KNX LED Feedback Not Working – Common Mistakes Explained

By /
nl-smarthome-728x90

Introduction

LED feedback on KNX keypads looks simple on the surface:

  • Light ON → LED ON
  • Light OFF → LED OFF

Yet in real projects, LED feedback often behaves strangely:

  • LEDs don’t update
  • LEDs show wrong status
  • LEDs work sometimes, not always
  • LEDs work during testing but fail later

When this happens, the problem is rarely the LED hardware itself.
Almost always, the cause lies in group address logic, feedback design, or ETS configuration mistakes.

This article explains the most common reasons KNX LED feedback does not work, based on patterns seen repeatedly across residential, commercial, and hotel projects.

First Principle: LED Feedback Is a Communication Function

A KNX LED does not “know” the load state by itself.

It depends entirely on:

  • Correct feedback objects
  • Correct group address linking
  • Correct logic flow

If any part of this chain is broken, LED feedback fails — even though the load itself works perfectly.

Mistake 1: Using the Same Group Address for Control and Feedback

This is the most common mistake worldwide.

What Happens

  • Same group address used for switching and feedback
  • LED appears to follow the command, not the real state

Why It Fails

  • KNX is event-based, not state-based
  • Commands do not always reflect actual load state
  • Actuators may change state independently

Correct Practice

  • One group address for control
  • A separate group address for status feedback

LEDs must listen to feedback, not commands.

Mistake 2: Feedback Object Not Linked at All

Very simple, very common.

Typical Scenario

  • Light switches correctly
  • LED never changes
  • ETS programming otherwise looks complete

Root Cause

  • Feedback object exists but is not linked to any group address
  • Or linked to the wrong group address

Fix

  • Identify the correct status object in the actuator
  • Link it to the LED feedback group address
  • Re-download application and filters

Mistake 3: Wrong Feedback Object Selected

Many actuators provide multiple feedback objects:

  • Switching status
  • Forced status
  • Lock status
  • Scene status

What Goes Wrong

  • LED listens to a secondary or special-purpose object
  • Status does not reflect real load state

Fix

  • Use the actual switching status object
  • Avoid using force or lock feedback unless required

Always read object descriptions carefully.

Mistake 4: Feedback Sent but Blocked by Filters

This happens in multi-line or routed systems.

Symptoms

  • LED works on same line
  • Stops working across lines
  • Random behaviour after changes

Root Cause

  • Feedback telegram filtered by line coupler or IP router
  • Filters not regenerated after changes

Fix

  • Rebuild filter tables
  • Download filters to all couplers/routers
  • Verify feedback group address is allowed through

Filtering mistakes make LEDs look “dead” even though logic is correct.

Mistake 5: LED Parameter Mode Set Incorrectly

Most KNX keypads allow different LED behaviours:

  • Follow status
  • Follow object value
  • Inverted logic
  • Flashing modes

Common Error

LED configured to follow the button press, not the feedback object.

Fix

  • Set LED to follow external object
  • Assign correct feedback group address
  • Verify polarity (normal / inverted)

Never assume default LED behaviour is correct.

Mistake 6: Scene Control Without Scene Feedback

Scenes are a special case.

Typical Problem

  • Scene works correctly
  • LED does not reflect scene activation

Why

  • Scene commands do not automatically provide feedback
  • Actuator does not send scene status by default

Fix Options

  • Use scene status objects (if supported)
  • Or derive LED feedback from load status instead of scene status

LEDs should reflect real load state, not scene number.

Mistake 7: Central Logic Overrides Local Feedback

When logic modules or servers are involved:

Symptoms

  • LED updates initially
  • Then changes unexpectedly
  • Or gets stuck

Root Cause

  • Central logic sends commands without updating feedback
  • Feedback loop broken

Fix

  • Ensure logic writes to the same feedback object
  • Avoid parallel logic paths
  • Define one “source of truth” for state

Distributed logic must still respect feedback flow.

Mistake 8: Actuator Does Not Support True Status Feedback

Some basic actuators:

  • Do not provide real-time status
  • Only echo received commands

Result

LED follows commands, not actual output state.

Fix

  • Use actuators with true status objects
  • Or accept limited feedback accuracy

This is a device capability limitation, not a programming error.

Mistake 9: Partial Downloads After Changes

LED feedback issues often appear after:

  • Small ETS changes
  • Parameter-only downloads
  • Interrupted downloads

Effect

  • Keypad updated
  • Actuator not updated
  • Objects mismatched

Fix

  • Perform full application download
  • Re-download filters
  • Restart affected devices if required

Consistency matters.

Mistake 10: Testing Feedback the Wrong Way

Common testing mistake:

  • Pressing button repeatedly
  • Expecting LED to toggle instantly

Correct testing:

  • Change load state externally
  • Observe LED response
  • Test from multiple control points

LED feedback must represent system state, not button activity.

How to Diagnose LED Feedback Issues (Quick Method)

1️⃣ Confirm LED listens to feedback, not control
2️⃣ Verify correct feedback object
3️⃣ Check group address linking
4️⃣ Rebuild and download filters
5️⃣ Check LED parameters
6️⃣ Test load state independently

This sequence resolves most issues quickly.

Why LED Feedback Problems Appear After Handover

Because:

  • Client uses multiple control points
  • Scenes and logic are activated
  • System runs continuously
  • Feedback paths are stressed

Simple demo tests rarely expose feedback design flaws.

Preventive Design Rules

✔ Always separate control and feedback
✔ Name group addresses clearly
✔ Standardise LED behaviour across project
✔ Document feedback logic
✔ Test across lines and scenarios

Good LED feedback design improves user trust instantly.

Conclusion

When KNX LED feedback is not working, the problem is almost never the LED.

It is:

  • A logic issue
  • A feedback design issue
  • A filtering issue
  • Or a misunderstanding of how KNX represents state

Once feedback is designed correctly, LEDs become:

  • Reliable
  • Predictable
  • Consistent across all control points

In KNX systems, good feedback design is the difference between “it works” and “it feels right.”

Related Posts

Scroll to Top