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Laser powers on and moves, but won't fire
The head tracks the whole job perfectly and the material comes out untouched. This is a different fault from not cutting all the way through — there, the beam is weak; here, there is no beam at all. That distinction matters, because it rules out most settings causes immediately and points at a much shorter list.
Price a job in your browser →Work the list in this order
It is ordered by how common and how cheap each cause is. Do not start by suspecting the tube — it is the most expensive answer and one of the least likely.
1. Is the software actually asking for power?
Surprisingly often, nothing is wrong with the machine.
- Layer set to a non-output mode. In LightBurn, check the layer is not set to Tool (or that Output is not switched off). A Tool layer moves the head and deliberately never fires.
- Power set to zero, or min power at zero. On a CO2 with min/max power, a max of 60% with a min of 0% can produce almost nothing on small geometry, because the machine ramps power with speed.
- Wrong device or profile selected, so the controller receives commands it ignores.
- “Frame” vs “Start”. Framing intentionally does not fire. Make sure the job really was started.
2. Interlocks and lid switches
Nearly every enclosed machine refuses to fire with the lid open, and the switch that senses this is a common failure point. Signs: the machine runs the job normally, no error appears, but there is no beam. Check the lid magnet or microswitch is aligned and clean; on many machines you can hear the switch click as the lid closes.
3. CO2 only: water flow and temperature protection
A CO2 tube is protected by a flow switch and often a temperature cut-out. If either is unhappy the controller will run the job and simply never enable the tube.
- Is the pump actually running, and is water visibly moving through the tube?
- Air lock in the tube — tilt the machine or the tube slightly to release trapped air.
- Flow switch stuck or failed — a classic cause of “it worked yesterday”.
- Water too warm (over roughly 25 °C) tripping the cut-out, or so cold it has condensed.
4. Do a controlled test fire
Most CO2 machines have a physical Pulse or Test button. With the lid closed and a scrap of masking tape or card at the focal point, pulse briefly at around 15–20% power.
- A mark appears: the tube, PSU and optics are alive. The fault is in the job, the layer settings or the controller path — go back to step 1.
- Nothing at all: the fault is in the power chain. Continue to step 5.
- If your machine has an mA meter, watch it during the pulse. Zero mA means the tube is not being driven; a normal reading with no mark means the beam is being lost in the optics — go to step 6.
5. Power chain: PSU, connections, tube
In rough order of likelihood:
- Loose or corroded connector on the laser-enable or PWM line. Cheapest possible cause; check it before anything else.
- Laser power supply (LPSU) failure. Common, and much cheaper than a tube. If the tube shows no glow at all during a pulse, suspect the PSU first.
- Tube end of life. A CO2 tube that lights with a weak, patchy or pink-ish glow instead of a steady bright discharge is failing. Tube life is typically a few thousand hours and shortens sharply if it is run at 100% continuously.
- High-voltage lead arcing or disconnected — visible scorching or a crackling sound. Power down completely before inspecting.
6. The beam is being made but not delivered
If the tube fires but nothing reaches the material, the beam is being lost on the way:
- Lens installed upside down. A very common post-cleaning fault — the convex face goes up.
- Mirror knocked out of alignment after a crash or a move. Do a tape test at each mirror.
- Filthy or cracked lens. A heavily contaminated lens can absorb almost all the energy — and then crack from the heat.
- Protective film left on a new lens or window.
7. Diode machines specifically
- Wrong firmware / mode: a GRBL machine in M3 constant vs M4 dynamic mode can behave unexpectedly at low speeds. For most diode work M4 is what you want.
- $30/$31 max spindle speed mismatched with the S-value your software sends — if your software sends S1000 and the controller expects S255, effective power lands near zero.
- Weak or shared USB power, or an underspecified supply. Diode modules draw more than people expect; use the supplied brick.
- Safety key or emergency stop not released.
- Module failure — diodes degrade with hours and heat. If the fan stopped working at some point, the module may have cooked.
8. Glowforge specifically
Because the machine is cloud-controlled, the failure modes differ:
- Print appears to run but nothing happens — check the lid and head cables, a known wear point; a partially seated ribbon cable produces exactly this symptom.
- Confirm the window and lens are clean and correctly seated, and the printhead is fully clicked into place.
- An orange button plus a completed-looking print usually points at a hardware fault the app will name — read the specific error rather than guessing.
- Because settings live in the cloud, a “no output” job is frequently a proofgrade/manual settings mix-up rather than hardware.
Still nothing?
Write down what you observed at the test fire in step 4 — mark or no mark, mA reading, whether the tube glowed — before contacting support. That single observation is what separates a settings problem from a PSU problem, and it is the first thing any competent supplier will ask for.
If the beam does fire but the cut does not go through, that is the other guide: why won't my laser cut all the way through? For scorched edges on an otherwise good cut, see how to stop burn marks on wood.
FAQ
My laser runs the job but doesn't cut anything. What's wrong?
If the head tracks the job and the material is completely untouched, there is no beam at all, which is a different fault from a weak cut. Check in this order: the layer is not set to Tool or Output off and power is not zero, the lid interlock is closing properly, and on CO2 that water is visibly flowing and not too warm. Then do a controlled test fire at 15-20% against masking tape to find out whether the tube fires at all.
How do I test whether my CO2 tube is firing?
With the lid closed and a scrap of masking tape or card at the focal point, use the machine's Pulse or Test button briefly at around 15-20% power. A mark means the tube, PSU and optics all work and the fault is in the job or controller path. No mark means the fault is in the power chain. If the machine has an mA meter, watch it: zero mA means the tube is not being driven, while a normal reading with no mark means the beam is being lost in the optics.
Is it the tube or the power supply?
The power supply fails far more often than the tube and costs much less. If the tube shows no glow at all during a test pulse, suspect the LPSU or a loose laser-enable connector first. A tube that lights with a weak, patchy or pinkish glow rather than a steady bright discharge is the one that is genuinely at end of life. Be aware a CO2 PSU holds a lethal charge even unplugged - if you are not trained for high-voltage work, stop here and call the supplier.
Why won't my diode laser fire?
Common causes are a controller mismatch and power. Check the S-value range: if your software sends S1000 while the controller's $30 is set to 255, effective power lands near zero. Confirm the machine is in M4 dynamic mode rather than M3 for normal work, the safety key or emergency stop is released, and you are using the supplied power brick rather than USB power. If the module fan has failed at some point, the diode itself may be cooked.
My Glowforge says it printed but nothing happened.
Check the lid and head ribbon cables first - they are a known wear point and a partially seated cable produces exactly this symptom. Then confirm the window and lens are clean and correctly seated and the printhead is fully clicked in. Because settings live in the cloud, a no-output job is often a proofgrade versus manual settings mix-up rather than a hardware fault, so read any specific error the app reports rather than guessing.
Could the lid switch stop my laser firing?
Yes, and it is one of the most common causes. Almost every enclosed machine refuses to fire with the lid open, and the interlock switch or magnet is a frequent failure point. The signature is that the job runs completely normally with no error shown and no beam is produced. Check the magnet or microswitch is aligned and clean; on many machines you can hear it click as the lid closes.