In This Guide
What Does the Vaillant F75 Error Code Mean?
F75 is Vaillant’s pump and pressure sensor fault code. It appears when the boiler fires the pump but the pressure sensor registers no change in pressure, so the boiler shuts down rather than run dry and damage itself. In plain terms, either the pump is not moving water or the sensor cannot read that it is. You will usually see it on ecoTEC and similar Vaillant models, and it normally leaves you with no heating and no hot water. It is one of the more common Vaillant faults 0800 Homefix attends across London and the South East, and while a couple of causes are safe to check yourself, most need a Gas Safe registered engineer. The sections below cover what triggers it, what you can safely do, and when it becomes an engineer’s job.
What Causes a Vaillant F75 Fault?
F75 sits between the pump and the pressure sensor, and the trigger can be either component, the water in the system, or the wiring linking them. The most common causes are set out below, with the check or repair each one calls for.
|
Cause
|
What happens |
Typical fix |
|
Faulty or seized pump |
The pump does not circulate water, so no pressure change registers when it starts |
A Gas Safe engineer tests and, if needed, replaces the pump |
|
Blocked or faulty pressure sensor |
Sludge or limescale coats the sensor, or it fails outright, so it cannot read the pressure change |
A Gas Safe engineer cleans or replaces the sensor |
|
Low system pressure |
The gauge sits below 1 bar, leaving too little water for the pump to move |
Top up through the filling loop to between 1 and 1.5 bar |
|
Air in the system |
Trapped air stops the pump moving water properly |
Bleed the radiators to release the air |
|
Sludge or debris in the system |
Corrosion sludge restricts circulation and clogs the sensor |
A Gas Safe engineer carries out a power flush |
|
Wiring or PCB fault |
A loose connection or a faulty PCB breaks the signal between pump and sensor |
A Gas Safe engineer inspects the wiring and the PCB |
The pattern is the same as with most boiler faults. Anything to do with the water in the system, the pressure and trapped air, is usually safe for a homeowner to check. Anything mechanical or electrical inside the boiler, the pump, sensor, PCB and wiring, is engineer territory and should not be opened up by anyone who is not Gas Safe registered.
How Do You Fix a Vaillant F75 Error?
There are a few safe checks worth doing before calling anyone, and they clear a fair share of F75 faults that come down to pressure or air rather than a failed part. Work through them in order.
First, check the pressure gauge. It should read between 1 and 1.5 bar when the heating is cold. If it is below 1 bar, the system is low on water and needs topping up. Use the filling loop, the small braided hose beneath the boiler, opening the valves slowly until the gauge reaches around 1.2 bar, then closing them again. If the pressure keeps dropping over days, there may be a leak somewhere in the system, which is worth having looked at.
Second, bleed the radiators. Trapped air can stop the pump circulating water properly and trigger F75. Working through the radiators with a bleed key releases that air, and you may need to top the pressure back up afterwards.
Third, reset the boiler once. Press and hold the reset button, the one marked with a flame symbol, then run a hot tap after a couple of minutes to see whether the pump kicks in and the boiler fires. If it settles, the fault has cleared. If F75 comes straight back, do not keep resetting. A boiler that repeatedly cannot register pump pressure has a genuine fault, and the next step is a diagnosis rather than another reset.
If those checks do not resolve it, the cause is the pump, the sensor or sludge in the system, and that needs a professional. You can arrange it through the 0800 Homefix boiler repair service.
When Should You Call a Gas Safe Engineer for an F75 Fault?
Call an engineer if F75 returns after you have confirmed the pressure is correct and reset the boiler, if the pressure will not hold, or if you can hear the pump making unusual noises or nothing at all. A persistent F75 almost always means the pump or pressure sensor has failed, or the system is heavy with sludge, and none of those can be put right without opening the boiler. By law, that work must be carried out by a Gas Safe registered engineer, so this is the point to stop the DIY checks and book one.
What Does an 0800 Homefix Engineer Do About an F75 Fault?
