Building Salesforce Flow is easier than ever, but even experienced admins eventually run into an error that stops an automation from working. One of the most common messages you’ll see is:

“An unhandled fault has occurred in this flow.”

Unfortunately, this message doesn’t explain what actually went wrong. It simply tells you that Salesforce encountered an error while executing your Flow.

The good news is that almost every Flow error can be identified and fixed if you know where to look. Salesforce provides several debugging tools, including the Flow Debugger, Debug Logs, Fault Paths, and detailed Flow error emails. Learning how to use these tools will save hours of troubleshooting and help you build more reliable automation.

In this guide, you’ll learn how to debug Salesforce Flow errors step by step, understand the most common causes of failures, and apply best practices to prevent them in the future.

Why Do Salesforce Flows Fail?

A Flow can fail for many reasons. Sometimes the problem is in your logic, while other times it’s related to permissions, missing data, validation rules, or governor limits.

Some of the most common Flow errors include:

• An unhandled fault has occurred in this flow.
• FIELD_CUSTOM_VALIDATION_EXCEPTION
• INSUFFICIENT_ACCESS_OR_READONLY
• Required field missing
• Record not found
• Null value errors
• Duplicate record errors

Instead of guessing the cause, Salesforce provides several ways to identify exactly where the failure occurred. If your Flow also uses multiple collections and loops, following Salesforce Flow Loops: Collections, Iteration, and Best Practices can help eliminate many performance-related issues before they become errors.

Understanding “An Unhandled Fault Has Occurred in This Flow”

This error appears when Salesforce encounters a problem but your Flow doesn’t have a Fault Path to handle it.

Instead of displaying a meaningful message, Salesforce stops the Flow and shows a generic error.

For example:

• Update Records fails because of a validation rule.
• Create Records fails because a required field is empty.
• User doesn’t have permission to update a record.
• Apex Action throws an exception.

Without a Fault Path, every one of these situations produces the same generic error.

That’s why adding Fault Paths should become a standard part of every Flow you build.

What Is a Fault Path?

A Fault Path is the red connector available on data elements such as:

• Get Records
• Create Records
• Update Records
• Delete Records
• Apex Actions
• Subflows

Whenever one of these elements fails, Salesforce follows the Fault Path instead of terminating the Flow immediately.

Using Fault Paths allows you to:

• Display user-friendly error messages.
• Log errors into a custom object.
• Send notification emails.
• Create support cases automatically.
• Continue troubleshooting more easily.

Step 1: Use Flow Builder Debug Mode

The easiest way to troubleshoot a Flow is by using the built-in Debug button.

Open your Flow in Flow Builder and click Debug.

Depending on the Flow type, Salesforce lets you configure options such as:

• Input variables
• Record ID
• Run as another user
• Rollback mode
• Skip entry conditions

Rollback mode is especially useful because Salesforce executes the Flow without permanently changing any data.

After clicking Run, Salesforce executes every element one by one while showing exactly what happened.

You’ll see:

• Which path was selected.
• Decision outcomes.
• Variable values.
• Assignment results.
• Record updates.
• Error messages.

This makes Debug Mode the fastest way to locate incorrect Flow logic before deploying changes. Salesforce has continued improving the Debug Panel in recent releases, making it easier to inspect execution paths and variable values.

Reading the Debug Output

Many admins only look for the red error message.

Instead, examine the entire execution path.

Ask yourself:

• Did the Flow start correctly?
• Did Get Records return any records?
• Was the expected Decision outcome selected?
• Did Assignment change the correct values?
• Which element failed?

Following the Flow from top to bottom usually reveals the problem within a few minutes.

Image Prompt (Place Here)

Step 2: Check Flow Error Emails

Whenever an active Flow fails, Salesforce automatically sends an error email to the Flow owner or the last person who modified the Flow.

These emails often contain valuable information such as:

• Flow name
• Flow version
• User who triggered the Flow
• Failed element
• Error message
• Record ID

Instead of immediately opening Flow Builder, start by reading the email carefully.

In many cases, Salesforce already tells you exactly which element caused the failure.

Step 3: Review Debug Logs

Some problems don’t appear clearly inside Debug Mode.

This is where Salesforce Debug Logs become useful.

Debug Logs capture:

• Flow execution
• Database operations
• Variable assignments
• Apex execution
• Validation rules
• Permission failures

To enable them:

1. Go to Setup.
2. Search for Debug Logs.
3. Add your user.
4. Set Workflow log level to Fine or higher.
5. Reproduce the issue.
6. Review the generated log.

The log shows every Flow element executed and helps identify hidden issues that aren’t obvious from the Flow canvas.

As your automations become more advanced, combining proper debugging with clean branching logic makes troubleshooting much easier. If your Flows contain multiple decisions, Salesforce Flow Loops: Collections, Iteration, and Best Practices is a helpful companion guide.

Step 4: Check Field-Level Security and User Permissions

Sometimes your Flow works perfectly during testing but fails for end users.

The reason is often Field-Level Security (FLS) or object permissions.

For example, your Flow may try to update a field that the running user cannot edit.

Common permission-related errors include:

• INSUFFICIENT_ACCESS_OR_READONLY
• Insufficient privileges
• Field is not writable
• Record access denied

If your Flow runs as the current user, always verify:

• Object permissions
• Field-Level Security
• Record ownership
• Sharing Rules
• Permission Sets

Testing the Flow as another user in Debug Mode is one of the quickest ways to identify permission issues.

