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Glow-Worm Boiler F9 Fault Code

The Glow-Worm fault code F9 relates to the water pressure sensor and here we have Q & A or require an engineer for an emergency boiler repair.


The Glow-Worm Boiler Fault Code F9 Error Common Q & A

Just below, we have a list of common questions relating to the F9 fault code on the Glow-Worm Boiler.

Glow-Worm boiler error code F9
  • What does the F9 fault code mean on my Glow-Worm boiler?
  • What is the most likely cause of the F9 fault code being displayed on my Glow-Worm boiler?
  • Why would the pressure sensor break?
  • Could other electrical faults cause the F9 fault code to be displayed on my Glow-Worm boiler?
  • My boiler engineer thinks the PCB on my boiler is the problem, how much is this going to cost to replace?
  • Will resetting my boiler clear the F9 fault code?
  • Could a leak have caused my boiler to display the F9 fault code?
  • How are leaks, water pressure and the F9 fault code connected?
  • Can I fix the F9 fault code on a DIY basis?
  • I’ve put too much water (and pressure) in my boiler, is it dangerous?
  • My pressure on my boiler has been dropping, is there a DIY fix for the F9 fault code?
  • What else should my boiler engineer be looking out for, to clear the F9 fault code?

What does the F9 fault code mean on my Glow-Worm boiler

If your Glow-Worm boiler develops a problem, the printed circuit board (PCB) is going to find the most relevant fault code and show it on the display panel; F9 in this case.

The F9 fault code on Glow-Worm boilers relates to a water pressure sensor. The sensor is detecting that water pressure has dropped to a point whereby the boiler shouldn’t be operational. That means as well as the fault code being displayed, the boiler will lock out.

What is the most likely cause of the F9 fault code being displayed on my Glow-Worm boiler

The PCB is the part in your boiler that gives and receives signals to all electronic parts. In this case, it’s getting the signal that the pressure on the boiler is too low.

There are two possible scenarios:

  • The water pressure sensor is faulty
  • The water pressure is too low.

So, they’ll start by checking the water pressure sensor. It’s not uncommon for these to fail. However, the PCB’s fault code system isn’t always perfect. And, that means that there’s a high possibility that there’s something that’s led to the boiler losing pressure, and that’s what’s triggered the F9 fault code to be displayed.

Why would the pressure sensor break

Old age is a major killer of boilers. And, it’s likely that internal boiler vibrations have caused connections and wires to become loose or damaged. If they’re not in extremely poor condition, on some occasions, they can be repaired.

Could other electrical faults cause the F9 fault code to be displayed on my Glow-Worm boiler

Electrical faults aren’t always what they seem. After checking the water pressure sensor for faults, your Gas Safe engineer will want to do a quick visual inspection of the internal electronics. Everything from boiler vibrations to water damage, could cause a range of electronic components to fail.

What they’ll be focusing on most, is the boiler’s PCB. It’s this component that doesn’t just control components, but decides which is the most relevant fault code to display when there’s a problem.

Visually checking and then testing the PCB using a multi-meter will help to determine if there are any faults here.

My boiler engineer thinks the PCB on my boiler is the problem, how much is this going to cost to replace

Your Gas Safe boiler repair company will need to discount all other components on your boiler as being the problem, before blaming the PCB, as this is one of the most expensive parts to replace. You should expect to pay anywhere between £400-500 for a replacement, depending on the type of boiler that you have.

And, with repairs that are this high in cost, we’d suggest giving your boiler a thorough health check. A new boiler for small properties could be as little as £1,800. So, if the PCB and even one other component is in poor condition, it might be worth investing in a new boiler, rather than one that is deteriorating rapidly.

Will resetting my boiler clear the F9 fault code

Resetting your boiler isn’t going to fix the problem. You might temporarily trick the boiler into thinking that the problem is fixed. That’s going to mean that if there is a problem with low water pressure, many parts in your boiler are going to be put under unnecessary strain. And, that’s only going to lead to more expensive repair bills. It’s likely after a few minutes, the boiler will lock out again anyway.

If you see the F9 fault code being displayed, don’t try and reset your boiler. The problem needs to be found and fixed before the reset function is used. And, we’d recommend calling a Gas Safe boiler repair company to come and do this on your behalf.

Could a leak have caused my boiler to display the F9 fault code

There’s every possibility that the F9 fault code stems from a leak. Leaks and low water pressure are both common problems on modern boilers, and the two problems are connected.

The amount of pressure in your system, is based on the amount of water it contains. The more water contained in your central heating system, the higher the pressure.

These leaks can occur just about anywhere. They can come from towel rails, copper pipework, but they can also come from inside the boiler. When they come from inside the boiler, they can cause an immense amount of damage to electrical components.

How are leaks, water pressure and the F9 fault code connected

Your boiler needs a certain amount of pressure to operate. Typically, a Gas Safe engineer will set your boiler’s pressure to 1.3 bar. Most manufacturers then build-in a failsafe. Once the boiler rises above 3 bar, or drops below 0.5 bar, the boiler will stop working (lock out).

In this case, if the pressure sensor isn’t faulty, it’s likely your boiler has dropped below 0.5 bar. And, the most likely cause of the reduction in pressure, is going to be due to there being a leak in the central heating system.

Can I fix the F9 fault code on a DIY basis

There are few fault codes that can be fixed on a DIY basis. If your boiler isn’t leaking and for whatever reason, is set to below 0.5 bar, then this is a fault code that can be fixed on a DIY basis.

Each boiler has a filling loop. This is a small braided hose beneath the boiler’s casing, with a valve on it. Opening this valve allows water to enter the system, and that’s going to boost the pressure. As we’ve mentioned, 1.3 bar of pressure is the optimum for most boilers, but always check your owner’s manual.

I’ve put too much water (and pressure) in my boiler, is it dangerous

If you’ve left the filling loop open for too long, you’ll have overfilled the central heating system with water, and put in too much pressure. That’s going to put excess pressure on a range of boiler components, the pump for instance.

You should drain water (therefore, removing pressure), from the boiler as soon as possible. You can do this in two different ways.

First, you can find the drain cock. Using a small hose, you can drain water from the heating system until it reaches the desired 1.3 bar of pressure.

Secondly, you can bleed the radiators using a bleed key. Slowly open these valves and ensure that walls and floors are protected, as opening them too fast can lead to a small spray.

My pressure on my boiler has been dropping, is there a DIY fix for the F9 fault code

As we’ve mentioned, you shouldn’t top up your boiler’s pressure with the filling loop, if your boiler is losing pressure. If it is losing pressure, there’s a good chance that this is due to a leak in the heating system.

Whether the leak is in the boiler, pipework, or radiators, you need to find the leak first, before adding pressure to your system. If you don’t, you’ll be speeding up the process of water damage. And, that’s because the more pressure you add to a central heating system, the faster it’s going to leak water.

What else should my boiler engineer be looking out for, to clear the F9 fault code

It’s extremely rare, but one problem we’ve found, is a pump proving issue. And, that’s going to be a miscommunication between the pump, and the water pressure sensor. The water pressure sensor needs to see a small rise in pressure as the pump kicks into life (usually, within the first 10 seconds). If it doesn’t then it’s going to assume that there’s a problem and lock out the boiler.

This might be a wiring issue (this can be tested using a multi-meter and completing a visual inspection). But on some occasions, there is a fault with the pump, which is usually a fault that reduces its ability to circulate water. That includes things like air locks, and central heating sludge build-up. Your boiler engineer will need to fault-find the pump, fix it, and reset the boiler to clear the fault code.

Other Glow Worm boiler issues

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