Glow Worm F75 fault code is a common Glow Worm fault. It relates to the system pressure sensor and is usually easy to fix.
This article will explain everything you need about the F75 fault in a Glow Worm boiler and whether or not you need to call a Gas Safe registered heating engineer to get your central heating system back up and working properly
What does the F75 Glow Worm Fault mean?
The Glow Worm F75 code is called “Fault: Pressure sensor” in the Glow Worm manuals. This electronic component measures the water pressure that flows through it.
Pressure simply refers to the force at which hot water is being pushed through pipes in your central heating system. The volume of water in your system affects water flow and alters pressure.
After the water pressure sensor has read the pressure, it sends a signal to the printed circuit boards (PCB).
The PCB is the central control hub of the boiler. It confirms that every stage of the heating process was completed safely and successfully before allowing the next one to begin.
The water pressure sensor case is an example of a PCB wanting to know if the sensor can send a signal and if this signal indicates that the pressure is safe.
This reading is also displayed on the PCB at the front of your boiler in units called bars. You will see an average reading of 1 to 1.5 bars when your boiler is turned off.
This will rise to about 2.5% when it’s hot. This reading must be accurate if the pressure sensor is functioning properly.
Your boiler will shut down if it is unable to verify the water pressure.
The unit could still burn fuel at its normal rate if there was not enough water in the system. This could lead to dangerous conditions like overheating.
What Causes the F75 Glow Worm Fault.
Faulty pressure sensor
You could get the F75 error on a glow worm boiler is there is an electrical fault that can cause the water pressure sensor to stop working completely. The fault code on the screen may indicate if the sensor has a problem.
If you hear the heating process begin and the pressure reading on the front of the unit does not change, then it is likely that the sensor has failed. The F75 code will be displayed shortly thereafter.
How to fix a faulty pressure sensor
A multimeter is a tool that allows engineers to test electrical components such as the sensor.
It takes resistance readings that can be compared to the ideal specifications in order to verify that a component or its connections are working properly.
The cost to replace the sensor will vary depending on the model of your boiler, but the average estimate is between £180 and £280.
Blocked Pressure Sensor
The pressure sensors opening through which water flows are extremely small so they can easily get blocked by debris.
Heating sludge is a common cause of these types of blockages. It is a thick mixture made up of flaked rust, other debris, and other materials that collect in the pipes as water flows through them.
These pieces eventually clog and form a sludge that slowly moves through pipes. It can block any parts of the unit it comes into contact with.
How to fix if the Pressure Sensor has been blocked
A visual inspection will help you identify blockages, such as heating sludge, on the sensor. You can remove the sensor and clean it before reinstalling it. The sensor itself will not need to be replaced, unless it is damaged by the blockage.
Your engineer will have to remove the sludge from all other parts of the system. This may involve cleaning out any internal parts, but it will most likely require a “flush”.
This involves sending hot water along with specialist chemicals to the entire heating system. It dissolves heating sludge and other materials.
This service costs based on the number of radiators in your home, but usually prices start at £350.
It is a good investment to remove sludge from all parts of the system, not just the sensor. Otherwise, the problem could quickly return and cause more damage.
As an additional preventative measure, your engineer may also install a magnetic filter. These draw out water flakes to prevent them from building up.
They are usually less than £170 and can be replaced with every boiler service. These filters can prolong the boiler’s life and help to prevent costly damage.
This fault code refers to water circulation and could indicate a problem with the pump.
This large component is responsible for heating the water and pushing it out of the boiler. If the pump is operating properly, you will hear the boiler switch on and a vibration.
Depending on the problem, faulty pumps can cause unusual sounds like clanging or a loss of movement.
Pumps have a shaft and bearings that allow them to spin freely. If any of these parts get stuck, it can lead to pump failure.
Heating sludge in this area can cause problems with the main one being pump failure. However, blockages can also occur when there is air. This is called an “air lock”.
The bearings of an older pump may have been worn out by prolonged use
Modern pumps have many speed settings. If your pump was installed recently, it might be the wrong setting.
If your boiler and/or pump have been in use for a while, this is unlikely to be true.
Fixing a Pump Fault
If the speed setting was not correct during installation or recent work, it is the easiest problem to resolve. This can be quickly identified and corrected by an engineer.
You can deal with a heating blockage using the same process as above. Although an air lock is more complicated and costly, it can be fixed with a simpler approach.
An engineer will use a tool known as a bleed screw, which allows air to escape the pump until it starts to leak. After that the pump can be reinstalled.
Your engineer will recommend a replacement if any parts of the pump are damaged or worn. Once the pump stops working, it will fail again, even if the individual parts have been repaired. On average, new pumps cost between £250 and £300.
Low Water Pressure
This could mean that the water pressure may be too low. The Glow-Worm boiler F75 fault is often accompanied by a faulty sensor.
Boiler water pressure tends to fall below the required range about once a year. However, low pressure does not necessarily mean that there is an underlying problem and you do not need a Gas Safe registered engineer to fix this, you can do it yourself and it may remove any fault codes on your Glow Worm boiler.
How do I fix my own Glow Worm boiler with the F75 Fault?
While not all fault codes can be safely addressed by attempting to reset the Glow Worm boiler’s thermostat, you can for the F75 fault. For the F75 fault, hold down the power button for five second. A symbol that looks like a cross will flash on your display. The unit will then restart.
You can top up your pressure gauge if the reading is below 1 bar to determine if the fault code has been cleared.
- Make sure your boiler is at its lowest temperature
- Locate the two faucets under the boiler.
- Keep their hands parallel to pipes.
- The pressure gauge should not rise above 2
- Turn the taps to a perpendicular orientation and close them.
- Reset the boiler
This code suggests that low pressure may not be the sole cause. You will still need to have an engineer check the pressure sensor.
It is important to know how to maintain the boiler’s pressure. You will most likely need to do this at least once per year and should be at least completed during boiler servicing.
Maintaining the proper levels of heat will extend the boiler’s life and save you money in future repairs.
Does an F75 Glowworm boiler Fault code mean i need a new boiler?
You might find Vaillant boilers results when you search for Glow Worm fault codes but you will notice regardless that it doesn’t mean that you need a new boiler right away. However, if you have an old boiler, it may be time to consider this as blockages and parts failing usually lead to other problems.
Glow Worm was acquired by Vaillant in 2001. It is now an integrated brand. Glow Worm boilers and Vaillant boilers often have the same fault codes, as is F75.
But, they may not use the same system in all models. If you have a Glow Worm model, make sure to double-check before you follow the Vaillant boilers advice.