Step 5: Check Validation Rules

Validation Rules are another common reason why Flows fail.

Imagine your Flow updates an Opportunity, but a Validation Rule requires the Close Date to be populated.

The Update Records element fails immediately.

Instead of assuming your Flow is broken, check whether any Validation Rules prevent the update.

Ask yourself:

• Is a required field missing?
• Did another automation change the record?
• Has a Validation Rule recently been added?
• Is the record meeting all business requirements?

Many Flow errors originate outside the Flow itself.

Step 6: Verify Get Records Results

A surprising number of Flow failures happen because Get Records returns nothing.

For example:

Your Flow expects to retrieve a Contact.

Instead:

Get Records returns 0 records.

The next Assignment or Update element attempts to use a record that doesn’t exist, resulting in a null value error.

Always verify:

• Was the correct filter used?
• Did the query return any records?
• Is the record active?
• Was the Record ID passed correctly?

The Debug Panel clearly shows how many records were retrieved, making this problem easy to identify.

Step 7: Watch for Governor Limits

Although Flow requires no code, Salesforce governor limits still apply.

Large Flows may fail because they exceed limits such as:

• Too many SOQL queries
• Too many DML operations
• CPU timeout
• Too many executed elements

This usually happens when admins:

• Update records inside Loops
• Create records inside Loops
• Retrieve unnecessary data
• Build deeply nested logic

If your automation contains collections, revisit Salesforce Flow Loops: Collections, Iteration, and Best Practices ensure records are processed efficiently instead of one by one.

Common Salesforce Flow Mistakes

The following mistakes cause most production Flow failures.

Missing Fault Paths

Without Fault Paths, users only see a generic error instead of meaningful information.

Updating Records Inside Loops

This increases DML operations and may hit governor limits.

Hardcoded Record IDs

Record IDs differ between Sandbox and Production.

Always retrieve records dynamically.

Ignoring Null Values

Always verify that variables contain data before referencing them.

Not Testing Different Scenarios

A Flow should be tested with:

• Valid records
• Invalid records
• Missing values
• Different user profiles
• Large datasets

Testing only the “happy path” often leaves hidden issues undiscovered.

Real Troubleshooting Example

Suppose a Record-Triggered Flow updates every related Contact whenever an Account becomes Active.

The Flow suddenly starts failing.

Instead of guessing:

1. Run Debug Mode.
2. Check Get Records.
3. Verify Contacts were retrieved.
4. Inspect Assignment values.
5. Review Update Records.
6. Open Debug Logs.
7. Read the Flow Error Email.

You discover a new Validation Rule requires the Department field before Contacts can be updated.

The Flow logic was correct.

The Validation Rule caused the failure.

This structured approach is much faster than randomly editing Flow elements.

Best Practices for Error-Free Salesforce Flows

Before activating any Flow, verify the following checklist:

• Add Fault Paths wherever possible.
• Test using Debug Mode.
• Run in Rollback Mode during testing.
• Test with different users.
• Review Flow Error Emails.
• Check Debug Logs for complex issues.
• Avoid DML inside Loops.
• Retrieve only required records.
• Test with realistic production-like data.
• Document complex automation logic.

Following these practices significantly reduces unexpected production failures.

If you’re testing new automations, using the correct environment is equally important. Salesforce Sandbox Types Explained: Developer, Developer Pro, Partial Copy, and Full explains which Sandbox type is best suited for Flow development and testing before deployment.

Frequently Asked Questions

Why does Salesforce show “An unhandled fault has occurred in this flow”?

This message appears when a Flow encounters an error but doesn’t have a Fault Path to handle it. The actual cause may be a validation rule, missing data, permission issue, or failed update.

What is the best way to debug a Salesforce Flow?

Start with Flow Builder Debug Mode. If the issue isn’t obvious, review Flow Error Emails and Debug Logs for additional details.

What are Fault Paths in Salesforce Flow?

Fault Paths are error-handling connectors that execute whenever a Flow element fails. They allow you to display friendly messages or log errors instead of showing generic Flow failures.

Can Debug Mode change my Salesforce data?

Yes, unless you enable Rollback Mode. Rollback Mode executes the Flow without permanently saving database changes.

Why does my Flow work for Admins but not for other users?

Most often this happens because of object permissions, Field-Level Security, sharing rules, or missing Permission Sets.

Final Thoughts

Salesforce Flow debugging isn’t about fixing random errors—it’s about following a consistent troubleshooting process. By using the Flow Debugger, Debug Logs, Flow Error Emails, and Fault Paths together, you can quickly identify the root cause of failures instead of relying on trial and error.

The most valuable habit you can develop is adding Fault Paths during Flow design rather than after something breaks. Combined with proper testing, bulk-safe automation, and clean Flow architecture, this approach leads to more reliable automations and a better user experience.

Related Articles

• Salesforce Flow Loops: Collections, Iteration, and Best Practices
• Salesforce Flow Loops: Collections, Iteration, and Best Practices
• Salesforce Sandbox Types Explained: Developer, Developer Pro, Partial Copy, and Full
• How to Prevent Recursive Triggers in Salesforce Apex
• Salesforce Field History Tracking vs Setup Audit Trail: Which to Use?