--- title: High Level Switch – Initial Troubleshooting description: Initial troubleshooting guide for High Level Switch alarms and overflow incidents on LiqTech filtration systems. Covers switch verification, wiring checks, alarm severity, unintended inflow paths, and common process-related root causes. --- [Skip to content](https://www.go.liqtech.com/knowledgebase-quickguides/high-level-switch-initial-troubleshooting#main-content) English Show submenu for translations ![](https://www.go.liqtech.com/hs-fs/hubfs/LiqTech_Holding_Black.png?width=1454&height=272&name=LiqTech_Holding_Black.png) - Home - Products - Pricing - Blog - Company Open main navigation Close main navigation - Home - Products - Pricing - Blog - Company - English Show submenu for translations - Contact us Contact us How can we help you? - There are no suggestions because the search field is empty. 1. [LiqTech Service Knowledge Base and Quick Guides](https://www.go.liqtech.com/knowledgebase-quickguides?hsLang=en) 2. [Troubleshooting](https://www.go.liqtech.com/knowledgebase-quickguides/troubleshooting?hsLang=en) 3. [switches](https://www.go.liqtech.com/knowledgebase-quickguides/troubleshooting?hsLang=en#switches) # High Level Switch – Initial Troubleshooting ## This guide describes a systematic, field-proven approach for troubleshooting High Level Switch alarms and overflow incidents on LiqTech filtration systems. It applies to digital high-level switches installed on process tanks such as permeate, backwash, feed, and similar tanks. #### When to use this guide Use this guide when: - A **High Level Switch** alarm is active on the HMI - The system has stopped due to a **high tank level safety condition** - The customer reports an **overflow** or near-overflow situation - The alarm persists even though the tank is expected to be below high level --- #### Preconditions and safety Before starting troubleshooting: - The system should normally be in **STOP state** - Live testing may be required to observe switch behavior - Electrical troubleshooting shall only be performed by personnel with relevant electrical competence - Always follow site-specific safety procedures --- #### Objective of this troubleshooting The objective of this guide is to verify that: - the **High Level Switch can be physically activated**, - the **HMI correctly indicates the activation**, and - the **alarm is configured as a Critical / Stop alarm**, not merely a Warning. In practical terms, it must be possible to: > apply water to the switch → see the HMI indication change → trigger a **critical alarm** → and stop the system. If this chain does not work as expected, the system **cannot be considered protected against overflow**. Alarm severity can be verified directly in the **Alarm Settings** on the HMI. --- #### Important principle A **High Level Switch alarm must always be treated as a real alarm until proven otherwise**. Likewise, a **tank overflow without a corresponding High Level Switch stop** must always be treated as a **critical finding**. The first objective is **not** to explain the process, but to confirm whether: - the switch is physically activated, **or** - the alarm (or missing alarm) is caused by hardware, wiring, or configuration issues. --- #### Step-by-step troubleshooting procedure ### 1. Confirm switch activation using HMI and local indication - Observe the High Level Switch status on the **HMI** - Check the switch for local status indication (LED if present) - Inspect the switch area for fouling, buildup, or foam **Outcome** - Switch appears active → proceed with **process-related troubleshooting** - Switch does not appear active → proceed with **hardware-related troubleshooting** --- ### 2. Hardware-related troubleshooting *(false activation OR missing activation during overflow)* #### 2.1 Manual functional test of the switch - Manually activate the switch using water or a wet cloth - Verify that: - the switch changes state locally - the HMI input changes accordingly --- #### 2.2 Verify the complete signal path (end-to-end) The entire signal path must be verified: - Switch element - Switch hat / connector - Cable gland - Field cable - Junction box (JB) - Cabinet terminals - Digital input (DI) card Checks to perform: - Measure and/or buzz continuity conductor-by-conductor - Verify correct 24 VDC supply and reference - Inspect terminals for loose connections, corrosion, or incorrect termination **Common field issues** - Incorrect pin assignment - Wiring landed on wrong terminal - Broken conductor inside cable - NPN / PNP mismatch - Incorrect DI channel --- #### 2.3 Verify alarm behavior and severity on HMI - Confirm the High Level Switch alarm is configured as **Critical / Stop** - Verify it is **not configured as Warning only** If an overflow has occurred, verify whether the input ever changed state on the HMI. --- #### 3. Process-related troubleshooting *(correct activation)* ### 3.1 Verify alignment with level transmitter (most common cause) This