Glow-Worm Boiler F26 Fault Code
The Glow-Worm fault code F26 relates to poor circulation and here we have Q & A or require an engineer for an emergency boiler repair.
The Glow-Worm Boiler Fault Code F26 Error Common Q & A
Just below, we have a list of common questions relating to the F26 fault code on the Glow-Worm Boiler.
- What does the F26 fault code mean on my Glow-Worm boiler?
- Can I fix the F26 fault code on a DIY basis?
- What causes the F26 fault code to be displayed?
- How can my heating company check the NTC thermistor’s resistance reading?
- Why would connections and wiring be causing the F26 fault code to be displayed on my boiler?
- How can the pump lead to the F26 fault code being displayed?
- The heating company is also suggesting fitting a limescale filter, should I get one?
- My boiler engineer thinks I need a new pump, is this right, and how much will it cost?
- Where do air locks occur, and how can they be removed?
- How do I increase the pressure on my boiler?
What does the F26 fault code mean on my Glow-Worm boiler
If your boiler is showing the F26 fault code, the problem is poor circulation.
Each boiler has a flow and return. The flow is water leaving the boiler, after it has been heating. It is pumped around the heating system, and after travelling through all radiators and pipework, will re-enter the boiler via the return pipe.
There’s a sensor on the return pipe called a thermistor. This monitors water temperature in resistance. The higher the temperature is, the lower the resistance reading. It’s the printed circuit board (PCB) that translates this resistance reading to a temperature, and then decides whether it’s correct.
In this case, it’s likely the thermistor has noticed a low return temperature when compared with the flow temperature; the differential is too high. And that’s because something is hindering the circulation of water in your boiler.
The PCB determines when there’s a problem, and then shows a fault code to signal that it needs to be fixed. In extreme circumstances, it might lock out. This is to stop any components that are suffering from damage, from getting damaged further.
Can I fix the F26 fault code on a DIY basis
Unfortunately, the F26 fault code isn’t one that can be fixed on a DIY basis. You’ll need a boiler repair company to come and inspect your appliance. Once they’ve diagnosed and fixed the fault, they’ll be able to reset your boiler. A reset will clear the F26 fault code from the display panel.
What causes the F26 fault code to be displayed
Your central heating engineer will need to check various components that affect temperature readings and circulations, and not just in your boiler, but throughout your central heating system. They’ll be looking for:
- Correct resistance readings from the heating return NTC thermistor
- Connections and wiring between the NTC thermistor and the PCB
- The pump, to ensure its circulating water correctly
- Air locks
- Blockages
The reason your heating engineer will start with the NTC thermistors, is because if they’re faulty, they could be indicating incorrect temperature readings, leading to the PCB thinking there is a circulation fault when there isn’t.
How can my heating company check the NTC thermistor’s resistance reading
As we’ve mentioned, the NTC thermistor helps the PCB determine what temperature the water in the heating system is currently at. This component needs to be tested, and the right tool to test it, is a multi-meter.
When at 20C, they’d expect to see a resistance reading of around 12K ohms. If it’s above or below this, or no resistance reading is found, it’s likely that the NTC thermistor on the heating return has failed. In this case, a new NTC thermistor will need to be fitted.
Why would connections and wiring be causing the F26 fault code to be displayed on my boiler
Electrical components are extremely fragile. Even the slightest of damage to connections or wiring, could cause a component to fail.
And, the same goes for water damage. Many old boilers eventually fail due to water damage, which can come in several forms. For instance, a heating pump with leaking seals, can provide enough moisture to damage components and their wiring/connections.
Your heating company can start by doing a visual inspection, looking for any burnt out connections, or obvious damage to wiring.
In many cases, damage comes in the form of loose connections, and these connections can simply be secured. But, if damage has occurred, it needs to be repaired for the PCB to effectively communicate with the NTC thermistor on the central heating return pipe.
How can the pump lead to the F26 fault code being displayed
There isn’t just an NTC thermistor on the return pipe, but on the flow also. So, when water leaves the boiler, the temperature is logged by the PCB. And likewise, when it re-enters the boiler via the return pipe.
If there is any kind of circulation restriction, the temperature of the flow and return water is going to be affected. The time taken for water to travel around the heating system is more than usual, and that’s going to lead to it losing more temperature than it should.
Ultimately, that means that the differential between the two thermistors readings is too high, and the boiler locks out.
Your heating repair company will need to check that the pump is on the correct speed setting. On most modern pumps, there are three speed settings available. If your pump is set on the slowest speed setting and you have a large heating system, it might need to be switched to a more powerful setting.
Next, they’ll need to check there aren’t any blockages. These blockages can be a combination of air and heating sludge.
The air can be removed using the bleed screw, and the heating sludge can be removed manually. However, to ensure that heating sludge doesn’t return, they’ll need to flush the heating system out, dose it with inhibitor, and fit a boiler filter to catch and debris, long-term.
The heating company is also suggesting fitting a limescale filter, should I get one
Prevention is always better than cure. Limescale is a widespread problem in hard water areas. And, it won’t just lead to a blockage in the pump, but the heat exchanger too; that’s an expensive part to replace.
A limescale filter will reduce the chance of a pump getting blocked, as well as other expensive components, not to mention your boiler operating more efficiently. So, if you’re in a hard water area, a limescale filter will be a good investment. Top brands include Magna Clean, Boiler Mag, Fernox, Sentinel and Scale Master.
My boiler engineer thinks I need a new pump, is this right, and how much will it cost
Not all faults relating to pumps and the F26 fault code are simple to fix. If your pump is working sporadically because of long-term water damage to electrics or has worn bearings and weak/blown seals, it might be worth considering a replacement.
Typically, we’d expect a replacement pump to cost around £250. That’s a top-quality pump from a manufacturer such as Grundfos, and includes the price of labour.
Where do air locks occur, and how can they be removed
We’ve already mentioned above air locks can occur in pumps, and can be removed using the bleed screw. But, they are more commonly found in towel rails and radiators. And, they can be removed on a DIY basis.
Before removing air locks, check to see what your boiler’s pressure is; it should be around 1.3 bar.
Now, choose a radiator, and protect walls and floors, and make sure you have a container to hand, to catch any water that is released from the radiator.
You can open the bleed screw using a radiator bleed key. What you’ll hear, is a hissing noise; this is air being released from the system. Once all the air has been released, the hissing noise will be replaced with a dribble of water. That signifies that air has been removed from that radiator.
After bleeding radiators and towel rails, you’ll need to head over to the boiler. Typically, after releasing air from the system, you’ll have also removed pressure. If the pressure has dropped below 1.3 bar, you’ll need to top it up.
How do I increase the pressure on my boiler
Locate the filling loop, which is a small braided hose with a valve on it. Opening this valve is going to allow water into the system, and that means pressure will increase on your boiler’s pressure gauge. Again, we are aiming for 1.3 bar.
If you add too much pressure, you can release it by bleeding the radiator as you did earlier. But this time, you’ll need to allow water to escape, and have someone checking the pressure gauge, to let you know when the gauge is set to 1.3 bar.
Other Glow Worm boiler issues
For more boiler issues regarding the Glow Worm then please visit the Glow Worm Boiler Problems And Cures page.