Epson L1800 Two Flashing Lights and Error 0x43: Printhead Thermistor and Mainboard Troubleshooting

Question

I have an Epson L1800, and both the ink and paper lights are flashing at the same time. I tried using a reset or adjustment program, selected the partial reset option, and attempted to check the printer's status. However, the program displayed an error message and did not show any values in the two counter fields, which normally display values such as 0 and 80.

What could be causing the two flashing lights, and why is the reset utility unable to read the printer's values?

Answer

When the paper and ink lights on an Epson L1800 flash together, the printer is reporting a general service or hardware error. The light pattern alone does not identify one specific failure, so the actual error code normally needs to be read through an Epson adjustment program, service utility, or diagnostic software.

Based on the symptoms you described, one likely possibility is error 0x43.

What Error 0x43 Usually Means

On the Epson L1800, error code 0x43 commonly indicates that the mainboard cannot correctly detect the printhead thermistor circuit.

The thermistor is a temperature-sensing component associated with the printhead. It allows the printer's mainboard to monitor printhead temperature and protect the head from overheating or operating under unsafe electrical conditions.

If the mainboard does not receive the expected thermistor signal, the printer may stop during startup and flash both warning lights. This protection is intentional because continuing to operate the printer without reliable temperature feedback could damage the printhead, the head driver circuit, or the mainboard.

The problem may involve the printhead itself, the flat flexible cables, a loose connection, contamination, corrosion, or damage to the mainboard.

Possible Causes of Error 0x43

Loose or Incorrectly Installed Printhead Cables

The L1800 printhead connects to the mainboard through flat flexible cables, commonly called FFC cables.

If one of these cables is not inserted fully, is installed at an angle, or is placed into the wrong connector, the mainboard may be unable to read the thermistor signal.

This often happens after:

• Replacing the printhead

• Removing the carriage

• Cleaning ink around the printhead

• Servicing the capping station

• Disconnecting the printhead cables

• Converting the printer for DTF use

Turn the printer off and disconnect it from power before inspecting these cables. Check that each cable is inserted straight and completely into its connector. The exposed contacts must face the correct direction.

Do not repeatedly reconnect the cables while the printer is powered. Doing so can damage the printhead driver circuit or create a short circuit on the mainboard.

Damaged or Contaminated FFC Cables

Ink, cleaning fluid, moisture, or corrosion on the cable contacts can interrupt the thermistor circuit.

Carefully inspect both ends of every printhead cable. Look for:

• Burned contacts

• Black marks

• Green or white corrosion

• Torn traces

• Creased cable sections

• Missing or damaged contact pads

• Ink contamination

• Cleaning solution residue

A cable may appear normal from the front while having a cracked conductor near a fold or connector. If there is any doubt, replacing the cable may be necessary.

Never install a wet or contaminated cable into the mainboard. Even a small amount of conductive liquid can create a short circuit and damage the head driver components.

Printhead Thermistor Failure

The thermistor circuit may have failed inside the printhead itself.

This can happen because of:

• Internal printhead damage

• Electrical shorting

• Liquid entering the printhead electronics

• Overheating

• Incorrect cable installation

• A defective replacement printhead

• Damage caused by connecting or disconnecting the head while powered

If the thermistor is open, shorted, or outside the expected resistance range, the mainboard may report error 0x43 immediately.

In this situation, resetting the waste ink counter will not solve the problem because 0x43 is a hardware-detection error rather than a maintenance-counter error.

Mainboard Printhead Driver Damage

The mainboard contains circuitry responsible for communicating with and driving the printhead. If this circuit is damaged, the board may fail to detect the thermistor even when the printhead and cables are good.

Mainboard damage can result from:

• A shorted printhead

• Ink or cleaning fluid reaching the board

• Installing cables while the printer is powered

• Reversing an FFC cable

• Using a damaged printhead

• Electrical surges

• A failed fuse, transistor, resistor, or head driver component

A damaged printhead can also damage a replacement mainboard. Likewise, a defective mainboard may damage a good printhead. For this reason, swapping expensive parts without testing carries a significant risk.

Incorrect Printhead or Incompatible Replacement Part

Some replacement printheads may physically fit the L1800 but have different internal electrical characteristics or may already be defective.

If the problem began immediately after installing another printhead, confirm that the head is correct for the printer model and that it came from a reliable source.

A used printhead may have clogged nozzles and still pass electrical testing, while another head may appear clean but contain a failed thermistor or internal short.

Why the Reset Program Shows No Counter Values

The two fields you mentioned, which may normally show values such as 0 and 80, are likely maintenance or waste ink counter readings.

