Glow-worm Green LED Off Fault Code: Causes, Fixes & Repair Costs
What does the Glow-worm Green LED Off fault code mean?
On Glow-Worm boilers that use LED status indicators rather than a digital display — most notably the Betacom range — the green LED being completely off means the boiler is receiving no electrical power at all. Without a 230 V mains supply the boiler cannot start, so there will be no heat, no hot water, and no other indicator lights active. The very first thing to establish is whether electricity is reaching the unit, starting at your consumer unit and working forward to the boiler itself.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Tripped circuit breaker or blown fuse at the consumer unit Common
A tripped breaker or blown fuse on the circuit that feeds the boiler is the most frequent reason the green LED goes dark. Check your consumer unit for any tripped switches — usually labelled 'boiler' or 'heating' — and look for a blown fuse if your consumer unit uses fuse wire rather than MCBs.
- Blown internal boiler fuse Common
Glow-Worm boilers typically have a 3 A fuse on the PCB or in the wiring. A power surge or minor component fault can blow this fuse silently, cutting all power to the board and extinguishing the green LED entirely. This fuse is inside the boiler casing.
- Loss of mains supply to the boiler Sometimes
The spur socket or fused spur that feeds the boiler may have developed a fault, or the isolating switch beside the boiler may have been accidentally turned off. Confirming whether 230 V is present at the boiler's terminal block is a straightforward electrical check for an engineer.
- Damaged or loose wiring Sometimes
A wire that has come loose at a terminal, been pinched in the boiler casing during a previous service, or suffered insulation damage can interrupt the power supply to the PCB, producing the same dead-boiler symptom as a complete power failure.
- Faulty PCB (printed circuit board) Rare
If mains power is confirmed at the boiler and all fuses are intact yet there are still no signs of life, the main PCB itself may have failed. The PCB is the brain of the boiler; a dead board will leave every indicator unlit. An engineer will test the board before condemning it, as a poor connection from a wiring harness can mimic a failed board.
How to fix it
- Check your consumer unit for a tripped breaker or blown fuse DIY safe
Go to your consumer unit (fuse box) and look for any switch that has tripped to the middle or off position. If you find one labelled 'boiler' or 'heating', reset it by pushing it fully off then back on. If it trips immediately again, do not reset it a second time — that points to an electrical fault requiring a qualified electrician or Gas Safe engineer.
- Check the boiler's isolating switch and fused spur DIY safe
Locate the fused spur or double-pole isolating switch mounted near the boiler (often on the wall beside it). Make sure it is switched on. Some fused spurs contain a 3 A or 13 A cartridge fuse — if yours is accessible and you are comfortable doing so, check the fuse is intact and replace it with a correctly rated cartridge if blown.
- Switch the boiler off at the mains, wait a few minutes, then switch it back on DIY safe
Turn the boiler off using its isolating switch, leave it for two to three minutes to allow any residual charge to clear, then switch it on again. This is the equivalent of a hard reset and can resolve transient power glitches. Do not repeat this more than two or three times if the LED stays off.
- Check for any obvious wiring issues visible without opening the casing DIY safe
Without removing any boiler panels, inspect the external cable running from the wall to the boiler for visible damage such as scorch marks, cuts, or kinks. Do not open the boiler casing or touch any internal wiring yourself.
- Have a Gas Safe engineer inspect and test the internal fuse and wiring Gas Safe engineer
If the green LED remains off after the checks above, an engineer needs to open the casing and use a multimeter to confirm 230 V is reaching the PCB, test the onboard fuse, and check for loose or damaged wiring within the boiler. This work involves live electrical components inside the boiler and must not be attempted by a homeowner.
- Have a Gas Safe engineer test and, if necessary, replace the PCB Gas Safe engineer
If power and fusing are confirmed to be fine, the engineer will test the PCB to determine whether it has failed. Before replacing the board they will typically check the wiring harness connections, as a poor connection can look identical to a dead PCB. PCB replacement is specialist work and must only be carried out by a qualified engineer.
Parts you may need
- Boiler internal fuse (3 A cartridge) · from £3
- Fused spur switch (13 A) · from £18
- PCB (Betacom/Glow-Worm main circuit board) · from £220
- Wiring harness · from £55
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £80–£350, depending on the underlying cause.
Frequently asked questions
Why is the green LED off on my Glow-Worm Betacom boiler?
The green LED being off simply means no electrical power is reaching the boiler. The most common culprits are a tripped circuit breaker at the consumer unit, a blown fuse in the fused spur beside the boiler, or a blown internal fuse on the PCB. Start by checking your fuse box; if everything looks normal there, you will need a Gas Safe engineer to test the electrics inside the boiler.
Can I fix a Glow-Worm with no power myself?
A few basic checks are safe for a homeowner: resetting a tripped breaker, replacing the fuse in a fused spur switch, and performing a hard reset by switching the isolator off and on. Anything beyond that — including opening the boiler casing, testing wiring, or replacing the PCB — must be done by a Gas Safe registered engineer because it involves live electrical components inside a gas appliance.
How much does a Glow-Worm PCB replacement cost in the UK?
A PCB replacement typically costs between £250 and £400 including parts and labour, depending on the specific board required and your location. This sits at the higher end of what most people pay for this fault. If the problem turns out to be just a blown fuse or a loose wire, the repair can cost as little as £80 to £120 for a call-out and minor fix.
My circuit breaker keeps tripping when I reset it — what should I do?
A breaker that trips repeatedly is telling you there is an active electrical fault on the circuit — do not keep resetting it. Turn the boiler isolator off to disconnect the appliance and contact a Gas Safe registered engineer (or a qualified electrician if you need the circuit itself checked) as soon as possible. Repeated tripping can indicate a short circuit in the boiler wiring or a failing component that needs professional diagnosis.