Glow Worm Boiler Fault Problems And Cures

The Glow Worm boiler fault problems and cures Q & A or require an engineer for an emergency boiler repair.

The Glow Worm Boiler Fault Problems And Cures Common Q & A

Below we’ve written a guide covering the most common Glow-Worm boiler problems. We’ve mentioned fault codes and some potential fixes, to try and solve the issue at hand.

If you have a problem with your boiler, the DIY fix isn’t to reset it. A boiler reset is designed to be used after an engineer has found and fixed the problem, rather than as a cure.

There is a reason that your boiler has locked out in the first place. On some occasions, it’s to protect people in the property from danger (for instance, the boiler is leaking gas into the burner when turned on). And on other occasions it’s protecting internal boiler components from further damage, after a component failure.

When any problems with your Glow-Worm boiler involve taking the appliance apart, you’ll need to call an emergency boiler repair company. It’s only companies with Gas Safe accreditation that can work on gas appliances.

Here is a list of Glow Worm boiler fault finding code which you can click on and read further articles relating to the faults:

Why is my Glow-Worm boiler showing the F.22 fault code, and what can be done to fix the problem?

The F.22 on Glow-Worm boilers is the most common fault code we come across. The boiler’s printed circuit board (PCB) monitors a range of sensors, including a water pressure sensor. And, it’s the PCB that has recognised the reduction in system pressure.

Pressure in your heating system is derived from the amount of water that’s in it. There should be a pressure gauge on the front of your boiler, or just below the boiler casing.

Typically, you’d expect to see a pressure of 1-1.5 bar. 1.3 bar tends to be the perfect operating pressure for most modern boilers (but, always refer to your owner’s manual).

A boiler doesn’t have to be set at 1.3 bar to work. But, if the pressure rises above 3 bar, or in this case, drops below 0.5 bar, it’s likely the boiler will lock out.

The cause of pressure loss is most likely due to a leak. As water escapes from the system, pressure does too. With a low amount of pressure, parts like the boiler’s pump must work overtime, to circulate water around the heating system. And, that’s going to mean that these expensive components burn out quicker than they should.

This is where a lock out is important. If the boiler was to continue to operate, the pump would burn out quickly.

Your boiler engineer needs to find and fix the leak. This could be a boiler component, such as the pump or heat exchanger. On other occasions, the issue is something simple, like a soldered copper joint that needs re-soldering.

Some leaks can be much harder to spot than others. So, if the boiler is reset after fixing a leak and pressure continues to drop, there’s another leak that needs to be found and fixed.

Once your emergency boiler repair company is happy that the leak is fixed, they can top up your boiler using the external filling loop. By opening the filling loop, they’ll be adding water to your system, and therefore, pressure.

When the pressure gauge reaches 1.3 bar, they’ll close off the filling loop. Resetting the boiler at this stage, should clear the F.22 fault code, so your boiler is operational once again.

Why is my Glow-Worm boiler showing the F.23 fault code?

Another common fault code we come across with Glow-Worm boilers, is the F.23. The problem here is that the NTC thermistors have a temperature differential between them that is too high.

Each boiler has an NTC thermistor on the flow pipe (this is where heated water leaves your boiler), and another on the return (this is where water re-enters the boiler to be heated, after travelling around the heating system).

These are some of the many sensors in your boiler, that inform the PCB that the boiler is working within tolerances. When the maximum temperature differential between the two thermistors has been reached, it signifies that there’s a problem.

The most obvious place to start, is with the thermistors themselves. Your boiler repair company will be able to check both thermistors. First, they’ll want to check that they are fitted on the correct pipes and are securely installed.

If the installation isn’t the issue, they’ll need to test them for power using a multi-meter. Whereby the NTC thermistors have failed, replacements will be needed.

But, F.23 fault code problems aren’t always limited to the NTC thermistors. Anything that is negatively affecting the boiler’s ability to circulate water, could be causing the issue.

This could include a pump failure, an incorrect speed setting on the pump, or a blockage (in the pump, or due to air locks in the heating system).

