Glow-Worm Boiler F7 Fault Code
The Glow-Worm fault code F7 relates to the hot water thermistor and here we have Q & A or require an engineer for an emergency boiler repair.
The Glow-Worm Boiler Fault Code F7 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 F7 fault code mean on my Glow-Worm boiler?
- Can I reset my boiler to clear the F7 fault code?
- What are thermistors?
- What is the most likely cause of the F7 fault code being displayed?
- How will my boiler engineer know if there’s an electrical fault with my boiler?
- How do air locks form in boilers, and how can they contribute to the F7 fault code being displayed?
- Can air locks in boiler pumps be removed?
- Why is my boiler overheating?
- How can I combat limescale in my boiler?
- What pump faults could be contributing to the F7 fault code being displayed?
- Can heating sludge be removed from my boiler’s pump?
What does the F7 fault code mean on my Glow-Worm boiler
When your Glow-Worm boiler develops an issue, it’s the printed circuit board (PCB) that tries to figure out what the problem is.
After it does, it’s going to display a fault code on the display panel (F7, in this case). The idea behind fault codes, it to help your boiler engineer to quickly determine what the problem is, making fixing that problem, much quicker than it would be otherwise.
The F7 fault code on your boiler is related to the hot water thermistor. There is a sensing issue in your Glow-Worm boiler whereby the temperature is too hot, too cold, or a temperature reading isn’t being logged at all.
Can I reset my boiler to clear the F7 fault code
A reset isn’t going to change the fact that there’s a problem with your boiler. The reset function should only be used when the boiler has been fixed.
And, gas appliances should only be worked on by Gas Safe engineers. If you have a fault code being shown on the display panel, it’s wise to speak to a boiler repair company as soon as possible. There’s a chance that if the boiler hasn’t locked out, it could be damaging internal components.
What are thermistors
The thermistors on your boiler feed back information to the PCB. The thermistor for hot water will monitor the resistance reading as water leaves the boiler. The hotter the water is, the lower the resistance reading is. This information is passed onto the PCB, which can then convert the resistance reading into temperature.
The idea behind this, is to make sure that hot water is always at the desired temperature. When water is too hot, the PCB tells the gas valve to reduce fuel supply to the burner, dropping the temperature of the water. And, if it’s not warm enough, the gas valve will open to supply more fuel to the burner.
What is the most likely cause of the F7 fault code being displayed
The F7 fault code isn’t as specific as it might seem. There’s been a temperature sensing issue, and there’s a good chance it’s the thermistor that is faulty. However, anything that could cause the temperature on the thermistor to not log the correct temperature, needs to be checked.
So, the first thing for your Gas Safe boiler repair company to do, is to test the thermistor using a multi-meter. If there’s a lack of, or intermittent, power to the thermistor, it’s likely it needs replacing, or the connections and wires need repairing.
If the thermistor seems in good condition, it’s likely that there are other things stopping the boiler getting hot water up to temperature, which leads to a F7 fault being logged. This could be things such as:
- Air locks in the boiler
- Limescale build-up causing an overheat
- Pump faults
But before checking these parts, your boiler engineer will need to eliminate electrical faults as being the problem.
How will my boiler engineer know if there’s an electrical fault with my boiler
As with most fault codes, electrical issues can be the root cause of the F7 on many occasions. And, a good place to start, is with the PCB.
It’s the PCB that controls almost every electronic component in the boiler. And, it gives and receives signals to all these components. So, when the PCB fails, or starts to work intermittently, it’s likely the boiler is going to fail or work intermittently, too.
And, to add to the problem, it’s the PCB that decides which fault codes should be displayed on your boiler. If the PCB isn’t working correctly, the fault code might not be the most relevant one.
Like the thermistor, your boiler engineer can check the PCB for visual damage, and then test it using a multi-meter. If there are signs of burnt out connections or lack of power, it’s likely that the PCB will need to be replaced.
Unfortunately, this isn’t a cheap component to replace. You should expect to pay around £500 for a PCB replacement.
How do air locks form in boilers, and how can they contribute to the F7 fault code being displayed
The most likely cause of an air lock in your Glow-Worm boiler, is going to be in the pump. The pump is a component that is put under an immense amount of pressure during the boiler’s operation, so over time, they do develop faults.
When air locks occur, they act much like a blockage. They’re going to restrict the flow of water out of the pump. And, that’s going to lead to huge temperature fluctuations in hot water. This is recognised by the PCB, after getting resistance readings from the thermistor. Eventually, that’s going to lead to the boiler locking out and displaying the F7 fault code.
Can air locks in boiler pumps be removed
As we’ve already mentioned, you shouldn’t be working on a boiler without Gas Safe accreditation. But, your boiler repair company will be able to remove the air lock from your boiler quite easily.
On most modern boiler pumps, there’s a bleed screw. This screw is specifically designed to remove air locks. Your boiler engineer will open the screw slightly, and a hissing noise will occur. This is the air escaping from the pump. Once the hissing noise changes to a slight dribble of water, that’s a sign that the air has been completely removed from the boiler.
Why is my boiler overheating
Blockages are also going to affect the temperature of hot water leaving your boiler. A typical example of a reason why a boiler overheats, is a heat exchanger that’s got a build-up of limescale on it.
Limescale attacks all parts in a central heating system. But, it seems that the heat exchanger in your boiler tends to be the component that gets hit the hardest.
Where limescale builds-up on the heat exchanger, it burns much hotter than the rest of the water in the system. This leads to water being overheated. When it is pumped from the boiler and past the thermistor, the thermistor’s reading notifies the PCB that there’s a problem that could be causing hot water to be scalding hot from taps and showers.
How can I combat limescale in my boiler
The first thing to do, is to hot flush the central heating system with chemicals designed to remove limescale.
After this is done, your boiler engineer can top up the system using central heating inhibitor, to help break down limescale. And, they can then fit a limescale filter. This catches limescale, rather than allowing it to build-up on expensive boiler components.
One thing your boiler engineer will need to consider, is whether the boiler’s heat exchanger has been damaged by limescale. On some occasions, the overheat can cause the heat exchanger to crack and leak. If this is the case, the heat exchanger will need to be replaced. And this can cost more than £400 on many Glow-Worm boilers.
What pump faults could be contributing to the F7 fault code being displayed
Any circulation fault is going to cause the speed in which water circulates, to differ from what’s normal. And, that’s going to mean that water gets the to thermistor, too fast/too slow. In turn, that’s going to mean that water is too hot or too cold.
The pump is the key component in your boiler, when it comes to circulating water to taps and showers. If there’s a fault on the pump, that could be what’s causing the F7 fault code to be displayed, not the thermistor.
Before checking for faults, your boiler engineer will need to ensure the pump is on the correct speed setting. Typically, new pumps have 3 speed settings. Having the wrong setting on your pump, could mean that circulation is affected is a negative way.
They’ll then test for electrical faults using a multi-meter, and check for air locks (mentioned above), and blockages in the form of central heating sludge.
Can heating sludge be removed from my boiler’s pump
Sludge is rust that breaks off from radiators and pipework. As it sloshes around the heating system, it breaks down to create dirty heating water. This can cause blockages, and ruin boiler parts.
The sludge can be used by hot flushing the system with chemicals. Manually removing any excess sludge from the pump will also help.
Once removed, the boiler can be protected by dosing the system with central heating inhibitor, and fitting a magnetic system filter, specially designed to catch heating sludge.
Other Glow Worm boiler issues
For more boiler issues regarding the Glow Worm then please visit the Glow Worm Boiler Problems And Cures page.