Glow-Worm Boiler F10 Fault Code
The Glow-Worm fault code F10 relates to the thermistors that monitor central heating and here we have Q & A or require an engineer for an emergency boiler repair.
The Glow-Worm Boiler Fault Code F10 Error Common Q & A
Just below, we have a list of common questions relating to the F10 fault code on the Glow-Worm Boiler.
- What does the F10 fault code mean on my Glow-Worm boiler?
- What is a thermistor?
- If I reset my boiler, will this fix the F10 fault code on my Glow-Worm boiler?
- What’s the most likely cause of the F10 fault code being displayed?
- The thermistors aren’t the problem, what else needs to be checked for faults?
- Could a circulation fault be the root cause of the F10 fault code being displayed?
- How can the pump be tested for electrical faults?
- What would air locks in radiators have to do with the F10 fault code being displayed?
- How would the pump on my boiler get blocked?
- How do I know if my pump is on the incorrect speed setting?
- What is the heat exchanger on my boiler, and how could this cause the F10 fault code to be displayed?
What does the F10 fault code mean on my Glow-Worm boiler
When your Glow-Worm boiler has a problem, it will lock out and display a fault code.
The lock out will help isolate the boiler from being dangerous, as well as protecting internal components from further damage. And, the fault code displayed helps a repair company quickly diagnose what the problem is.
In the case of the F10 fault code, the problem stems from the thermistors that monitor central heating.
What is a thermistor
Your boiler has various sensors, the thermistors are one of these types of sensors.
A thermistor will monitor both the flow (water leaving the boiler after it’s been heated) and the return (water returning to the boiler, ready to be reheated).
The readings from the thermistors are measured in ohms. For instance, at 20C, we’d expect a reading of around 12kohms.
This information is constantly sent back to the printed circuit board, which will then switch the resistance reading into a temperature reading. From these readings, the boiler can recognise if water needs to be heated further, or whether to cut fuel supply to the burner to stop water overheating.
In the case of the F10 fault code, it’s likely the boiler’s PCB has recognised a problem, whereby water isn’t at the correct temperature, and there’s a discrepancy between the flow and return resistance readings.
As an example, the differential between the two thermistors might be too high, the flow might be too hot, or the there might not be a big enough increase in temperature after the boiler has fired up.
If I reset my boiler, will this fix the F10 fault code on my Glow-Worm boiler
Resetting your boiler isn’t going to fix the problem at hand. The reset function on Glow-Worm boilers is designed to be used after the problem has been found and fixed. To do this, you’ll need to speak to a Gas Safe registered boiler repair company.
Resets can trick a boiler into temporarily working. Although it’s likely the PCB will quickly recognise the problem hasn’t been fixed and lock out again, working for just a few minutes could cause further damage to expensive parts. And, that’s only going to add to the cost of repairs.
What’s the most likely cause of the F10 fault code being displayed
The most likely cause of the F10 fault code being displayed, is a faulty thermistor. These are fragile electrical parts. And, that means a slight knock, or exposure to the smallest amount of moisture, could damage them.
So, the first thing your boiler engineer is going to need to do, is the test the thermistors on your boiler. They’ll be able to do this using electrical testing equipment, such as a multi-meter. They’ll be looking for a reading of around 12,000 ohms when at 20C. If the reading isn’t close to this, or there isn’t any resistance reading and a possible short circuit, they’ll need to replace the offending thermistor.
Having readings that are non-existent or inconsistent, are going to lead to the boiler working sporadically.
The thermistors aren’t the problem, what else needs to be checked for faults
If the thermistors themselves aren’t the problem, the next step is to assess the condition of electrical wiring and connections, especially the wiring harness from the PCB to the thermistors. Any loose or damaged connections on this part of the circuit will lead to intermittent signals being passed to the PCB, and that’s going to cause a whole host of problems.