If the program displays no values, it may mean the software cannot communicate correctly with the printer. It does not necessarily mean the counters are zero.

A hardware error such as 0x43 may prevent the printer from entering the normal state required for the adjustment program to read or reset the counters.

The utility may also fail because of one of the following issues:

• The wrong printer model was selected

• The wrong USB port was selected

• The printer driver is not installed correctly

• The adjustment program is incompatible with the operating system

• The printer is connected through Wi-Fi instead of USB

• The USB cable or USB port is unreliable

• Another printer utility is interfering with communication

• The printer is stuck in a fatal hardware-error state

• The program is blocked by antivirus software or Windows permissions

For service utilities, connect the printer directly to the computer with a USB cable. Avoid USB hubs, adapters, network connections, and wireless printing during diagnosis.

Open the utility and confirm that the selected port matches the Epson L1800. If the program provides an "Auto Selection" option, try that first. You may also check Windows Device Manager or the printer properties to confirm which USB port is assigned.

However, if the printer has a true 0x43 hardware fault, correcting the software connection may allow you to read the error, but it will not repair the underlying thermistor problem.

Partial Reset Versus Hardware Repair

A partial reset normally affects stored settings, maintenance information, or initialization data. It does not repair a broken thermistor circuit, damaged cable, failed printhead, or defective mainboard.

Waste ink reset procedures are useful when the printer reports that its ink pads have reached the end of their service life. That condition often presents as a service-required message or a counter-related error.

By contrast, error 0x43 is generally associated with the printhead temperature-detection circuit. Therefore, repeatedly resetting the printer is unlikely to help and may make diagnosis more confusing.

Recommended Inspection Order

Begin with the least invasive checks.

First, unplug the printer and inspect the printhead FFC cables. Confirm that they are clean, undamaged, correctly oriented, and fully inserted.

Next, inspect the printhead connector area for ink or cleaning-fluid contamination. If liquid is present, do not power the printer until the area has been properly cleaned and completely dried.

Then inspect the mainboard connectors and surrounding components for burned marks, corrosion, or liquid damage.

If the error began after replacing or servicing the printhead, concentrate on the cable orientation, cable condition, and printhead compatibility.

If all connections appear correct and the printer still produces error 0x43, the next likely suspects are the printhead thermistor circuit or the mainboard's printhead-detection circuitry.

Testing these components safely may require electrical measurements, known-good parts, and experience diagnosing Epson head circuits.

Be Careful When Swapping the Printhead or Mainboard

Do not install a new mainboard without considering whether the printhead caused the original failure.

A shorted printhead may damage the replacement board as soon as the printer is powered on. Similarly, installing a good printhead into a damaged board could place the replacement head at risk.

Before replacing either component, inspect for shorts, damaged cables, conductive ink residue, and burned driver components. If possible, test the head and board independently or use known-good components under controlled conditions.

Always disconnect the printer from power before touching the FFC cables, printhead connectors, or mainboard.

Addressing printer problems can be difficult because many failures require direct, hands-on inspection and testing. For that reason, we are not able to provide individualized remote troubleshooting, ongoing repair guidance, or step-by-step support for printer repairs.

We do offer in-person evaluation and repair through our local printer diagnostic and repair facility [https://bchtechnologies.com/printer-repair-service]. Because demand is high, service is provided on a first-come, first-served basis, and it may take several weeks before a printer can be scheduled for drop-off. Our services are structured to handle either a complete printer or certain removable parts, and the service page explains how to proceed.

We understand that professional repair service may not be the most economical choice for every customer. Therefore, we strongly recommend using online research and self-help resources whenever you are comfortable doing so.

You can begin by searching YouTube or visiting the homepage of our BCH Technologies YouTube channel [https://youtube.com/@bchtechnologies]. Use the search icon near the "About" section on the right side of the channel menu to look for terms such as "L1800 0x43," "L1800 thermistor error," "L1800 printhead cable," or "L1800 two flashing lights."

We receive dozens of questions each day asking whether we have a video covering a particular repair. Since we have created videos for more than nine years, it is difficult to remember every video and title. Using YouTube's search function is usually the most efficient approach. YouTube may also recommend helpful videos from other channels that cover similar symptoms.

Thank you again for contacting BCH Technologies and for your kind words and support. We truly appreciate your patience. We hope this explanation helps you understand why the reset utility is not displaying the counter values and why error 0x43 should be treated as a possible printhead thermistor, cable, or mainboard communication problem.