MAXTEMP
Prusa 3D Printer
Severity:What Does This Error Mean?
MAXTEMP means the hotend went past its maximum safe temperature — usually 305°C on the MK3 and MK4, slightly different on other models.
The printer cuts heater power immediately to prevent fire.
The cause is almost always a thermistor that's lost contact with the heatblock, or a heatbreak fan that's failed.
Power off and inspect — don't restart until you've found the cause.
Affected Models
- Prusa MK3S+
- Prusa MK4
- Prusa Mini+
- Prusa XL
- Prusa MK3.5
Common Causes
- Thermistor wire loose or pulled out of the heatblock
- Heatbreak fan failed — heat creeps up and the thermistor reads wrong
- Heater cartridge runaway — failed PID, heater stuck on
- Thermistor itself failed reading low (so the printer kept heating)
- Loose or damaged thermistor wire making intermittent contact
How to Fix It
-
Power the printer off completely.
Hit the power switch.
If the printer triggered MAXTEMP, the firmware has already cut the heater, but full power-off is the right move while you inspect.
Don't try to restart and clear the error — find the cause first. -
Wait for the hotend to cool.
Even with the heater off, the hotend takes 10–15 minutes to drop below 100°C.
Don't touch anything until it's cool enough to handle.
The aluminium heatblock holds heat well past when the LCD shows lower numbers. -
Inspect the thermistor wire.
The thermistor is the small bead in a glass or ceramic sleeve, secured to the heatblock with a small screw or by friction.
Check that the wire goes all the way into the heatblock and the screw is tight.
A thermistor that's vibrated loose is the most common MAXTEMP cause. -
Check the heatbreak (parts cooling) fan.
The smaller fan on the toolhead — the one cooling the heatbreak above the hotend — should spin whenever the hotend is above 50°C.
If it's not running, heat creeps up the heatbreak and the thermistor reads low.
Replace if it's seized or running slowly. -
Reseat or replace the thermistor.
If the wire is loose, push it firmly back into the heatblock and tighten the screw.
If the thermistor is damaged or you've had multiple MAXTEMP events, replace it — Prusa thermistors are $10–$20 and a 5-minute swap once the toolhead is open.
When to Call a Professional
MAXTEMP is a fire-safety event.
Don't restart the printer until you've physically inspected the hotend.
If you're not comfortable opening the toolhead, contact Prusa support — they can guide you through diagnosis or arrange repair.
Frequently Asked Questions
Can MAXTEMP cause a fire?
Yes — that's why MAXTEMP exists as a safety cutout.
If the heater stays on uncontrolled long enough, plastic parts of the toolhead can melt and combust.
Modern Prusa firmware catches MAXTEMP within seconds, but never override or disable the protection.
Treat every MAXTEMP event as serious.
How often should I check the thermistor?
Every spool change is a good habit.
While loading filament, take a moment to confirm the thermistor wire is secure and the screw holding it is tight.
Vibration during prints loosens it over time, especially on the moving toolhead of an MK3 or MK4.