Glow-worm F1 Fault Code Explained

If your Glow-worm boiler has flashed up an F1 code and gone cold, you're probably standing in a chilly kitchen wondering whether it's a quick fix or something more serious. The good news is that the F1 fault code on Glow-worm boilers is one of the more common ones, and it usually comes down to either low water pressure or a fault with the printed circuit board (PCB).

What does F1 actually mean

On most Glow-worm models, including the popular Betacom and Ultracom ranges, F1 signals a water pressure issue detected by the boiler's internal pressure sensor. It can also appear if the sensor itself has failed, or in rarer cases if there's a wiring fault on the PCB. Because the same code can point to a few different root causes, it's worth checking the simple things first before assuming the worst.

Common causes of the F1 code

• Low system pressure, often below 1 bar on the boiler's gauge
• A recent radiator bleed that let air (and pressure) out of the system, see our bleed a radiator guide if you've had one hissing
• A faulty or sticking pressure relief valve
• A failed pressure sensor sending incorrect readings to the PCB
• Loose or damaged wiring inside the boiler casing

If your pressure keeps dropping repeatedly rather than being a one-off, it's likely a leak somewhere in the system rather than the sensor itself. Our pressure guide walks through how to spot and fix that.

How to try a reset

Most Glow-worm boilers let you top up the pressure using the filling loop, then reset the boiler using the button on the front panel. Check the pressure gauge is sitting between 1 and 1.5 bar when the heating is off, top up gently if it's low, then hold the reset button for a few seconds.

If the code clears and stays clear, you're likely fine. If F1 comes straight back, or the pressure won't hold, it's time to call in a professional rather than keep resetting it. Repeated resets without fixing the underlying cause can mask a bigger problem and, in rare cases, isn't safe.

When to call an engineer

Any fault involving the PCB or persistent pressure loss should be looked at by a Gas Safe registered engineer. You can check any engineer's registration on the Gas Safe Register before they start work, which is worth doing whoever you use. Glow-worm's own support pages, alongside general guidance from the Energy Saving Trust on boiler maintenance, both recommend not attempting internal repairs yourself.

Is it time for a new boiler

If your Glow-worm is older and F1 keeps recurring alongside other faults, it might be cheaper long term to replace than repair. Our signs you need a new boiler article covers the warning signs, and our new boiler cost guide gives realistic UK Midlands pricing so you know what to expect before you commit either way.

Regular servicing also catches pressure and sensor issues early, long before they become a cold house on a Sunday morning.

If resetting hasn't worked and you need someone out quickly, book an emergency callout and we'll match you with a Gas Safe engineer covering your area.