To diagnose the problem, your boiler engineer can start with the basics. They’ll need to bleed your system of any air; they can do this via towel rails, radiators and the pump.

If there’s no air in the system, they’ll need to focus their attention on the pump’s operation. They can check the pump speed (most modern pumps have three speed settings), as well as checking that the pump is getting power. If it’s not getting power, a replacement will be needed; typical replacement costs are in the £250-300 range.

If all the above checks out ok, they’ll want to take apart the heating pump, looking for signs of sludge build-up. This sludge can easily block a pump, reducing its ability to circulate.

The heating sludge can be manually removed from the pump. But, it’s wise to flush it out of the system using cleaner, as well as dosing the system with inhibitor and fitting a boiler filter, to stop this from happening again.

If my boiler is showing the F.24 fault code, is it dangerous and can the problem be fixed?

When a Glow-Worm boiler shows the F.24 fault code, it means the temperature rise that’s being logged after start-up, is too fast. The root cause can sometimes be like that of the F.23 fault code mentioned above. However, here it’s more likely that the cause is a boiler component, rather than a temperature sensor, such as the NTC thermistors.

It’s unlikely that your boiler is dangerous as this problem doesn’t relate to gas supply, or a gas leak. However, your boiler should lock out to protect important internal components.

Don’t try and reset your boiler to clear the F.24 fault code. And, if the appliance hasn’t locked out, it makes sense to turn it off to protect components from expensive damage and call a Gas Safe registered engineer for help.

The most probable cause of the problem is a circulation issue. The main things your boiler engineer will need to check include the:

Pump, for airlocks and blockages
Pump’s speed setting
Boiler’s pressure
Radiators and towel rails for air locks

All these things can hinder the performance of your boiler and stop the appliance from circulating water correctly.

Your Gas Safe boiler repair company will start by bleeding all towel rails and radiators. If there’s air in the system, it’s also likely that there’s air in the heating pump. So, after ensuring that the boiler’s pressure is correct (filling up via the filling loop where necessary), they’ll need to remove the boiler’s casing and bleed the pump.

With all air removed from the system, they can check the speed setting on the pump. If the pump is on the lowest setting, this could be contributing to a fast rise in boiler water temperature.

Finally, they’ll want to check for evidence of heating sludge. A quick test would be to drain some system water from a towel rail, or the drain cock. If your heating water is dirty, it’s likely that this has blocked the pump, heat exchanger, and other components.

They’ll need to run a hot flush to clear most heating sludge. Preventive measures can be put in place, such as dosing the system with central heating inhibitor, and fitting a magnetic system filter.

However, if there’s a lot of sludge build-up, they may need to clear out the pump manually.

My boiler is showing the F.27 fault code on the display panel, what is the problem?

If the F.27 fault code is being displayed on your Glow-Worm boiler, it means the safety switch is off. The problem could lie with the safety switch itself, or it could be a problem with flame detection.

So, the first thing to do here, is to check the safety switch. Your Gas Safe boiler repair company will be able to check that the wiring and connections to the safety switch are secure. Assuming they are, they can then test the safety switch for power. If it’s showing no power, that’s most likely the culprit, and a replacement is going to clear the F.27 fault code.

However, the fix isn’t always this simple. The problem here could be due to loose or damaged electrics, or electronic components. Your boiler engineer will need to visually inspect all connections, wires and components that are linked to flame detection. A typical example would be the flame sensor.

Once they’ve checked all the basics, they’ll move onto the gas valve. Gas valves are mechanical components, and over time, they can stick; they don’t operate freely, as they should.

In this case, there’s a chance that the gas valve is sticking partially or fully closed. And, that means that not enough gas is getting into the burner, causing a shortage of gas supply. That’s enough to stop the burner from igniting, and therefore, no flame is present.

On some occasions, this could be linked to a faulty PCB. It’s the PCB that gives and receives signals from sensors. If the signals it’s giving/receiving are incorrect due to the fault, a flame might be present, but the PCB isn’t getting that signal. So, if all else fails, your boiler engineer will need to check the PCB’s operation.

