No extrusion at the start of a print — nothing comes out of the nozzle, 5 causes

Symptom: the printer heats up normally, performs its homing move, sets off on the first layer — and nothing. The nozzle travels across the bed dry, no skirt appears, and the extruder may be clicking while it does so or running completely quietly. Sometimes the material only shows up after half a minute or so, when the model is already halfway through its first layer.

In this situation it is worth separating two possibilities straight away. Either the plastic is not reaching the nozzle at all, or it is reaching it but has no way out. The first group of causes lies with filament feeding and a clear path, the second with first-layer geometry. Telling them apart takes a few seconds: heat the nozzle to working temperature and extrude 20 mm of material from the printer menu, holding the head high above the bed. If the material comes out as an even, straight string, the path is clear and calibration is at fault. If it does not come out, or emerges as a thin twisted strand, the problem is mechanical.

The most common causes and their fixes

1. The extruder was not primed before the start

After every filament change and after every longer pause, an empty space is left in the hot nozzle. Before plastic flows into it and rebuilds the pressure, the printer will have travelled several dozen millimetres of path. If the profile contains no skirt or priming line, that distance falls exactly on the model's first layer.

What to do: turn on a skirt — two loops around the model are enough to stabilise the flow and, incidentally, to show whether the first layer is properly levelled. Check as well whether the starting G-code contains a purge line at the edge of the bed. After every spool change, extrude enough material by hand for clean strands of an even colour to come out of the nozzle.

2. The nozzle sits so close to the plate that the material has no way out

With a zero gap the nozzle orifice is simply covered by the surface of the bed. The plastic then backs up the channel, the extruder starts skipping, and at the height of the second or third layer the print suddenly gets going as if nothing had happened. This is the most misleading version of the problem, because the printer is technically in working order.

How to check: stop the print, move the head up 1 mm on the Z axis, and extrude material by hand. If it now flows out without resistance, you have your answer.

What to do: raise the Z-offset by 0.02–0.05 mm and repeat. Look for the point at which the skirt lines are flattened and joined but continuous. While you are at it, check whether a dried blob of plastic has collected on the nozzle — it can throw off the probe reading and set the head lower than the settings suggest.

3. The nozzle is clogged

A blockage most often forms at the end of the previous print and reveals itself at the start of the next one. Typical sources are charred residue after printing at a high temperature, specks of dust dragged in along with the filament, and leftovers of a material with a different melting point — the classic case being PLA left in a nozzle through which nylon is then forced.

How to check: extrude material into the air. A stream that curls off to one side or comes out noticeably thinner than the nozzle orifice means a partial blockage.

What to do: perform a cold pull: heat the nozzle to the top of the material's range, feed the filament in by hand, then lower the temperature gradually and pull the filament out in one decisive movement the moment it begins to resist noticeably. Repeat until you see a clean imprint of the channel on the tip. You will not clear a blockage with a needle when cold — all you will do is widen the orifice.

Note: abrasive materials destroy brass within a few dozen hours of work. PLA/CF and ABS/CF require a hardened nozzle, and with PLA Wood and nylon the wear is moderate, so the nozzle should be checked periodically.

Porima material	Nozzle temperature	Recommended nozzle	Abrasiveness
PLA	200–230 °C	0.4 mm	none
Tough PLA	210–240 °C	0.4 mm	none
Hyper PLA+	220–250 °C	0.4 mm	none
Silk PLA	230–260 °C	0.4 mm	none
PLA Wood	210–240 °C	0.6 mm	moderate
PLA/CF	220–250 °C	0.4 mm, hardened	very high
PETG	240–260 °C	0.4 mm	none
HT PETG	270–300 °C	0.4 mm	none
ABS	250–280 °C	0.4 mm	none
ASA	250–280 °C	0.4 mm	none
PA (nylon)	260–290 °C	0.4 mm	moderate
TPU Flex 98A	230–260 °C	0.4 mm, direct drive recommended	none

Source: the official FDM technical data table from the manufacturer, Porima. The full set of 25 materials: print temperature table.

4. The drive wheel is not gripping the filament

The extruder turns but the filament stays put. Where it meets the knurled wheel you will then see a chewed, flattened groove and specks of debris inside the extruder body. There are several possible reasons: too little spring pressure, a worn or debris-clogged knurl, or pressure so high that soft plastic has been crushed. With TPU a moment's inattention is enough for the filament to buckle and escape the guide path.

What to do: take the filament out, cut off the damaged section at an angle and clean the knurl with a brush or compressed air. Set the pressure to a middle value: the filament should be driven confidently but without a deep indentation. With flexible materials reduce the pressure and slow down — TPU Flex 98A prints slowly and works best with a direct drive extruder.

5. The filament has run out or snapped in the guide tube

The most banal cause, and one of the most common on overnight prints. The tail of the filament can be left inside the Bowden tube, and a printer with no filament runout sensor will happily carry on working dry. A separate version of this is a break: filament that has lain unwound for several months turns brittle and snaps in the curve of the guide or right by the spool.

What to do: check the whole path from spool to head and remove the broken section. Check too whether the filament has been pulled under its own coil on the spool — a knot like that blocks feeding just as effectively as a clogged nozzle, and you only find it after unwinding a few metres. Store filament in a sealed container with desiccant; moisture and age are the main causes of brittleness.

Quick checklist

Extrude 20 mm of material into the air and judge the stream.
Check that the filament is continuous along the whole path.
Inspect the extruder knurl and clean out the debris.
Raise the Z-offset by 0.02–0.05 mm and check the skirt.
Do a cold pull if the stream is thin or twisted.
Turn on the skirt in the profile and a purge line in the starting G-code.
Check that the nozzle temperature matches the material in the table above.

The overriding rule: change one parameter at a time. Stripping down the hotend and correcting the Z-offset in one go usually ends in two new faults.

When the cause lies deeper in the hotend

If a cold pull does not help and the problem comes back after every filament change, check the joint between the PTFE tube and the nozzle. A gap of a fraction of a millimetre is enough for plastic to collect in it and form a plug as it cools. The tube should be cut square and pushed fully home with the nozzle hot, and then the nozzle itself tightened hot as well. It is also worth remembering that PTFE degrades at high temperatures — with HT PETG (270–300 °C), nylon and PC/ABS an all-metal heat break is not a luxury but a condition of stable operation.

The second thing that only shows up over time is a temperature set too low "to save energy". Every material has a threshold below which it does not reach the required fluidity, and on the first layer — printed slowly, on a heater block that is still cold — that shows up most sharply. Before you start hunting for mechanical faults, make sure you are inside the range given by the manufacturer.