Epson ET-2760 Error Code 031004 After Mainboard Replacement - Causes and How to Diagnose a Printhead Thermistor Error

Question:
I have an Epson ET-2760 printer where I replaced the mainboard because fuse F301 had blown. After installing the replacement board, the printer now shows error code 031004.

I checked the printhead FPC cable and it appears fine. All 20 pins have continuity with low resistance, and none of the pins are shorted to neighboring pins. The mainboard also appears fine, and F301 tests good. I cannot find any other fuses labeled F### or FU### (F302 is not present). The mainboard assembly number is 2188789 (also labeled 2188788 on the back).

The 031004 error still appears even when the printhead is disconnected. What could be causing this error?

Answer:

Now let's walk through the 031004 error and what it likely means in your situation.

What Error Code 031004 Means

On Epson EcoTank printers like the ET-2760, error code 031004 typically indicates a printhead thermistor circuit error.

The thermistor is a temperature sensor built into the printhead. Its job is to monitor the temperature of the firing elements while printing. If the printer cannot read the thermistor properly, the firmware triggers 031004 as a protective measure to prevent damage.

The printer may report this error when:

1. The printhead thermistor is damaged

2. The thermistor signal path is broken

3. The FFC cable or connector is faulty

4. A board component in the thermistor circuit is damaged

5. The mainboard itself has a fault

Since you already replaced the mainboard due to a blown F301 fuse, the thermistor circuit may have been involved in the original failure.

Step 1: Test the Printhead Thermistor

The first step is to test the printhead electrically.

A thermistor inside the printhead should show a measurable resistance when checked with a multimeter. If the thermistor is open (infinite resistance) or shorted, the printer will trigger 031004.

We provide a testing guide that shows how to measure the printhead using a multimeter:

Printhead Multimeter Test Sheet (https://bchtechnologies.com/products/fa040xx-printhead-multimeter-test-sheet-digital-download-copy?_pos=2&_sid=cfb502072&_ss=r)

If the thermistor reading is abnormal or missing, the printhead itself is defective.

This is actually one of the most common causes of 031004.

Step 2: Inspect the FFC Cable

You already did a continuity test on the 20-pin FPC cable, which is excellent troubleshooting practice.

However, even when continuity appears normal, FFC cables can still fail due to:

• Hairline cracks in the copper traces

• Oxidized contacts

• Partial internal breaks that only fail under load

Because the thermistor signal is very low voltage, even minor resistance issues can trigger the error.

If possible, check:

• Cable ends for wear or carbon marks

• Any bent pins in the board connector

• Loose locking tabs on the connector

If you have a spare cable, swapping it is a quick way to rule this out.

Step 3: Inspect the FFC Connector on the Mainboard

Sometimes the connector itself is the problem rather than the cable.

Check the mainboard connector for:

• Bent pins

• Pins pushed down inside the housing

• Contamination or debris

A single damaged pin in the thermistor line can trigger 031004.

Step 4: Check the Thermistor Signal Path on the Mainboard

If the printhead and cable both test good, the next step is the thermistor signal path on the board.

Even if the board looks clean visually, the issue could be a small surface component such as:

• Pull-up resistors

• Filtering resistors

• Protection resistors

• Analog input circuitry

These components sit between the printhead connector and the microcontroller.

If one of these resistors is open or damaged, the board will fail to read the thermistor and throw 031004.

Since your printer originally blew F301, there is a possibility that a voltage spike also damaged components in this area.

Step 5: Why the Error Appears Even With the Printhead Disconnected

You mentioned the 031004 error still appears with the printhead disconnected, which is actually an important clue.

On many Epson printers:

• A disconnected printhead will also cause the thermistor circuit to read open

• The firmware cannot distinguish between no thermistor signal and a broken thermistor

Therefore, the printer still reports 031004.

So this behavior does not necessarily mean the board is bad. It simply confirms the thermistor circuit is not producing a valid signal.

Most Likely Causes (Based on Your Symptoms)

Given your testing so far, the most common possibilities are:

1. Damaged printhead thermistor (very common after fuse events)

2. FFC cable degradation despite continuity testing

3. Connector pin damage on the mainboard

4. Small resistor failure in the thermistor signal path

In many real-world cases involving a blown F301 fuse, the printhead is the original cause, and the board replacement alone does not solve the problem.

Addressing printer issues can be complicated because many of the problems are mechanical and require hands-on diagnostics. For that reason, we're not able to provide remote troubleshooting or step-by-step repair support beyond general guidance.

We do offer in-person evaluation and repair services through our local diagnostic facility: BCH Printer Repair Service (https://bchtechnologies.com/printer-repair-service). Due to high demand, repairs are handled on a first-come, first-served basis, and it may take a few weeks before we are able to accept a printer drop-off. Our services are structured so you can send in either the entire printer or specific components for testing.

That said, we recognize that professional repair is not always the most economical route. Because of this, we strongly encourage self-help research whenever possible. A good starting point is YouTube, especially our channel homepage: BCH Technologies YouTube Channel (https://youtube.com/@bchtechnologies). Use the search icon next to the About section on the right side of the menu bar to find videos on specific topics. I receive dozens of questions daily asking whether we have a video on certain repairs. After creating videos for more than nine years, it's hard to remember every single topic we've covered, so using YouTube's search feature is often the fastest way to locate helpful content. YouTube may also recommend relevant repair videos from other creators that could assist you.

Thanks again for reaching out and for supporting our work. Your questions help us continue building better repair resources for the entire printer community.