This is always a last resort. The PCB is the most expensive component in a boiler and can cost upwards of £400 to replace.

My boiler is showing the F.28 fault code on the display panel, what does it mean?

If your Glow-Worm boiler is showing the F.28 fault code, it means that ignition has been unsuccessful. Some fault codes on modern boilers are extremely specific. They can highlight not just the problem, but the most obvious solution. That makes fault-finding quicker, and the fix, much cheaper. Unfortunately, the F.28 is specific in terms of the problem, but the solution isn’t as specific.

Anything in your Glow-Worm boiler and heating system that contributes to a successful ignition could be causing the problem. That includes things such as:

Gas pressure to the appliance
Airway blockages, such as the flue or condensate pipe
A faulty, sticking or incorrectly adjusted gas valve
Debris in the burner
Broken spark generator

Your boiler repair company will need to check that the gas pressure to the appliance is sufficient. If it’s not, the burner won’t be supplied with enough gas to ignite, or to continuously burn. The test can be run by checking pressure into the gas meter, out of the gas meter and into the boiler. This will highlight where the exact pressure problem is.

If the issue is pressure to the meter, that’s a job for your utility provider. However, if it’s cold and the problem is pressure out of the meter, it’s likely the regulator has frozen, restricting the flow of gas. If the meter is exposed to the elements, it needs to be boxed in and lagged, to prevent this from happening again.

If the pressure issue is lack of supply to the boiler, they’ll need to inspect the gas main to check it’s up to standard and isn’t blocked.

Likewise, in freezing conditions, the condensate pipe can freeze over. This can be thawed out and lagged, to prevent this from happening again. And, other airways (such as the flue), need to be checked to ensure they’re not clogged up with debris.

Next, they’ll look towards the gas valve. If this is getting no power, incorrectly adjusted or stuck partially closed, the burner won’t be getting sufficient gas, and a flame won’t be produced.

Whereby the gas valve can’t be fixed, your engineer will need to replace it. Typical gas valve replacement costs are in the region of £250-£300.

The burner is another component that needs to be inspected. The smallest piece of debris in the pilot jet will block the flow of gas, and that’s going to lead to no flame being produced or detected.

And finally, your boiler repair company will need to inspect the spark generator. If a spark can’t be generated, a flame is never going to be present.

Is the F.29 fault code on Glow-Worm boilers, the same as the problem causing the F.28 to be displayed?

These two fault codes are different. Although the cause might be similar, there’s a slight difference.

In the case of the F.28 fault code, your boiler has failed to ignite; a flame can’t be produced, or the sensor isn’t detecting a flame.

For the F.29 fault code on Glow-Worm boilers, the problem is flame loss during operation. So, your boiler was able to produce a flame, but it was lost. It’s likely that the problem has suddenly developed, causing the flame to be extinguished.

The causes of the problem are like those of the F.28 fault code. Your emergency boiler repair company is going to be looking out for things such as:

Current gas pressure
Gas valve adjustment
Gas valve operation and faults
Moisture on the electronics
Debris causing a small blockage in the burner.

There are very few DIY fixes for boilers, and there isn’t one to clear the F.29 fault code; you need to speak to a Gas Safe engineer.

They can start by checking the gas pressure to your boiler, working backwards to the pressure leaving the meter, and into the meter.

All being well, they’ll want to take apart your boiler, and check that the gas valve is providing a steady flow of gas. If it’s not, it’s likely that it needs to be adjusted, or it’s completely faulty and needs to be replaced. You should expect to pay £250-300 for a new gas valve to be fitted.

Next, they’ll look at things that could suddenly extinguish a flame, most likely due to a safety boiler lock out. This includes checking for moisture on the electronics. If they find moisture, they’ll not only have to fix the moisture damaged components, but find and fix the leak too.

And finally, they’ll need to check the burner. A sudden blockage in the burner, could extinguish a flame. Although it’s unlikely you’ll need a new heat exchanger, your engineer will need to spend time taking it apart and cleaning it to solve the problem.

