---
title: How to Run a Multimeter Test for Modbus Connection Checks
description: If you are receiving errors in your Installer app that your Modbus system isn’t communicating as expected, you can confirm whether the installation is correct by performing a multimeter resistance check
---
[Skip to content](https://help.homelyenergy.com/knowledge/how-to-run-a-multimeter-test-for-modbus-connection-checks#main-content)
- [English](https://help.homelyenergy.com/knowledge/how-to-run-a-multimeter-test-for-modbus-connection-checks)
- [Lietuvių](https://help.homelyenergy.com/lt/knowledge/kaip-atlikti-multimetrinį-modbus-jungties-testą)
- [Nederlands - Nederland](https://help.homelyenergy.com/nl-nl/knowledge/how-to-run-a-multimeter-test-for-modbus-connection-checks)
English
Show submenu for translations
[Contact us](https://help.homelyenergy.com/knowledge/kb-tickets/new?hsLang=en)
[![Homely logo white.png\]](https://help.homelyenergy.com/hs-fs/hubfs/Homely%20logo%20white.png?height=40&name=Homely%20logo%20white.png)](https://help.homelyenergy.com/knowledge?hsLang=en)
Open main navigation
Close main navigation
- - [English](https://help.homelyenergy.com/knowledge/how-to-run-a-multimeter-test-for-modbus-connection-checks)
- [Lietuvių](https://help.homelyenergy.com/lt/knowledge/kaip-atlikti-multimetrinį-modbus-jungties-testą)
- [Nederlands - Nederland](https://help.homelyenergy.com/nl-nl/knowledge/how-to-run-a-multimeter-test-for-modbus-connection-checks)
English
Show submenu for translations
- [Contact us](https://help.homelyenergy.com/knowledge/kb-tickets/new)
How can we help?
- There are no suggestions because the search field is empty.
1. [Knowledge base](https://help.homelyenergy.com/knowledge?hsLang=en)
2. [Installer Troubleshooting](https://help.homelyenergy.com/knowledge/installer-troubleshooting?hsLang=en)
3. [Homely](https://help.homelyenergy.com/knowledge/installer-troubleshooting?hsLang=en#homely)
# How to Run a Multimeter Test for Modbus Connection Checks
#### **Overview**
If you are receiving errors in your Installer app that your Modbus system isn’t communicating as expected, you can confirm whether the installation is correct by performing a **multimeter resistance check**.
This simple test helps identify wiring issues, missing resistors, or other connection faults.
#### **Step-by-Step Instructions**
1. **Power Off the System**
Ensure the entire Modbus system is powered down before testing. You should ensure the following elements are powered off
1. The heat pump
2. The Homely Hub
3. Any additional Modbus adaptors e.g. DCOM board
This prevents inaccurate readings and protects your equipment.
2. **Verify Connections**
Confirm that all Modbus devices are connected correctly and that the communication wiring is complete.
3. **Set the Multimeter**
Switch your multimeter to its **lowest resistance (ohms) measuring range**.
4. **Measure Across the Bus at both ends of the Connection**
Place the multimeter probes on either side of the **120-ohm terminating resistor** on the Modbus network.
#### **Understanding the Results**
After taking your measurement, compare your multimeter reading against the expected range:
| **Resistance Reading (Ohms)** | **Meaning** | **Recommended Action** |
| --- | --- | --- |
| **40–70 Ω** | ✅ Correct installation | No action needed |
| **0–20 Ω** | ⚠️ Wiring short detected | Inspect cabling and connectors for shorts |
| **20–40 Ω** | ⚠️ Possible power interference | Turn off power to electricity meters and retest |
| **70–130 Ω** | ⚠️ Missing or incorrect termination | Check that the **120-ohm resistor** is correctly installed |
| **130+ Ω** | ⚠️ Broken cable or missing resistors | Check all Modbus cables and terminators |
**Advanced Check: Isolating the Fault**
If the system still shows communication errors, test with the **Modbus cable disconnected** between the heat pump and the Homely Hub:
- If both ends read **around 120 Ω**, each resistor is present and the cable may be **broken**.
