Glow-Worm Boiler F6 Fault Code
The Glow-Worm fault code F6 relates to a problem detected by the printed circuit board (PCB) and here we have Q & A or require an engineer for an emergency boiler repair.
The Glow-Worm Boiler Fault Code F6 Error Common Q & A
Just below, we have a list of common questions relating to the F1 fault code on the Glow-Worm Boiler.
- What does the F6 fault code mean on my Glow-Worm boiler?
- What is the role of thermistors on my boiler?
- If I reset my boiler, will that fix the problem with the thermistor?
- What problems can cause the F6 fault code to be displayed?
- How will my boiler engineer know if the thermistor is to blame?
- What does limescale on the heat exchanger have to do with the F6 fault code?
- If my heat exchanger can be salvaged, is there any way to combat limescale in the future?
- How will my boiler engineer know if there’s a problem with the pump?
- How do I know if I have low water pressure?
- How do boiler leaks occur and cause the F6 fault code to be displayed?
- How do I know if I need to replace my boiler?
What does the F6 fault code mean on my Glow-Worm boiler
When your Glow-Worm boiler recognises that there’s a problem, it will lock out and display a fault code. The lock out is to ensure that no further damage is caused to internal components. And, the fault being displayed (F6 in this case), helps your boiler engineer to determine what the exact problem is.
The F6 fault code on your Glow-Worm boiler, means that there’s a problem detected by the printed circuit board (PCB), at the point of the central heating flow thermistor. This doesn’t necessarily mean that the thermistor is to blame, but the temperatures being logged, are not within tolerance.
What is the role of thermistors on my boiler
There are a range of thermistors on your boiler, located at both the point of flow (water leaving the boiler) and return (water returning to the boiler, after traveling around the central heating system).
The role of the thermistors on boilers, is to measure resistance (in ohms). This reading is then converted to a temperature by the PCB, to determine if the boiler is operating within tolerances. And, when it’s not, or no reading is given, it’s going to lock out and display a fault code.
If I reset my boiler, will that fix the problem with the thermistor
Resetting your boiler isn’t going to fix the F6 fault code on your Glow-Worm boiler. The reset function on boilers should only be used after the problem has been diagnosed by a Gas Safe engineer. Once they’ve found the issue and fixed it, they’ll then reset the boiler on your behalf.
Working on gas boilers should only be done by Gas Safe repair companies, so you should call one right away.
What problems can cause the F6 fault code to be displayed
Fault code descriptions in boiler manuals are rarely clear. And, this is a perfect example. Most people jump to the conclusion that the fact the problem is highlighted as the thermistor, that’s the faulty component that needs replacing. Although that can sometimes be the case, there are other things that can contribute to the F6 fault code being displayed.
Anything that relates to the thermistor on the flow logging a temperature that is higher than it should be, could be the culprit.
So, it could be an overheat with a high temperature being logged, not a faulty thermistor.
That means checking for:
- Limescale build-up in the heat exchanger
- A blocked pump, or incorrect pump speed
- Low water pressure.
But, it’s not just flow related issues that could be causing the problem. The problem could be electrical, thanks to boiler leaks.
So, your boiler engineer will need to check electronic components for water damage, loose connections and damaged wires. This can cause things like the heat exchanger, pump and even the PCB to work intermittently, and cause the F6 fault code to be displayed.
How will my boiler engineer know if the thermistor is to blame
Whilst the thermistor isn’t to blame all the time, it’s still a potential culprit. So, your boiler repair company is going to need to test it.
Most boilers should read around 12,000 ohms at 20C, although this may vary from boiler to boiler. If the thermistor isn’t showing a reading, or isn’t close this the one mentioned above, it’s likely it needs replacing.
Replacing the thermistor and resetting the boiler will clear the F6 fault code and allow the boiler to be operational again.
But before replacing the thermistor, your boiler engineer will check the wiring harness. This connects the thermistor to the PCB. Without a solid connection there’s a chance that readings are incorrect, as are the signals being passed between the two components.