Can the F.67 fault code on my Glow-Worm boiler be fixed?

The F.67 fault code on Glow-Worm boilers relates to a problem with the flame signal. Either a flame isn’t present, or the sensors that detect a flame are faulty.

It’s likely your boiler repair company are going to start by checking the flame sensor. If this is defective, even if the flame is present, it won’t be passing on that signal to the PCB. The flame signal will need to be tested for power, and a replacement fitted if necessary.

Likewise, the PCB needs to be tested. If the PCB has an ongoing fault, it might not be receiving the correct signals from the flame sensor, and that’s going to mean that even when a flame is present, the PCB doesn’t think it is.

With the most obvious issues investigated, there are other problems your boiler repair company can look out for. And, that’s because not all fault codes are as specific as they seem.

Your Gas Safe engineer will need to test anything that contributes to your boiler producing and maintaining a flame. That’s going to include things like:

Gas pressure to the meter, out of the meter, and to the boiler
An airway blockage, such as in the flue or condensate pipe
Incorrect gas valve adjustment, or a faulty gas valve
Debris blocking the jet in the burner.

These are all things that help with either the flow of gas to the burner (gas pressure and the gas valve), or help to ensure your boiler is operating in a safe manner (the airways, including the flue and condensate pipe).

Is my boiler dangerous if the F.71 fault code is being displayed, and my boiler locks out?

It’s unlikely that your boiler is dangerous in its locked-out state, especially as this problem doesn’t relate to gas. However, you still need a Gas Safe engineer to carefully inspect your boiler.

The problem that’s causing the F.71 fault code to be displayed, relates to NTC thermistors giving incorrect readings, or no readings at all.

You’ll have a thermistor fitted on the flow and return pipes to your boiler. They monitor resistance in ohms and feedback these readings to the PCB. The PCB then converts them into temperature readings.

The PCB wants to see that the:

Flow pipe isn’t too hot/cold
Return pipe isn’t too hot/cold
The temperature differential between the two isn’t too high

If any of the above are the case, that signifies a problem, and the boiler will lock out.

In the case of the F.71 fault code, it’s likely the NTC thermistors are faulty, or have been fitted incorrectly. Your boiler engineer can quickly check they’re installed on the correct pipes, and that they’re not defective, by testing them with a multi-meter. If they are defective, they’re going to need to be replaced.

If the F.82 fault code is being displayed, is my boiler dangerous?

The F.82 fault code, relates to an issue with gas supply. If the boiler is locked out, it shouldn’t be dangerous. But, it’s important not to try to reset your appliance. There’s a potential leak, and if you do get your boiler working, it could be dangerous to everyone in your property.

Call a Gas Safe registered boiler company and they’ll be able to find the fault.

The most probable cause of the F.82 fault code being displayed is due to the gas valve letting-by. When the PCB is telling it to close, it’s still partially open, most likely due to it being stuck (a widespread problem with old gas valves).

That’s going to result in a flame being present when it shouldn’t be, due to gas entering the burner, when the supply should have been stopped.

Your boiler engineer will need to test the gas valve, to determine if it’s faulty wiring/connections, or a sticking valve that’s causing the problem. And, although gas valves can be freed, it’s unlikely your boiler repair company will want to re-fit an old gas valve, that has already shown signs of being dangerous.

Typically, they’ll want to replace the valve, and that usually costs around £250-300 for most Glow-Worm boilers.

Typically, they’ll want to replace the valve, and that usually costs around £250-300 for most Glow-Worm boilers. If the gas valve isn’t defective, they’ll need to check there isn’t damage to electronics in your boiler, causing intermittent signals to be passed to the gas valve. These checks will include testing the PCB, which controls the gas valve.

Why has my boiler locked out and displayed the F.83 fault code?

If your Glow-Worm boiler has a problem whereby it’s locked out and is now displaying the F.83 fault code, there’s a problem with water not being heated correctly when it fires up.

