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Glow-Worm Boiler F19 Fault Code

The Glow-Worm fault code F19 relates to a central heating NTC thermistor being unplugged and here we have Q & A or require an engineer for an emergency boiler repair.


The Glow-Worm Boiler Fault Code F19 Error Common Q & A

Just below, we have a list of common questions relating to the F19 fault code on the Glow-Worm Boiler.

Glow-Worm boiler error code F19
  • What does the F19 fault code mean on my Glow-Worm boiler?
  • What does the heating thermistor do on my boiler?
  • Can I fix the F19 fault code on a DIY basis by resetting my boiler?
  • What’s the most likely cause of the F19 fault code being displayed on my Glow-Worm boiler?
  • Can this problem be easily fixed?
  • If the thermistor isn’t the problem, what else will my boiler repair company be looking for?
  • Will my boiler repair company be able to fix the PCB, if it’s at fault?
  • If I need a new PCB on my Glow-Worm boiler, how much is it likely to cost?
  • What can cause a PCB to fail?
  • My boiler repair company thinks the best option is a new boiler, is that right?

What does the F19 fault code mean on my Glow-Worm boiler

The F19 fault code on your Glow-Worm boiler relates to a central heating NTC thermistor being unplugged.

When your boiler’s printed circuit board (PCB) recognises there is a problem like this, it doesn’t just display a fault code, it is likely to lock out.

The reason your boiler locks out in this case, is it’s not able to monitor the temperature of water in the central heating system.

If it can’t monitor the temperature of water, it can’t recognise if there are further problems. And, problems that relate to water temperature being incorrect, are likely to mean that expensive damage is caused to a range of internal boiler components.

What does the heating thermistor do on my boiler

Your boiler has a range of sensors. The job of these sensors is to monitor pressures and temperatures, and then feed back these signals to the PCB. Once the PCB receives these signals, it can understand if there’s a problem and if so, what the problem is likely to be. And, the NTC thermistor on your central heating, is one of these sensors.

The NTC thermistors on boilers monitor resistance, and send signals in ohms. The higher a temperature is, the lower the resistance reading is going to be. Given these resistance readings, the PCB can convert this into a temperature.

As an example, when you switch on your central heating, your PCB expects to see a reading that correlates to an increase in temperature, from the NTC thermistor. If it doesn’t, or that reading converts to a temperature that’s too high, that signifies that there’s a problem.

Can I fix the F19 fault code on a DIY basis by resetting my boiler

There are only a few faults on boilers that can be fixed on a DIY basis. For instance, an error that requires boiler pressure to be topped up.

The F19 isn’t one of these fault codes. Resetting a boiler won’t fix the problem at hand. The reset function on your boiler should only be used once the problem has been fixed. Otherwise, there’s a chance that continued operation of the boiler could result in further damage, and expensive repair bills.

You should always consult an emergency boiler repair company. They’ll have qualified Gas Safe engineers that are trained to work on gas boilers.

What’s the most likely cause of the F19 fault code being displayed on my Glow-Worm boiler

The most likely cause of the F19 fault code, is the NTC thermistor isn’t fitted correctly, or has become disconnected. If this is the case, no reading is going to be present. As the PCB doesn’t know whether the boiler is working within operating tolerances, the best thing for it to do, is lock out, until the boiler has been inspected.

Can this problem be easily fixed

If the NTC thermistor on the central heating system has become unplugged, it can be plugged back in to fix the problem. Your boiler may still show the F19 fault code, even after the thermistor has been plugged back in. The boiler will need to reset, for the fault code to be cleared.

But, if the problem persists, there might be a more serious fault. The most obvious place to start would be with the thermistor. As we’ve mentioned, it should be showing a resistance reading. If the part is faulty, the resistance reading might not be present, or may be incorrect.

Your boiler repair company will be able to test the NTC thermistor on your central heating using a multi-meter. They’ll expect to see a reading of around 12,000 ohms when at 20C. If they don’t, it’s likely that the thermistor needs to be replaced.

If the thermistor isn’t the problem, what else will my boiler repair company be looking for

If the thermistor isn’t the problem, the next place to look, is the boiler’s PCB. The boiler’s PCB gives and receives signals to all electronic components, and that includes the NTC thermistors. Even a small electrical fault within the PCB, is going to mean that the boiler doesn’t work.

In fact, it’s the boiler’s PCB that determines which fault codes should be displayed and when. It stands to reason that if the PCB is at fault, the error code being displayed could be incorrect too.

So, like they did with the thermistor, your boiler engineer will need to check the PCB for power. This means checking the PCB, but also, any connections and wiring to it. Even one faulty connection could lead to the PCB giving and receiving signals on an intermittent basis.

Will my boiler repair company be able to fix the PCB, if it’s at fault

If the problems with your PCB are minor, they can be fixed. For example, your repair company can secure connections, and replace small sections of wiring. However, if the damage is due to excessive vibrations, or even a boiler leak, it might be that the PCB needs replacing, not the thermistor.

If I need a new PCB on my Glow-Worm boiler, how much is it likely to cost

Your boiler repair company will want to be 100% sure that the PCB is to blame, as it’s the most expensive part in a boiler to replace.

Depending on the exact model of Glow-Worm boiler that you own, the replacement costs could be in the region of £400-500.

Typically, you’d expect the job to be completed within one day. However, these aren’t spare parts that repair companies have on their vans. So, they’ll need to order in a PCB from a merchant. It could be 2-3 days before your boiler is fixed.

What can cause a PCB to fail

Whilst old age is a killer of boilers, it’s not always to blame. If your boiler engineer is seeing multiple burnt out connections, there’s a chance that water damage is the culprit. Water damage can come from multiple sources, including the pump and heat exchanger.

Unfortunately, as older appliance’s electrical components aren’t particularly well sealed, even the slightest sign of moisture is enough to cause major damage.

If you’ve noticed pooling beneath your boiler, or your engineer suspects water damage, that needs to be fixed, alongside the PCB. If it’s not, the same problem is going to occur.

Typically, the fix is simple. If the heat exchanger is leaking, it’s going to be due to a crack, possibly caused by limescale. The heat exchanger, like the PCB, isn’t a cheap part to replace. You should expect to pay around £400 for a new heat exchanger.

Another part worth looking at, is the pump. A pump can leak via the seals. This could be due to old age and the seals degrading, excess pressure due to the incorrect speed setting being used, or sludge build-up.

Your engineer will need to clear any heating sludge, ensure the pump is on the right speed setting, and replace the seals to stop the leak.

My boiler repair company thinks the best option is a new boiler, is that right

If you have an old boiler that’s out of warranty and a repair bill of £400+, it’s worth considering getting quotes for a new boiler. The PCB is an extremely fragile part, so it’s usually one of the first to break. This could be a sign that other parts are about to follow.

If in doubt, get your boiler repair company to inspect other expensive parts and determine their condition.

This will include the heat exchanger, gas valve, fan and pump. If it’s likely they’ll need replacing soon, a newer boiler could be a better option. And, that’s not just because you’ll save on repair costs. Old boilers can be as low as 60% efficient, and many new boilers are over 89% efficient, meaning you’ll save plenty on your energy bills too.

Other Glow Worm boiler issues

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