What does limescale on the heat exchanger have to do with the F6 fault code
If there’s any kind of overheat on the temperature of the flow water, this is going to cause a fault code to be displayed. And, limescale is something that can contribute to components on a boiler overheating. Where limescale settles, water tends to burn much hotter than it should. That’s going to mean that the water leaving the boiler (which passes through the flow thermistor), is much hotter than the temperature being demanded by the boiler.
If limescale hasn’t been present for a long period, it can be removed from the heat exchanger. However, on many occasions, the hot spot on the heat exchanger can lead to cracks. These cracks induce leaks, and that can cause a whole host of problems with other electrical components in the boiler.
The best option here is either to replace the heat exchanger, or for old boilers, replace the whole appliance. A typical heat exchanger replacement is going to cost around £450.
If my heat exchanger can be salvaged, is there any way to combat limescale in the future
Just like in dishwashers, limescale can be protected against. The first thing to do, is have your boiler engineer hot flush the system. They can do this using a chemical specifically designed to combat limescale.
Once this has been done, they can dose the system with central heating inhibitor, and fit a limescale filter. This helps to break down and catch any future limescale.
How will my boiler engineer know if there’s a problem with the pump
Once water reaches temperature, it needs to be pumped out of the heat exchanger. If the pump is blocked, or not set to the correct speed setting, it’s not pushing this water where it needs to be. This can lead to it overheating.
Pumps that are noisy or hot, show a sure sign of a blockage, or incorrect speed setting. So, first, your boiler engineer will want to check that the speed setting is correct. If it is, they’ll need to take the pump apart to see if there’s a blockage.
Typically, we find that the blockage comes from heating sludge. Whilst this can be directly removed from the pump, the build-up will re-occur if it’s not removed from the central heating system.
As with limescale, a hot flush will do the job. And, dosing the system with central heating inhibitor and fitting a magnetic system filter, will help to catch any sludge that enters the system in the future.
After everything’s been checked over, and the pump re-fitted, the pump needs to be bled of air, by your Gas Safe engineer. Any airlocks in a pump are going to act like blockages and hinder your pump’s performance.
If the blockage has caused damage to the pump, a replacement might be needed. A typical replacement from a leading pump brand such as Grundfos, is likely to cost in the region of £250.
How do I know if I have low water pressure
Like air locks and pump blockages, low water pressure doesn’t allow water to circulate quick enough. This can mean that water overheats, or the difference between the flow and return thermistor water temperature is too great.
You can check your boiler’s water pressure, on the pressure gauge, which is usually located on the display panel, near to where the F6 fault code is being displayed.
Most modern boilers work best at around 1.3 bar (check your owner’s manual). If your boiler is well below this figure, then this is likely the cause of the fault. And, if it drops below 0.5 bar, it’s likely to be showing a low water pressure related fault code, as well as the F6 fault code.
You can top up the boiler’s pressure using the external filling loop, that’s located below the boiler’s casing. However, if water pressure has been lost, it’s likely there’s a leak. And leaks can cause lots of damage, so you’ll want to get your boiler repair company to find and fix this leak, before topping up the boiler’s pressure.
How do boiler leaks occur and cause the F6 fault code to be displayed
Two parts mentioned already (the pump and heat exchanger), are the most common causes of boiler leaks. And, when they occur, they can cause electrical damage. That can lead to components not working correctly or failing completely.
If you’ve noticed pooling below your boiler, there’s a chance that one of these components is leaking.
The pump usually leaks due to excess pressure being put on its seals, whereas a heat exchanger leak will usually develop from limescale hot spots, which cause cracks.
Before fixing anything else, the leaks need to be found and fixed.
How do I know if I need to replace my boiler
As you can see, the root cause of the problem isn’t always easy to identify. And, when it is identified, the problem could be much more serious than just replacing a simple thermistor.
Your Gas Safe engineer will be able to fault-find to figure out all the problems with your boiler. From there, they can assess important components such as the PCB, pump, heat exchanger, thermistors and fan.
A general health check will help them determine whether the most cost-effective option here, is to repair or replace your boiler. Because, there’s little point spending £500+ on an old boiler, when a new one could be as little as £1,800.
Other Glow Worm boiler issues
For more boiler issues regarding the Glow Worm then please visit the Glow Worm Boiler Problems And Cures page.