HMS 0300-1E00-0001-0002: left nozzle heater open circuit
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HMS 0300-1E00-0001-0002 means the left nozzle heater reads as an open circuit: the printer sends current and nothing comes back. That is the opposite fault to a short, and it points somewhere different. A heater element sealed inside a block rarely goes open on its own; a connector on a toolhead that moves millions of times regularly does.
Affected machines: H2 series. The left half will not heat, so anything that uses the left tool stops. Single-material prints assigned to the right nozzle still run, which gives you time to diagnose properly instead of guessing.
Where to buy
Where an open circuit actually happens
The connector, most of the time. A pin that has backed out of its housing, a crimp that was never fully closed, or a plug that was not pushed fully home after a hotend change. All three read as open and all three cost nothing to fix.
The cable second. The toolhead loom flexes on every move, and a conductor that has fatigued inside its insulation gives an intermittent open that comes and goes with position. That is the most confusing version of this fault and the reason to measure at more than one point.
The element last. If the heater reads open at its own connector, with the plug removed, the element has failed and the hotend assembly is the fix.
Left nozzle will not heat and the printer reports the heater as open circuit
Connector not seated, a fatigued conductor in the toolhead loom, or a failed heater element
- Power off at the wall and let both hotends cool completely.
- Unplug the left hotend and inspect both halves of the connector for a pin sitting low in its housing.
- Measure the heater at the hotend side. Compare with the right-hand heater as a reference.
- If the heater reads healthy at the hotend, reseat the plug and measure again at the board end to isolate the cable.
- Move the toolhead through its travel by hand while watching the reading, to catch an intermittent break.
- If the heater reads open at its own connector, fit a replacement hotend assembly.
Reseat before you order. A surprising share of these are a connector that looked fine, and five minutes with the plug out costs less than a part you did not need.
The short-circuit version is left nozzle heater short circuit, and the single-nozzle equivalent is hotend heater open circuit. Our pages on the hotend and dual nozzle printers cover the hardware.
HMS 0300-1E00-0001-0002 FAQ
Can I keep printing on the right nozzle?
For single-material jobs on the right tool, yes. Tool changes will stop.
How do I tell the connector from the element?
Measure at the hotend with the plug removed. Healthy there means the fault is further back.
Why does it come and go?
That is the signature of a fatigued conductor in the moving loom rather than a failed heater.
Is the left hotend the same part as the right?
On these machines yes, which makes swapping sides a valid test if you have a spare.
LayerWalker
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