An 0800 Homefix engineer diagnoses an F75 rather than replacing parts on guesswork. They confirm the system pressure, test whether the pump is actually running and circulating water, and check the pressure sensor for sludge or failure, cleaning or replacing it as needed. Where the pump has seized or worn out they replace it, and where the real problem is a system full of corrosion sludge they will recommend a power flush to clear it and stop the fault returning. They also check the wiring and PCB for any break in the signal between pump and sensor. Every engineer is Gas Safe registered, and the team covers London and the South East seven days a week, 365 days a year, so an F75 does not have to mean a long wait without heating or hot water.
How Much Does It Cost to Fix a Vaillant F75 Fault?
0800 Homefix does not charge a call-out fee. The visit is charged as the first hour of labour, paid in advance, and any further repair work, whether that is a new pump, a pressure sensor or a power flush, is quoted and agreed with you before it begins, so nothing is a surprise once the engineer is on site. The exact rate and what the first hour covers are set out in full on the rates page. For peace of mind after the repair, 0800 Homefix guarantees its labour for 12 months, and the manufacturer guarantees any replacement parts for 12 months.
How Do You Prevent the F75 Fault Coming Back?
Most repeat F75 faults trace back to sludge and neglect, so two things prevent them. The first is an annual boiler service, which lets an engineer check the pump and pressure sensor and catch a weakening component before it fails. You can book this through Vaillant boiler servicing. The second is keeping the system water clean, since corrosion sludge is what clogs the pressure sensor and wears out the pump in the first place. A power flush on an older, sludged system, followed by a magnetic filter fitted to catch debris before it reaches the pump, makes a repeat F75 far less likely. It also helps to glance at the pressure gauge now and then and top the system up before it drops too low.
Frequently Asked Questions
How do I reset a Vaillant boiler after an F75 fault?
Press and hold the reset button, marked with a flame symbol, then run a hot tap after a couple of minutes to see whether the pump starts and the boiler fires. If F75 comes straight back, do not keep resetting. A repeat fault needs an engineer rather than another reset.
What water pressure should my Vaillant boiler be at?
The gauge should read between 1 and 1.5 bar when the heating is cold. If it is below 1 bar, top the system up through the filling loop until it reaches around 1.2 bar. If the pressure keeps dropping, there may be a leak in the system worth investigating.
Can I fix an F75 fault myself?
You can safely check and top up the pressure, bleed the radiators and reset the boiler once. Anything beyond that, the pump, pressure sensor, PCB or a power flush, must be handled by a Gas Safe registered engineer. If those basic checks do not clear it, 0800 Homefix can diagnose and repair the fault.
Is F75 caused by the pump or the pressure sensor?
It can be either. F75 means the boiler saw no pressure change when the pump started, which happens if the pump is not moving water or the sensor cannot read that it is. An engineer tests both to confirm which has failed, and sludge in the system can affect either one.
Why does my Vaillant boiler keep showing F75?
A recurring F75 usually points to a failing pump, a sensor clogged with sludge, or a system heavy with corrosion debris. Topping up the pressure will not fix any of those. It needs an engineer to diagnose the cause, and often a power flush to clear the underlying sludge.
Is an F75 fault an emergency?
It is not dangerous, but it normally leaves you with no heating or hot water, so it is worth resolving quickly. If basic pressure checks do not clear it, book a Gas Safe engineer rather than leaving the boiler locked out.
Spotted an F75 on Your Vaillant Boiler?
If the pressure checks and a reset have not cleared it, book an 0800 Homefix Gas Safe registered engineer. We cover London and the South East seven days a week, 365 days a year, with no call-out fee and a 12-month labour guarantee. Book online or call the team to get your heating and hot water back on.
Helpful Resources
- Gas Safe Register, to check any engineer’s registration: https://www.gassaferegister.co.uk/
- Vaillant’s own boiler support and fault code help: https://www.vaillant.co.uk/
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Editorial note: This article is intended as a general homeowner guide. All plumbing work on supply pipes should be carried out by a qualified, WaterSafe-registered plumber. If you suspect a gas leak, leave the property immediately and call the National Gas Emergency Service on 0800 111 999.