- If the **heat pump side** now reads **greater than 120 Ω** (or *OL* for open loop), the **resistor on the heat pump** is likely faulty.
This test helps identify whether the issue lies with the cable or the termination resistor.
#### **When to Contact Support**
If your reading remains outside the expected range after performing the checks above, please **contact Homely Support** for further assistance.
- [Getting Started](https://help.homelyenergy.com/knowledge/getting-started?hsLang=en#main-content)
- [Your Homely System](https://help.homelyenergy.com/knowledge/getting-started?hsLang=en#your-homely-system)
- [Before you buy](https://help.homelyenergy.com/knowledge/getting-started?hsLang=en#before-you-buy)
- [Benefits of Homely](https://help.homelyenergy.com/knowledge/getting-started?hsLang=en#benefits-of-homely)
- [Heat Pump Functions](https://help.homelyenergy.com/knowledge/getting-started?hsLang=en#heat-pump-functions)
- [Using Homely](https://help.homelyenergy.com/knowledge/using-homely?hsLang=en#main-content)
- [Setting up your Preferences](https://help.homelyenergy.com/knowledge/using-homely?hsLang=en#setting-up-your-preferences)
- [Smart+ Features](https://help.homelyenergy.com/knowledge/using-homely?hsLang=en#smart-features)
- [Account Management](https://help.homelyenergy.com/knowledge/using-homely?hsLang=en#account-management)
- [Usage Data](https://help.homelyenergy.com/knowledge/using-homely?hsLang=en#usage-data)
- [Solar Sense](https://help.homelyenergy.com/knowledge/using-homely?hsLang=en#solar-sense)
- [Homeowner Troubleshooting](https://help.homelyenergy.com/knowledge/homeowner-troubleshooting?hsLang=en#main-content)
- [FAQs](https://help.homelyenergy.com/knowledge/homeowner-troubleshooting?hsLang=en#faqs)
- [Hardware](https://help.homelyenergy.com/knowledge/homeowner-troubleshooting?hsLang=en#hardware)
- [Switching to Heat Pump Controller](https://help.homelyenergy.com/knowledge/homeowner-troubleshooting?hsLang=en#switching-to-heat-pump-controller)
- [Heat Pump Errors](https://help.homelyenergy.com/knowledge/homeowner-troubleshooting?hsLang=en#heat-pump-errors)
- [Installer Resources](https://help.homelyenergy.com/knowledge/installer-resources?hsLang=en#main-content)
- [Why Homely](https://help.homelyenergy.com/knowledge/installer-resources?hsLang=en#why-homely)
- [Configuring Homely](https://help.homelyenergy.com/knowledge/installer-resources?hsLang=en#configuring-homely)
- [Compatibility and System Design](https://help.homelyenergy.com/knowledge/installer-resources?hsLang=en#compatibility-and-system-design)
- [Manuals](https://help.homelyenergy.com/knowledge/installer-resources?hsLang=en#manuals)
- [Connect](https://help.homelyenergy.com/knowledge/connect?hsLang=en#main-content)
- [About Connect](https://help.homelyenergy.com/knowledge/connect?hsLang=en#about-connect)
- [Managing Installations](https://help.homelyenergy.com/knowledge/connect?hsLang=en#managing-installations)
- [Installer Troubleshooting](https://help.homelyenergy.com/knowledge/installer-troubleshooting?hsLang=en#main-content)
- [Homely](https://help.homelyenergy.com/knowledge/installer-troubleshooting?hsLang=en#homely)
- [Troubleshooting with Connect](https://help.homelyenergy.com/knowledge/installer-troubleshooting?hsLang=en#troubleshooting-with-connect)
- [Samsung](https://help.homelyenergy.com/knowledge/installer-troubleshooting?hsLang=en#samsung)
[](https://www.homelyenergy.com)
www.homelyenergy.com
Copyright © 2026, Homely