Vaillant Boiler F75 Fault Code
The Vaillant fault code F75 boiler Low Pressure Water Sensor or the pump problem Q & A or require an engineer for an emergency boiler repair.
The Vaillant Boiler Fault Code F75 Error Common Q&A
Vaillant Boiler F75 Fault Code
- What does it mean if my Vaillant boiler is displaying a F75 fault code?
- What parts in the boiler can lead to the F75 fault code being displayed?
- Will resetting the boiler clear the fault code?
- Why would a faulty low water pressure sensor cause the boiler to lock out?
- What can be done to highlight a sensor fault, and to fix it?
- How can loose or damaged connections on the pressure sensor be fixed?
- What if it’s water damage that’s caused the F75 fault code?
- Is there a way to check for water damage on a DIY basis?
- What can be done to fix water damage and the F75 fault?
- How can the central heating pump get blocked and cause the F75 fault?
- Will a blocked heating pump need to be replaced to clear the F75 fault?
- Will having a power flush stop the heating sludge from coming back?
- Are there ways to protect against future sludge, and stop the F75 from occurring?
- How can the expansion vessel cause a problem, and the F75 fault code to be displayed?
- How can the expansion vessel be fixed?
What does it mean if my Vaillant boiler is displaying a F75 fault code
According to Vaillant, the F75 fault code will be displayed when there’s an issue with the low water pressure sensor, or with the pump.
What parts in the boiler can lead to the F75 fault code being displayed
The F75 fault will be displayed when:
- The low water pressure sensor is faulty, or has defective wiring
- The pump isn’t running due to being faulty, blocked or being fed inadequate pressure (0.05 bar within 10 seconds of start up)
- The expansion vessel isn’t sufficiently pressurised
Will resetting the boiler clear the fault code
On occasion, resetting a boiler where the fault is intermittent, will clear the fault code for a short while. For instance, loose connections will provide signals that mean the boiler works, then suddenly doesn’t.
However, it’s important to get a Gas Safe engineer to fix the problem and do safety checks, before resetting the boiler.
Why would a faulty low water pressure sensor cause the boiler to lock out
The low pressure water sensor is designed to detect drops in pressure. A drop in pressure signifies a leak.
Not only will this leaking water cause property damage, but it can cause damage to internal boiler parts. For instance, the pump is put under excess strain, and that causes excessive wear to the motor.
The boiler locks out (usually below 0.6 bar) to protect these components.
If the pressure sensor is incorrectly detecting low pressure, it will lock out, even if the pressure is correct (around 1.5 bar).
What can be done to highlight a sensor fault, and to fix it
Old boilers are prone to having parts failing, and the low pressure water sensor isn’t an exception.
The unit itself can be tested but generally, there are two causes of a fault here:
- Loose or damaged connections
- Water damage
How can loose or damaged connections on the pressure sensor be fixed
Loose and damaged connections will cause the intermittent signals we talked about earlier. And, that causes intermittent operation.
A visual inspection can highlight all the potential culprits. These need to be secured, or replaced.
And, all the remaining connections will need to be tested. Not all faulty wiring can be highlighted by visual inspections.
What if it’s water damage that’s caused the F75 fault code
Water damage is a big problem for all boilers, not just Vaillants, and not just old ones.
One of the most common ways a boiler gets water damage, is when the seals on the pump start leaking.
A slight drip from the pump won’t stop the pump or boiler working. What it will do, is create condensation. This is going to settle on electrical components.
Where there’s damaged (and potentially exposed) wiring, or an electrical unit that’s not 100% sealed, it’s going to penetrate and cause a whole host of problems.
Is there a way to check for water damage on a DIY basis
The most obvious sign that your boiler might be suffering from water damage is small drips or pools of water below your boiler.
You can guarantee that not all water has escaped from the boiler and there’s still some inside, finding it’s way into electrical components.
What can be done to fix water damage and the F75 fault
The first thing to do is the isolate and fix the leak. As a boiler leaks, it loses pressure. A lot of people just keep topping up their boiler using the filling loop, not realising this water is dripping over expensive boiler parts.
If it’s the pump seals causing the issue, these will need to be replaced, before fault finding electrical components and eventually clearing the F75 fault code.
How can the central heating pump get blocked and cause the F75 fault
Water damage is a big killer of boilers, but it’s not the only one.
Every single heating system will have an element of “heating sludge” in it. That’s a combination of minerals in water, and particles that come from the interior of pipework, radiators and towel rails.
Essentially, it’s rust.
This rust sloshes around the heating system, until it forms a black, thick and sludgy water. And, it’s this water and the particles in it, that cause blockages.
If there’s a F75 fault code on your Vaillant, there’s a good chance that it’s the heating sludge that’s to blame.
Will a blocked heating pump need to be replaced to clear the F75 fault
If the heating pump is in reasonable condition, there’s no need to replace it.
They’re simple units to dismantle. So, the boiler engineer will need to dismantle the pump, clear the blockage and refit the pump.
The only time a replacement should be considered is if it’s showing other signs of damage or wear.
For instance, the shaft’s bearings are loose and there’s a slight leak from the seals. This becomes time consuming and expensive to fix. There’s little point investing lots of cash in an old pump unit.
Will having a power flush stop the heating sludge from coming back
There’s not a full proof way to get rid of 100% of heating sludge in your system. But, there are ways to remove most of the sludge, and to stop most future heating sludge build up.
There are two options when cleaning a heating system to remove sludge:
- Power flush
- Hot flush
A power flush is more suited to newer heating systems. It flushes the system using pressure. The problem here is, there’s rarely enough heating sludge to need a full-on power flush. The most stubborn sludge takes years to build up.
On the flip side, older heating systems rarely withstand this pressure and it can induce leaks.
So, most of the time a hot flush will be more suited.
The engineer will add cleaning chemicals and flush the sludge out of the system with the heating on.
The heat helps to remove the tougher heating sludge, without using a power flush unit that increases pressure.
Are there ways to protect against future sludge, and stop the F75 from occurring
Flushing a heating system is only half of the job. The system now needs to be protected. And, doing so is incredibly simple:
- Add central heating inhibitor, which breaks down heating sludge
- Fit a scale reducer (in hard water areas) to catch limescale
- Install a magnetic boiler filter (to catch sludge broken down by the inhibitor)
- Have both the scale reducer and boiler filter cleaned with each boiler service
This is more than enough to protect boiler parts from heating sludge. And, the combination of a hot flush and the above protection can actually improve the efficiency of your heating system; so, you save cash too!
How can the expansion vessel cause a problem, and the F75 fault code to be displayed
The expansion vessel in a central heating system is designed to relieve pressure. This stops pipes and connections from bursting.
As pressure rises on closed systems, the expansion vessel will allow excess pressure to escape. But, these vessels need to be pressurised.
If they’re below operating pressure, the pressure of the heating system will need to be much higher than it should before the expansion vessel works
Essentially, the expansion vessel will only work after internal heating pressure is above what it should be.
How can the expansion vessel be fixed
Assuming the vessel itself isn’t damaged, the pressure will need to be topped up.
Your Gas Safe engineer will be able to check pressure, top it up, and reset your boiler to clear the F75 fault code.
Other Vaillant Fault Codes And Error
If your looking for the list of error codes relating to the Vaillant boiler then please read the article Vaillant Boiler Fault Codes And Cures