Form 4: cartridge and resin level errors (1.6.2, 1.9.4, 1.9.5, 1.9.6, 1.9.22, 1.9.23)

Symptom

The Form 4 or Form 4L will not start or pauses the print with a cartridge or resin level error: 1.6.2 (cartridge is missing), 1.6.27 (cartridge mismatch), 1.9.4 (could not measure resin level), 1.9.5 (tank is overfilled), 1.9.6 (not enough resin to finish print), 1.9.7 (paused due to low resin), 1.9.22 (cartridge is empty) or 1.9.23 (cartridge is dispensing slowly); or it shows a cartridge level that is not real.

Likely causes, from most to least likely

1. The cartridge is empty or was removed during the print: each cartridge reliably dispenses one litre of resin.
2. The bite valve under the cartridge does not open or has swollen (Tough family resins swell it over time), the vent cap is closed, or the resin is poorly mixed or cold.
3. The resin level sensor (LevelSense, next to the camera, pointing at the back-left corner of the tank) has resin on it, is obstructed or needs recalibrating; bubbles and an unlevel printer also play a part.
4. The cartridge floor load cell measures wrongly, or resin was poured into the tank by hand.
5. The resin in the cartridge does not match the job (different material type or version).
6. The cartridge RFID sticker is damaged or missing, or the RFID cable is loose.

Checks to tell which one it is

• Note the exact code: the 1.6 series are consumables errors and the 1.9 series are dispensing and resin level errors. On the Form 4L, the left and right cartridge equivalents are 1.9.9 and 1.9.10 (empty) and 1.9.11 and 1.9.12 (dispensing slowly).
• Take out the cartridge: check that the vent cap is open, that there is resin left and that the valve underneath opens when squeezed.
• With a mirror, look for resin drops on the level sensor or anything between the sensor and the tank.
• In Settings → Tools → Level printer, check whether the printer is level.

Before you start

Uncured resin irritates skin and eyes: wear nitrile gloves and safety glasses, ventilate the room and do not look at the UV light. Before taking anything apart or cleaning it, switch the printer off and unplug it, unless a step says otherwise. If in any doubt, stop and ask a professional.

Step-by-step fix

1. Cartridge, vent cap and valve

   Wearing gloves, reinsert the cartridge if you removed it or replace it if it is empty. Open the vent cap, shake the cartridge to mix the resin and check that the bite valve opens when squeezed. For Tough resins that dispense slowly, Formlabs suggests printing and fitting a cartridge shim. Keep the printer and resin between 18 and 28 °C.

   Check: The printer refills the tank and carries on printing.

   If that does not fix it: Try another cartridge: if it works, the problem was the cartridge.

2. Clean the level sensor

   Check that nothing blocks the level sensor or the space down to the tank. If there is resin on the sensor (use a mirror to look up at it), clean it with a lint-free cloth dampened with isopropyl alcohol. If the error happened once, retry: it may have been bubbles.

   Check: Error 1.9.4 or 1.9.5 does not come back.

   If that does not fix it: Level the printer (next step).

3. Level the printer

   Go to Settings → Tools → Level printer, follow the screen and use the levelling tool.

   Check: The screen shows the printer is level.

   If that does not fix it: Recalibrate the level sensor (next step).

4. Recalibrate the level sensor

   Remove all consumables. In Settings → Tools → Calibration → Resin Level Sensor, press Start and place a flat plastic card without embossing where the screen shows: on the Form 4, with its long side aligned with the left side of the cutout below the camera; on the Form 4L, with the left edge of the LPU. Press Next and Calibrate, do not move the printer and remove the card when it finishes.

   Check: Calibration successful appears.

   If that does not fix it: If the cartridge level still does not add up, check the tracking (next step).

5. Cartridge level wrong or cartridge not detected

   Update PreForm and the firmware (version 1.17 or later improves resin tracking), do not pour resin into the tank by hand and recalibrate the cartridge floor load cell. If the cartridge is not detected, reboot, try another one and check that yours has the RFID sticker (a small square you can feel under the label).

   Check: The level shown matches the real resin and the cartridge is detected.

   If that does not fix it: The RFID board, LevelSense board or cartridge floor may need checking or replacing using Formlabs repair guides: send the logs to support or your reseller.

6. Resin does not match the job

   For 1.6.27, insert a cartridge with the same resin and the same material version as the job; if it already matches, reboot, update PreForm and the firmware, and regenerate and re-upload the job.

   Check: The print starts without the warning.

   If that does not fix it: Test the cartridge in another printer, if you have one, to rule out the RFID board.

Prevention

• Leave the vent cap open while printing and shake the cartridge before use.
• Do not refill the tank by hand: it throws off resin tracking.
• Keep the level sensor clean and the printer level.
• Print with the room and resin between 18 and 28 °C.

Still not fixed?

Tell usi3d's AI about your case: choose your printer, describe what you see and add photos if you like. It proposes checks step by step, with their sources.

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Printers it applies to

The Formlabs Form 4 family: Form 4 and Form 4L.

Official sources

This guide summarises the official documentation linked here:

• Form 4 and Form 4L generation error messages · Formlabs
• Calibrating the resin level sensor (Form 4 and Form 4L generation) · Formlabs
• Resin cartridge not detected properly (Form 4 and Form 4L generation) · Formlabs
• Cartridge fullness tracking is incorrect (Form 4 generation) · Formlabs