gas combination boilers
• ecoTEC Plus 600 Series 612, 615, 618, 624, 630 and 637 natural gas system boilers

Frequently asked questions

Can I repair the F75 fault code myself?

No unfortunately not, in most cases repairing the F75 fault code will require removing the cover of your boiler to replace parts which you are not legally allowed to do unless you are a Gas Safe registered heating engineer. You may be able to reset your boiler and it may work for some time.

Is the F75 fault code dangerous?

No the F75 fault code is not inherently dangerous. Modern Vaillant boilers are designed with fail safes in place to make sure that the boiler will only work if it safe to do so.

However there are some instances where a faulty printed circuit board can cause the pump to stop running whilst the boiler is fired up and running, which would cause the boiler to over heat.

If your boiler is over heating or you think it is over heating the it is probably best not to keep resetting your boiler as you could cause damage to it. In this instance it is generally best to leave your boiler turned off until a suitable engineer can have a look at it.

Is my boiler showing an F75 fault code worth repairing ?

Yes most of the time your broken Vaillant ecoTEC boiler displaying an F75 fault code will be worth repairing. Obviously the cost to repair your boiler will be determined by which parts need to be replaced.

You would need a competent, Gas Safe registered heating engineer to have a look at your boiler and make an assessment to determine exactly which parts might need to be replaced.

Before replacing your boiler it is always worth getting a suitable Gas Safe registered heating engineer with experience working on Vaillant ecoTEC boilers to make an assessment of your boiler so you can determine whether it is worth fixing or not.

Post written by Rich the boiler guy