is **by far the most common root cause**. Verify that: - the level transmitter is correctly scaled, see articel "Level Alarms (Transmitter) - Initial Troubleshooting" - transmitter high-level setpoints are **not set higher than or too close to** the physical switch position --- ### 3.2 Identify all possible inflow paths to the tank Systematically check **all ways liquid can enter the tank**, including unintended paths: - Leakage through permeate FCVs during CIP due to wear or calibration drift - Technical or utility water unintentionally entering the tank - Internal leakage across valves assumed to be closed - Bypass lines or drain returns routed back to the tank Small continuous inflows can raise the tank level over time. --- ### 3.3 Verify downstream conditions - Confirm downstream valves are open as intended - Check for blocked or closed outlets - Verify correct routing and active tank selection on the HMI --- ### 3.4 Check flow balance and control behavior (PID) - Upstream pump control may be too aggressive - Downstream pump may be too slow or stopped - Ramp-up behavior may cause temporary overfilling ⚠️ **Important** If PID or control behavior is suspected to be the root cause, **LiqTech must be contacted**. PID parameters and control philosophy are **not intended to be modified during field troubleshooting**. --- ### 3.5 Marine installations (if applicable) On vessels, **sloshing due to sea state** can cause intermittent activation of high-level switches even when average level appears acceptable. --- #### Common root causes ### Hardware-related - Fouled or contaminated switch - Switch mechanically unable to activate - Incorrect wiring or termination - NPN / PNP mismatch - Faulty digital input channel - Alarm configured as Warning instead of Critical ### Process-related (most common) - **Incorrect level transmitter scaling** - **High-level setpoint on transmitter misaligned with physical switch** - Unintended inflow to the tank - Incorrect valve or pump state - Aggressive or unstable control behavior - Sloshing in marine installations from ship rolling --- #### When to stop and contact LiqTech Service - If switch behavior cannot be verified locally - If continuity and wiring are verified end-to-end but alarm behavior is incorrect - If PID or control behavior is suspected - If an overflow occurred without High Level Switch intervention and the root cause cannot be clearly identified --- #### Alarm ID examples (for agent guidance) The following alarm IDs are non-exhaustive **examples** of **High Level Switch** alarms observed in LiqTech systems. They are provided to help support agents **recognize the alarm type** when a customer references an alarm number. **Other High Level Switch alarm IDs may exist** depending on system type and project. - **MK6 Generic:** Alarm ID **51** – *Permeate High Level Switch* - **Project-specific systems (e.g. KOC3000):** Additional High Level Switch alarms may exist for other tanks (e.g. feed, neutralization, process tanks). Alarm IDs vary by project and should be confirmed in the relevant alarm list. - [Troubleshooting](https://www.go.liqtech.com/knowledgebase-quickguides/troubleshooting?hsLang=en#main-content) - [FCV](https://www.go.liqtech.com/knowledgebase-quickguides/troubleshooting?hsLang=en#fcv) - [Transmitters](https://www.go.liqtech.com/knowledgebase-quickguides/troubleshooting?hsLang=en#transmitters) - [valves](https://www.go.liqtech.com/knowledgebase-quickguides/troubleshooting?hsLang=en#valves) - [Pump](https://www.go.liqtech.com/knowledgebase-quickguides/troubleshooting?hsLang=en#pump) - [IO](https://www.go.liqtech.com/knowledgebase-quickguides/troubleshooting?hsLang=en#io) - [switches](https://www.go.liqtech.com/knowledgebase-quickguides/troubleshooting?hsLang=en#switches) - [Permeate](https://www.go.liqtech.com/knowledgebase-quickguides/troubleshooting?hsLang=en#permeate) - [FAQs](https://www.go.liqtech.com/knowledgebase-quickguides/faqs?hsLang=en#main-content) - [CIP](https://www.go.liqtech.com/knowledgebase-quickguides/faqs?hsLang=en#cip) - [Alarm](https://www.go.liqtech.com/knowledgebase-quickguides/faqs?hsLang=en#alarm) - [Support](https://www.go.liqtech.com/knowledgebase-quickguides/support?hsLang=en#main-content) - [Performance](https://www.go.liqtech.com/knowledgebase-quickguides/support?hsLang=en#performance) - [Pool](https://www.go.liqtech.com/knowledgebase-quickguides/pool?hsLang=en#main-content) - [Trouble Shooting](https://www.go.liqtech.com/knowledgebase-quickguides/pool?hsLang=en#trouble-shooting) - [Operation & Maintenance](https://www.go.liqtech.com/knowledgebase-quickguides/pool?hsLang=en#operation-maintenance) - [Crossflow](https://www.go.liqtech.com/knowledgebase-quickguides/crossflow?hsLang=en#main-content) - [Trouble Shooting](https://www.go.liqtech.com/knowledgebase-quickguides/crossflow?hsLang=en#trouble-shooting) - Home - Products - Pricing - Blog - Company [mailto:email@email.com](mailto:email@email.com) Copyright © 2026, LiqTech