Epson ET-8550 DTF Conversion Error 031004 After Damper Box Swap: Causes, Thermistor Checks, and What to Inspect Before Adding Ink

Question

My Epson ET-8550 is brand new and worked fine before I started the DTF CISS conversion. The printer has never had ink put into it yet, and there's no debris or dirt inside. The person I bought the DTF CISS from told me to replace the Y-tube and swap the damper box and dampers with parts he sent, even though I originally followed his video.

Now the printer keeps showing error code 031004. The first dampers he sent wouldn't "pop in" at all, so he sent smaller ones that fit perfectly. But the damper box the dampers sit in is a KJS model-could that be why I'm getting error 031004? I also swapped the damper box and gold plate to the KJS model.

Answer

What error code 031004 means on the Epson ET-8550

On the Epson ET-8550, error code 031004 is a head temperature error. In simple terms, the printer believes the printhead is overheating or is reading an abnormal temperature signal.

This is not a "dirt/debris" type error, and it's also not an "ink hasn't been added yet" type error. This code is triggered by the printer's electronics-specifically the temperature sensing circuit in the printhead system.

Why a damper box swap can trigger a head temperature error (even with no ink installed)

It's very understandable to suspect the KJS damper box, because that's the part you changed right before the error appeared. However, it's important to separate two things:

• Ink delivery parts (damper box, dampers, Y-tube, ink lines)

• Electrical head protection/temperature feedback (printhead thermistor circuit, head FFC cable, mainboard driver circuitry)

Error 031004 is primarily an electrical feedback error, not an ink-flow error.

That means a KJS damper box by itself usually does not directly cause 031004-because the printer isn't measuring damper box "brand/model," it's measuring an electrical temperature signal.

But the damper box swap can indirectly cause 031004 because the process of swapping dampers and the gold plate usually involves working very close to the printhead, its wiring, and its FFC connections.

Common "conversion-related" triggers include:

1) Printhead FFC cable not seated perfectly (most common after swaps)

The ET-8550 uses fine-pitch Flexible Flat Cables (FFC). If the cable is not inserted fully, inserted slightly crooked, or the latch is not locked, the temperature feedback signal can read incorrectly.

Even if the printer is brand new, a slightly loose FFC can cause the mainboard to interpret the thermistor signal as "over-temp."

2) Damaged FFC (crease, nick, contamination, or burn)

FFC cables can be damaged without obvious symptoms. A tiny crack in a trace can cause abnormal resistance/voltage readings.

Also, during conversions, it's possible to accidentally pinch the cable or rub it against an edge.

3) Thermistor line short/open (printhead-side fault)

At startup, the printer sends a test pulse and reads back the thermistor (temperature sensor) voltage behavior. The thermistor is designed to change resistance with temperature. If the printer reads a value that indicates "too hot" or "shorted," it will throw 031004 as a protective shutdown.

This can happen due to:

• A true printhead thermistor failure (rare but possible even on a new unit)

• A short caused by a damaged cable or connector

• Liquid/grease/contamination on contacts (skin oil, residue, ink from handling other parts, etc.)

4) Mainboard driver/reading circuit problem (less common, but possible)

If the printhead is good and the cable is good, the mainboard may be misreading the thermistor input. This is less common than cable/head issues, but it does happen-especially if there was a short event during installation.

Does the KJS damper box cause 031004?

In most cases: no-031004 is not caused by the damper box "model."

However, there is a practical compatibility issue worth mentioning:

• If a damper box/damper set doesn't physically mate correctly, users sometimes apply pressure or force alignment.

• That forcing can flex the printhead assembly area or disturb nearby cables and connectors.

• That's one way a damper swap can lead to a head temperature error even though the damper box isn't the "electronic cause."

So your observation that the first dampers didn't pop in, then smaller ones fit, is a strong hint that there may have been mechanical stress or repeated handling in the head area-exactly where the temperature-sensing wiring lives.

What to inspect (before adding any ink)

Since the printer has never had ink, you're actually in the best-case scenario for troubleshooting because you can focus on electronics and installation quality without worrying about ink contamination.

Here's what typically matters most for 031004:

1. Printhead FFC cable

• Power off, unplug the machine.

• Inspect both ends of the FFC: look for dark spots, scorch marks, crease lines, or damaged edges.

• Reseat the cable carefully and evenly, and make sure the latch is locked.

1. Connector condition

• Check for bent contacts, debris, or residue in the connector.

• Even small contamination can create false readings.

1. Signs of heat or short

• Any "burnt electronics smell," discoloration, or melted plastic near the head cable path is a red flag.

• If you see burn marks, the FFC usually needs replacement, and the printhead may also be damaged.

What the printer is "thinking" when it shows 031004

At the beginning of operation, the printer checks head temperature using the thermistor circuit. If the voltage feedback suggests the head is at an abnormally high temperature (often consistent with a short or failed sensor circuit), the printer protects itself by stopping and posting 031004.

That's why this error often points to:

• A failed printhead, or

• A damaged FFC cable, or

• A mainboard issue (if head/cable test good)

Likely outcome and what usually fixes it

In many cases, 031004 means the printhead is no longer usable and must be replaced, especially if reseating the FFC and checking the connector doesn't change anything.

When replacing the printhead, it's also strongly recommended to inspect (and often replace) the printhead FFC cable if there is any sign of heat damage, discoloration, or compromised traces-because a damaged cable can kill a new printhead or keep the same error going even after a head swap.

Addressing printer issues can be a complicated affair due to the hands-on nature of the problems. So, we're not able to provide remote troubleshooting, suggestions, or support for printer repairs. We do offer an in-person evaluation and repair service via our local diagnostic facility: Printer Repair Service (https://bchtechnologies.com/printer-repair-service). Given the high demand, we operate on a first-come, first-served basis, so it may take a few weeks before we can schedule a drop-off. Our services are structured to repair either a whole printer or specific parts, with clear instructions on how to proceed. However, we acknowledge that our rates aren't the most economical. Thus, we highly recommend that you resort to self-help via online research. You can start by checking out YouTube or visiting our YouTube channel's homepage: BCH Technologies on YouTube (https://youtube.com/@bchtechnologies). Look for specific videos using the search icon next to "About" on the right-hand side of the menu bar. I receive dozens of queries every day asking about videos for specific topics. Having created videos over the past nine years, it's challenging to remember every single one. Therefore, using YouTube's search function would be most efficient. Plus, YouTube might suggest relevant videos from other channels that could assist you.

Thank you again for reaching out and for supporting BCH Technologies. I truly hope this helps you understand what 031004 is signaling and why it can appear right after a damper box swap, even before any ink is added.