8818H Thermostat Error Codes – E1, E2, Err Troubleshooting Guide

In this article, you will learn:

What the E1, E2, and Err error codes mean
How to check and fix sensor faults
How to reset the thermostat to factory settings
How to verify wiring and power connections
When to contact technical support

Click any topic above to jump directly to that section.

This guide covers common 8818H thermostat error codes, including E1, E2, and Err, with step-by-step troubleshooting steps for installers. If you are installing or maintaining an 8818H series heating thermostat, you may encounter error codes on the display. These codes are designed to help you quickly identify the root cause of a problem — whether it is a sensor issue, a wiring fault, or a configuration error.

This guide covers the most common faults on 8818H thermostats and provides step‑by‑step solutions for installers and facility managers.

Common Error Codes: E1, E2, and Err

The 8818H thermostat error codes are displayed by a built‑in diagnostic system when a fault is detected. Understanding these codes is the first step in troubleshooting.

Error Code	Meaning	Likely Cause
E1	Internal sensor fault	The built‑in temperature sensor is short‑circuited, disconnected, or damaged
E2	External sensor fault	The external floor sensor is not connected, short‑circuited, or damaged
Err	Both sensors faulty	Both internal and external sensors are reporting errors simultaneously

When an error code appears, the thermostat will typically lock the heating output and stop operation until the fault is cleared.

Step 1: Check and Reset the Thermostat

Before opening any wiring or replacing components, start with a simple reset.

Turn off the thermostat using the power button.
Wait 30 seconds.
Turn the thermostat back on.

If the error code disappears, the fault may have been a temporary glitch. If the code returns, proceed to the next step.

Step 2: Inspect Sensor Connections

Sensor faults are the most common cause of E1 and E2 errors.

For E1 (Internal Sensor)

The internal sensor is built into the thermostat body.
Check whether the sensor wiring inside the unit is loose or disconnected.
If the thermostat has been opened recently, verify that the sensor connector is properly seated.

For E2 (External Floor Sensor)

The external sensor is connected to the thermostat via terminal blocks — typically labeled for a floor sensor.
Verify that the sensor wires are securely connected to the correct terminals.
Check the sensor cable for visible damage, cuts, or kinks.

For Err (Both Sensors)

This indicates that both sensors are reporting faults simultaneously.
Check both the internal and external sensor connections.
If both connections appear secure, the issue may be with the thermostat’s control board.

Step 3: Test the Sensor with a Multimeter

If the connections appear intact, the sensor itself may be faulty. You can verify this with a digital multimeter.

Turn off power to the thermostat.
Disconnect the sensor wires from the terminals.
Set the multimeter to the resistance (Ω) mode.
Measure the resistance across the sensor leads.

At room temperature (approximately 25°C), a working NTC 10K sensor should read around 10kΩ. If the reading shows open circuit (OL) or a very low resistance (near 0Ω), the sensor is damaged and needs replacement.

Step 4: Verify Power Supply and Wiring

Sometimes error codes are caused by power supply issues rather than sensor faults.

Confirm that the thermostat is receiving the correct supply voltage (220V ±10% 50Hz).
Check that the neutral and live wires are connected to the correct terminals — reversed wiring can cause erratic behavior.
Inspect all terminal connections for looseness or oxidation.

A simple power cycle (turning the thermostat off and on after 30 seconds) can sometimes clear errors caused by voltage fluctuations.

Step 5: Restore Factory Settings

If the error persists after checking all connections and sensors, restoring factory defaults may resolve the issue.

Turn off the thermostat.
Press and hold the Power button and the Up arrow button simultaneously for 5 seconds.
The display will flash, confirming that factory settings have been restored.

After resetting, reconfigure the basic parameters (temperature setpoint, mode, etc.) and check whether the error code has cleared.

When to Contact Technical Support

If you have completed all the steps above and the error code remains, the issue may be:

A faulty control board
A damaged internal sensor that requires factory replacement
A compatibility issue with the connected heating system

In these cases, please contact our technical support team with the error code displayed and a description of the steps you have already taken.

How to Fix Common Faults on 8818H Thermostats – A Quick Guide for Installers

Common Error Codes: E1, E2, and Err

Step 1: Check and Reset the Thermostat