Glow-Worm Boiler F.23 Fault Code
The Glow-Worm fault code F.23 relates to a temperature differential between the NTC thermistors that is too great and here we have Q & A or require an engineer for an emergency boiler repair.
The Glow-Worm Boiler Fault Code F.23 Error Common Q & A
Just below, we have a list of common questions relating to the F.23 fault code on the Glow-Worm Boiler.
- What does the F.23 fault code mean on my Glow-Worm boiler?
- What do the NTC thermistors do on my Glow-Worm boiler?
- Why does my boiler lock out if the return NTC thermistor reading is too low?
- What could be the cause of the F.23 fault code being displayed on my Glow-Worm boiler?
- How will my boiler engineer be able to determine if the pump has failed completely?
- How will the boiler repair company know if the pump is using the wrong speed setting?
- How can a pump blockage affect the NTC thermistor readings?
- What causes a blockage in a heating pump?
- Can a central heating sludge blockage be removed?
- Can I protect my heating system from heating sludge?
- How do I get rid of air locks in my heating system?
- Is there anything else that could cause the F.23 fault code to be displayed on my Glow-Worm boiler?
What does the F.23 fault code mean on my Glow-Worm boiler
The F.23 fault code on Glow-Worm Energy boilers, relates to a temperature differential between the NTC thermistors that is too great.
What do the NTC thermistors do on my Glow-Worm boiler
Your boiler is controlled by the printed circuit board (PCB). It’s this component that gives and receives signals to and from all other electrical components in the boiler; that includes signals from the NTC thermistors.
There’s one located on the flow pipe (hot water that’s leaving the boiler), and another on the return pipe (cooler water that’s travelled around the heating system and is ready to be re-heated).
Naturally, water will lose temperature as it travels around copper pipework, and radiators. But, it shouldn’t lose masses of temperature. When it does, that indicates a problem. The boiler notices that the reading on the return NTC thermistor is too low and locks out the boiler.
Why does my boiler lock out if the return NTC thermistor reading is too low
There’s one of two reasons a boiler will lock out:
- There’s a chance the boiler is dangerous
- Continued operation would damage expensive parts.
In this case, it’s the latter. The boiler sees a mechanical issue that needs to be fixed. Continued operation would potentially damage important and expensive parts. By locking out and fixing the problem now, it will save much larger boiler repair bills later.
What could be the cause of the F.23 fault code being displayed on my Glow-Worm boiler
Usually, the main cause of the F.23 fault code being displayed is something that is hampering the boiler’s ability to circulate water.
For instance:
- Pump failure
- Incorrect pump speed
- Pump blockage
- Air locks
However, if these can all be ruled out, the next stage is to asses the NTC thermistors. The components could be faulty, or fitted on the wrong pipes (although, the latter is extremely rare).
How will my boiler engineer be able to determine if the pump has failed completely
As the pump is an electrical component, your boiler repair company will be able to test it using a multi-meter. They’ll be checking that the pump, as well as wires and connections, are all getting power. If the pump can then be isolated as the problem, it will need to be replaced.
Usually, emergency boiler repair companies will swap an old pump, with one from a leading brand such as Grundfos. For a Glow-Worm boiler, we’d expect the cost of a replacement pump to be in the region of £250.
How will the boiler repair company know if the pump is using the wrong speed setting
Most newer pumps will have three speed settings. If you live in a large property and the pump is set on the slowest speed setting, it’s unlikely that’s going to be powerful enough for your heating system.
Water travels around the system slowly, losing lots of temperature in the process. Your boiler engineer can check the size of your heating run and determine which speed setting is most suitable.
Although the installer of the boiler should have set the speed setting correctly, there’s a chance the property layout and heating system, might have changed since.
For instance, if you’ve added radiators or towel rails (in an extension for example), that’s extra water that needs to be pump around the heating system. The original flow setting won’t be high enough.
How can a pump blockage affect the NTC thermistor readings
As we’ve already mentioned, any restriction in flow, is going to mean that temperature on the return pipe is affected.
If the pump is even partially blocked, water flow is going to be limited. Water travels slowly, cools quickly and when it returns, it’s well below temperature. A blockage isn’t just putting the pump under strain, it puts the heat exchanger under lots of strain too.
What causes a blockage in a heating pump
The most probable cause of a blockage in a heating pump, is central heating sludge build-up.
Central heating sludge is essentially, rust from the inside of radiators, towel rails and pipework. That’s mixed in with limescale to create dirty heating water.
This sludge can find its way just about anywhere. You might have noticed radiators getting hot at the top, but they stay cold at the bottom. That’s because heating sludge has settled at the bottom of the radiator. Water finds the path of least resistance and therefore, flows straight past wherever the sludge has settled.
Whilst most of central heating sludge breaks down, not all of it does. You’ll find that small pieces of rust lodge themselves in expensive boiler components, including the pump. And as we know, that’s going to restrict the pump’s ability to circulate water.
But, it’s not just circulation that’s affected. The partial blockage puts excess strain on the pump’s shaft, bearings and seals. This is going to mean that the pump fails years before it should.
Can a central heating sludge blockage be removed
You may have heard of a process called power flushing. Now, this high pressure internal clean, gets rid of most heating sludge. The problem is, it’s old heating systems that are most likely to need cleaning, but they’re also the ones that are most prone to leaks. This high pressure clean is likely to cause leaks.
So, a hot flush is preferred. Instead of using additional pressure, the boiler engineer will add chemicals and run the boiler at maximum power to break down any lose pieces of sludge. This can then be flushed clear of the heating system. It’s nearly as effective as a power flush and is a lot less likely to cause leaks (and therefore, less likely to add to your repair bill).
Can I protect my heating system from heating sludge
Heating sludge is a big problem in boilers. So, don’t think that with a quick clean, it won’t happen again. The cost of protecting your boiler, is a lot less than fixing it.
The first stage of protection has been mentioned above; a hot flush.
Once the system has been flushed, make sure your engineer doses it with central heating inhibitor. This chemical will continuously break down the sludge into pieces small enough, so they won’t block components such as the heat exchanger and pump.
Next, ask to get a magnetic system filter fitted. Top brands include the likes of BoilerMag, Fernox and Magnaclean. These filters catch the sludge particles that the inhibitor breaks down. The filter can then be cleaned out with an annual boiler service.
Finally, there is an additional preventative measure for those in hard water areas. These areas are prone to having problems with limescale. And, there are filters that can be fitted, in addition to the magnetic filter mentioned above, called limescale reducers.
How do I get rid of air locks in my heating system
Air locks act like blockages. So, they need to be removed. You can bleed air from your heating system using a radiator bleed key. Slowly open the bleed valve on each radiator, and you’ll a hissing noise.
The hissing will eventually stop, replaced by a slight dribble of water; that means all air has been bled. Rinse and repeat for all towel rails and radiators in the property.
Is there anything else that could cause the F.23 fault code to be displayed on my Glow-Worm boiler
If your boiler engineer has ruled out a blockage, faulty pump, or air locks, they’ll need to look at the PCB. It’s likely the problem could be electrical. As the PCB is the component that controls all electrical components, this is the best place to start.
Like the boiler’s pump, the PCB can be checked using a multi-meter. Unfortunately, if it is the PCB that’s the problem, it could cost upwards of £450 to fix.
Other Glow Worm boiler issues
For more boiler issues regarding the Glow Worm then please visit the Glow Worm Boiler Problems And Cures page.