Marlin PID Tuning Guide: Fix Temperature Swings & Thermal Runaway

If you have ever watched your 3D printer’s temperature graph and seen it waving up and down like a rollercoaster, you have a PID problem.

Temperature stability is the backbone of high-quality prints. If your hotend fluctuates by even a few degrees, the plastic’s viscosity changes, leading to inconsistent extrusion. Equally important is your heated bed; if it oscillates, the build plate expands and contracts, causing visible horizontal lines or causing parts to warp and detach from the bed. In the worst case, instability in either heater triggers the dreaded "Thermal Runaway" error that halts your print mid-way.

Fortunately, Marlin firmware has a built-in "Autotune" feature that fixes this. It’s called PID Tuning. It essentially teaches your printer how to handle its own heating elements intelligently, rather than just blasting power blindly.

In this guide, we will walk through exactly how to calibrate these settings to get that temperature line dead flat.

What is PID? (The "Cruise Control" Analogy)

PID stands for Proportional, Integral, and Derivative.

Without getting bogged down in calculus, think of it like the cruise control in your car. If you want to go 60 MPH, you don't floor the gas until you hit 60 and then slam on the brakes. You apply variable gas to maintain speed smoothly, adjusting for hills (external cooling) and wind (fans).

Old-school printers used "Bang-Bang" heating—full power ON or full power OFF. This causes temperatures to swing wildly. PID allows the printer to feather the power—applying 100%, then 50%, then 2%—to keep the temperature rock steady.

Tuning Your Hotend

Marlin makes this surprisingly easy with the M303 command. This tells the printer to heat up, cool down, and analyze how the heater responds to power changes.

Step 1: Turn on Your Part Cooling Fan

This is the most common mistake people make. You print with your fan on, so you must tune with your fan on. If you tune with the fan off, your printer won't account for that extra cooling air, and your temperature will plummet as soon as the fan kicks on during a real print.

Step 2: Run the M303 Command

In your terminal, you will send a command that tells the printer: "Run autotune (M303) on the first extruder (E0) at 210 degrees (S210) for 10 cycles (C10)."

Send this command in your terminal:

M303 E0 S210 C10

Your printer will now cycle the heat. Watch the terminal output; you will see it reporting "PID Autotune start." This process usually takes 5–10 minutes.

Step 3: Get Your Values

Once the 10 cycles are done, the terminal will output a final result that looks like this:

Kp: 22.20 Ki: 1.08 Kd: 114.00
PID Autotune finished! Put the last Kp, Ki and Kd constants from below into Configuration.h

Write down those three numbers (Kp, Ki, and Kd).

Step 4: Apply and Save

Now you need to tell the printer to use these new numbers using the M301 command.

Example (Use YOUR numbers, not these):

M301 P22.20 I1.08 D114.00

Finally, and most importantly, you must save this to the printer's memory (EEPROM). If you turn the printer off without saving, you lose the tune.

M500

Tuning Your Heated Bed

Many people skip tuning the bed, but a fluctuating bed causes the printers build plate to expand and contract. This can lead to "Z-banding" (horizontal lines) or cause prints to detach and warp due to inconsistent adhesion.

The process is nearly identical to the hotend, but we use E-1 to select the bed.

Step 1: Run the Autotune

We recommend tuning the bed to your most common printing temperature—typically around 60°C for PLA, 80°C for PETG, or 100°C for ABS.

M303 E-1 S60 C10

Step 2: Apply the Values

Once the process finishes, grab your Kp, Ki, and Kd values. Note that for the bed, we use M304 to apply them (M301 is for hotends, M304 is for beds).

Example (Use YOUR numbers, not these):

M304 P120.43 I2.15 D890.22

Step 3: Save

M500

Troubleshooting Common Errors