Like the thermistor, your boiler repair company will be able to test wiring and connections using a multi-meter. Any damaged sections of wiring will need to be fixed, and loose connections secured, to ensure that the signals being passed to the PCB are perfect.
Could a circulation fault be the root cause of the F10 fault code being displayed
A circulation related fault could be the problem here, rather than the thermistor. In this case, the thermistor’s readings are correct, but, those readings are outside the working tolerance that the manufacturer has determined as being reasonable. And, that means that when these readings reach the PCB, the PCB locks out the boiler.
Anything that affects the circulation of water in the heating system could be to blame. And, that includes things such as:
- Electrical faults on the pump
- Air locks in radiators
- Blockages or air locks in the pump
- Pump set to the incorrect speed
- Blockage in the heat exchanger
How can the pump be tested for electrical faults
Just like all electrical components, the pump can be tested using a multi-meter. Whereby damage is small and easy to fix, a repair is usually the most cost-effective option.
However, if the pump has lots of electrical damage, and it looks worn, a replacement might be a better long-term solution.
Typically, a new pump is going to cost in the region of £250 to replace. That’s the price including labour, and a pump from a leading brand such as Grundfos.
What would air locks in radiators have to do with the F10 fault code being displayed
Whilst the most likely cause would be a thermistor fault, circulation faults need to be ruled out. And, air locks of any kind, can cause circulation faults.
Air locks act like blockages, and they need to be removed. Your heating engineer can easily remove air locks from your system.
On each radiator and towel rail, they’ll be a bleed valve. As they open these valves, they’ll start hissing. Once they stop hissing, water will begin to dribble out. This is an indicator that the air lock has been removed, allowing water to flow around the system more freely.
How would the pump on my boiler get blocked
Like towel rails and radiators, the pump in your boiler can be subject to airlocks. Your Gas Safe engineer will need to remove the casing to access the pump, and then bleed it using the specifically designed bleed screw.
But, if no air is released from the pump, there’s a good chance there’s an internal blockage. Internal blockages usually come in the form of heating sludge.
This is essentially, rust that’s broken off from the inside of pipework, radiators and towel rails. As it circulates around the system, this heating sludge lodges itself just about everywhere, including the heating pump. And, this is enough to cause a small blockage and circulation fault.
So, your boiler engineer will need to remove the heating sludge from the pump. But, they’ll also want to make sure that this doesn’t happen again.
First, they’ll want to hot flush your system with chemicals, removing most of this sludge. And, when they top up your heating system with water, they’ll be adding central heating inhibitor that breaks down this sludge.
Finally, they’ll fit a magnetic boiler filter. After the inhibitor breaks down the sludge, it’s the filter’s job to catch it. These filters can then be cleaned out with an annual boiler service.
How do I know if my pump is on the incorrect speed setting
You’ll need your boiler engineer to assess your heating system, and then check the speed setting on your pump. If water isn’t being pump out of the heat exchanger fast enough, you’ll see a big differential between the flow and return thermistors, and the boiler will lock out.
Different settings are designed for different heating systems. For instance, a small heating system might only need the pump to be on its slowest speed setting.
Your heating engineer will be able to adjust the speed setting on the pump if it’s incorrect.
What is the heat exchanger on my boiler, and how could this cause the F10 fault code to be displayed
The heat exchanger is what enables heat to be transferred from a flame, to the water. So, when there’s a problem with the heat exchanger, water might not be heated enough, or it might heat up too much. When it passes through the thermistor, the PCB recognises that something is wrong.
If you can hear small popping or whistling sounds on the heat exchanger, there’s a good chance that’s due to limescale build-up. These sounds are related to kettling; water is overheating, and air is being released.
Where limescale settles, water will burn hotter than it should. So hot sometimes, that air bubbles are released.
You’ll need to get the heat exchanger cleaned, to rid it of all limescale. A wise idea would be then to fit a limescale reducer.
Other Glow Worm boiler issues
For more boiler issues regarding the Glow Worm then please visit the Glow Worm Boiler Problems And Cures page.