When your boiler fires up, the NTC thermistors should detect a substantial change in the temperature of flow and return water. In this case, the temperature change is too small, or non-existent.

Your boiler engineer will first, need to check the sensors. There’s one on the burner, flow pipe and return pipe. If they are not giving the PCB the correct readings, the boiler might lock out, even though everything else is working correctly.

If the electronics mentioned above aren’t defective, your boiler engineer needs to check things that might not allow the burner to operate efficiently, as well as checking the supply of gas.

One of the things that can affect the boiler’s ability to circulate water, is low water pressure. This can be topped up via the filling loop. After checking the boiler is set to around 1.3 bar, they can then bleed radiators and towel rails of air.

If the F.83 fault code relates to gas supply, they’ll need to check the operation of the gas valve, as well as ensuring that there’s no debris in the burner. Debris in the burner will stop a steady flow of gas, and a flame will then be intermittent, or non-existent.

How can the F.85 fault code be cleared from my Glow-Worm boiler’s display panel?

The F.85 fault code relates to another NTC thermistor issue. Your boiler is seeing a large differential in flow and return temperatures, getting the same readings from both pipes, or the temperature on one of the two thermistors is too high/too low.

Your boiler repair company will be able to fix this problem, without replacing the boiler. The first thing to check, is that there isn’t a large differential in the flow and return temperature. This can be caused by a:

Blocked pump, or a pump that’s incorrectly adjusted and is on the wrong speed setting
Heating sludge build-up in the system, stopping water from being circulated correctly
Air locks in the pipework, radiators or pump

Next, they’ll want to check that the same reading isn’t being given from the same pipes. If it is, the NTC thermistors have been (incorrectly) fitted on the same pipes or are faulty. They need to be installed correctly, or if they’re faulty, new NTC thermistors will need to be fitted.

My boiler is displaying the F.88 fault code, what does this mean?

The F.88 fault code usually relates to a problem with the supply of gas to your boiler. That’s going to be caused by one of the following issues:

Low gas pressure
A blockage in the flue or condensate pipe, causing the boiler to lock out
A faulty gas valve, or one that’s been incorrectly adjusted
Debris blocking the burner

The most obvious place to start, is the gas valve. These are mechanical components, and over time, they are prone to sticking. If the valve sticks partially closed, when it’s meant to be fully open, the burner in the boiler won’t be provided with sufficient gas. These valves can sometimes be freed. But, if it can’t a replacement is going to be needed.

Another widespread problem is a blockage in an airway. If your Glow-Worm boiler notices that the flue or condensate pipe is blocked, it will lock out as a safety precaution. Your boiler engineer will need to check that both pipes are free from any blockages.

Likewise, a small blockage from debris in the heat exchanger, is going to mean that the burner isn’t provided with sufficient gas. It won’t ignite, or, be able to produce a steady flame. That’s going to result in flame loss, and the boiler locking out.

If all else fails, your boiler engineer will need to check the pressure into your meter, out of your meter, and into your boiler, to see if a lack of physical gas pressure, is what’s causing the issue.

Will I need to replace my boiler if the F.89 fault code is being displayed?

It’s unlikely you’ll need a new boiler if the F.89 fault code is being displayed, if other important boiler components are in good condition. The problem here is with the pump, and in general, it relates to the installation and/or the electronics to and from the pump.

Your boiler engineer will need to check all wiring and connections to and from the pump, re-securing them where necessary.

Sometimes, we find that this problem is due to water damage. That water damage is most likely from the pump itself. If it’s been put under excess pressure (pump speed setting too high, or a heating sludge blockage), it’s likely to blow the seals. That’s going to result in a small leak over all electronics in your boiler, not just the pump’s electronics.

If there’s moisture present in your boiler, you need to get the leak fixed as soon as possible, to avoid any other expensive repair bills.

If your pump is beyond repair, you’ll need a replacement from a top brand like Grundfos. The cost of a replacement pump is likely to be in the region of £250.

Other boiler issues relating to other manufactures

For more boiler issues then please visit the Boiler Problems And Cures page.

24/7 call-out service