SolarEdge Inverter 18XB7 Error Code: AC Grid Contactor Fault

Quick Answer

SolarEdge 18XB7 means the internal AC relay that physically connects the inverter's output to the grid has malfunctioned. This relay is a safety-critical component - it is what disconnects the inverter from the grid when a fault is detected. When it fails to operate correctly, the inverter cannot safely connect and shuts down.

This relay is a safety-critical component - it is what disconnects the inverter from the grid when a fault is detected. When it fails to operate correctly, the inverter cannot safely connect and shuts down. A power cycle may clear a temporary firmware-triggered fault, but a mechanically failed relay requires board or inverter replacement.

SolaredgeInverterSeverity: highDifficulty: advanced60% DIY Success

Time to Fix

120–480 min

Difficulty

advanced

Parts Cost

$800 – $2500

Tools Needed

SetApp (SolarEdge mobile app)

What Does the 18XB7 Code Mean?

18XB7 is an AC grid contactor (relay) fault. The internal relay that connects the inverter to the grid has failed. Power cycle first. If the code returns, the relay hardware has failed and professional service is required.

Most Likely Causes

Based on aggregated repair data, here is the probability breakdown for this error code:

Relay failure (contact wear or welding)40%

Wiring fault at relay connection24%

Internal hardware failure22%

Firmware issue triggering false fault14%

Symptoms You May Notice

Inverter failed to start up in the morning
LCD shows 18XB7
Inverter may produce a clicking sound on startup attempts
Production dropped to zero suddenly mid-day

Can you reset a Solaredge inverter to clear the 18XB7 code?

Turn off the AC disconnect for 5 minutes and turn it back on. The inverter will run through its startup sequence and attempt to close the AC contactor. If the relay is mechanically failed, this reset will not hold.

Tools Required for Diagnosis

SetApp (SolarEdge mobile app)

Diagnostic Checklist

Follow these steps in order. We start with the easiest external fixes before opening up the machine.

Turn off the AC disconnect, wait 5 minutes, and turn it back on

Turn off the AC disconnect, wait 5 minutes, and turn it back on. Listen for clicking sounds from the inverter during startup - normal relay operation produces a faint click as the contactor closes.

Check SetApp for fault history

Verify inverter warranty status

Ask your installer whether the AC contactor module can be

After repair or replacement, request that the technician verify

Replacement Parts

If your diagnostic testing proves the component has failed, you will need a replacement. We recommend OEM parts over aftermarket for water-handling components.

Part Name	OEM Number	Estimated Price
SolarEdge Replacement InverterSE7600H-US (model-specific) · $800–$2500	SE7600H-US (model-specific)	$800 – $2500

Verify part fitment for your Solaredge model

Repair vs. Replace Calculator

Appliance Age (Years)7 Yrs

Labor Approach

Our Verdict

REPLACE

Estimated Cost: $1650 (Parts) vs $1650 (New Machine)

Frequently Asked Questions

What is the AC grid contactor on a SolarEdge inverter?

The AC contactor is a mechanical relay inside the inverter that physically connects or disconnects the inverter's AC output to the grid. It closes when the inverter starts up and opens when the inverter shuts down or detects a fault. It must operate correctly for the inverter to produce power safely.

Can a surge protector prevent 18XB7 relay failures?

A whole-home or utility-side surge protector can reduce the risk of surge-induced relay failure. However, most 18XB7 failures in older inverters are due to normal contact wear from years of daily switching cycles.

Is 18XB7 more common in older SolarEdge inverters?

Yes. The AC relay is a mechanical component with a rated number of switching cycles. Inverters 8 or more years old that cycle daily are approaching the end of the relay's rated life. Failure rates increase notably past the 10-year mark.

How do I know if 18XB7 is a relay failure versus a firmware issue?

A firmware-triggered 18XB7 typically clears after a power cycle and does not recur. A relay failure either does not clear after a power cycle or recurs within days. If the fault appeared after a firmware update, escalate to SolarEdge support for a firmware rollback or patch.

My inverter shows 18XB7 every morning but clears itself by 9am. Is this serious?

Yes - a relay that fails on cold starts but eventually recovers is showing early-stage failure. The contact resistance is likely elevated when cold and drops to acceptable levels as the inverter warms up. Schedule a service visit before the relay fails completely, while the system still has some production.

Related Solaredge Inverter Error Codes

Code: HUBSolarEdge Inverter Error Codes: Complete Fault Guide for SE Series Code: 18XB5SolarEdge Inverter 18XB5 Error Code: Internal Hardware Fault Code: RESETSolarEdge Inverter Error Codes: Complete Fault Guide for SE Series

Models Known to Experience 18XB7 Errors

This repair applies to most Solaredge inverters with this error code. Common model numbers include:

SE7600H, SE10000H, SE6000H, SE3000H

Last verified for technical accuracy on March 14, 2026