Warning What does this mean?

Your system is down or running degraded, but this is not an immediate safety danger. Work through the safe steps below.

SMA Inverter K1 Open Error — Does the Inverter Need Replacing?

The 'K1 Open' message means your SMA inverter's self-test found a problem with its grid relays — the internal switches (K1, and on some models K2) that connect the inverter to the grid. For safety, the inverter will not connect to the grid until the relays check out. This is an internal hardware fault that usually ends with the inverter being serviced or replaced, so contact your installer.

What should I do first?

Two quick questions — we'll point you to the right starting point.

Is this code still showing on your inverter's display?

What this code means

Before your SMA inverter connects to the grid each time it starts up, it runs a relay test: it commands the grid relays open and closed and verifies they actually respond. 'K1 Open' — along with its siblings K1-Close, K2-Open, and K2-Close — means that test found a disturbance: a relay that will not open or close properly.

Because those relays are the safety barrier between your DC solar array and the AC grid, the inverter takes no chances. If the relays misbehave, it simply refuses to connect. At first you will see the yellow LED flashing 'Code 5' while the inverter repeats the relay test. If the disturbance keeps occurring, the inverter switches to what SMA calls 'Permanent Disable Mode' — the yellow LED stays on continuously — and waits for service.

This message family appears on long-running Sunny Boy models, and in practice a persistent K1 fault means the relay or its drive circuitry has failed. SMA's official corrective measure is to contact your installer for further investigation — there is no user-serviceable part involved, and the standard resolution is a service exchange or replacement of the unit.

The relay test itself is simple in concept: the inverter's controller commands each grid relay to open and close and reads back position feedback to confirm it obeyed. 'K1 Open' specifically flags the opening side of that check going wrong — the relay did not reach or report the expected state. On models with two grid relays (K1 and K2), you may see any of the four combinations: K1-Open, K1-Close, K2-Open, K2-Close. They all mean the same thing at the homeowner level: the grid-connection safety hardware failed its self-test.

Two details from SMA's official article are worth knowing. First, the inverter does not give up after one failed test — at first, the yellow LED flashes 'Code 5' while it keeps repeating the relay test, because a single bad reading can occasionally be a glitch. Second, if the disturbance keeps occurring, the inverter escalates to 'Permanent Disable Mode,' with the yellow LED continuously illuminated, and stops trying. That escalation is deliberate: a relay that repeatedly fails its test is treated as definitively faulty, and the unit waits for service rather than risking an unverified grid connection.

What is this downtime costing you?

Rough estimate while your system isn't producing. Adjust the numbers to match your setup.

System size (kW) Peak sun hours / day Electricity rate ($/kWh)

–per day

–per week

–per 30 days

≈ – kWh of lost production per day.

Estimate only — assumes ~80% real-world output vs. nameplate. Actual losses depend on weather, shading, panel direction, and your tariff.

Common causes

Worn or welded relay contacts inside the inverter after years of daily switching
Failed relay drive electronics on the inverter's control board
Internal hardware fault in the grid-connection safety circuit
In rare cases, a transient test glitch that clears and never returns
Relay coil failure — the electromagnetic actuator no longer moves the contacts
Control board fault in the relay test or drive circuitry
Corroded or degraded internal connections in the relay circuit after many years of service

Safe steps to try

Work top to bottom, ticking off each step as you complete it. 0 of 5 done.

Note whether the yellow LED is flashing 'Code 5' (still retrying the relay test) or continuously lit (permanent disable), and tell your installer which you see
You may perform one documented full restart of the system; if the message returns, stop there
Check that the message appears during daylight hours when the inverter is attempting to connect — the K1 relay is normally open with no sunlight, and the fault is about a failed connection attempt, not the idle state
Record the inverter's serial number and the exact message text — a photo of the display helps the warranty process
Do not open the inverter or attempt to 'free' the relay; the relays are internal mains-voltage components

Is your inverter still under warranty?

Before paying for a repair, check — your installer may fix this free.

Brand Year installed

Based on typical standard warranty terms — always confirm with your warranty card or installer paperwork, as terms vary by model, region, and purchase date.

When to call an electrician

Contact your solar installer as soon as K1 Open appears during daylight operation. SMA's official guidance for this message is exactly that: the installer investigates, and because the fault is internal to the inverter, the outcome is normally a service exchange or replacement unit rather than a field repair. If your installer is unreachable, contact SMA Service directly with the serial number and a photo of the display. Do not keep power-cycling the unit hoping it clears; repeated relay-test failures are the inverter telling you the hardware is done.

Frequently asked questions

Does K1 Open always mean the inverter is dead?

A persistent K1 Open during sunny hours effectively means the inverter cannot connect to the grid, so yes — the unit needs professional service, which usually means replacement. A one-off occurrence that never repeats can be a transient glitch.

Is it safe to leave the inverter showing K1 Open?

Yes. The message means the safety system is working — the inverter is refusing to connect. It is not producing power, but it is not dangerous either. Just get it serviced.

Can my installer repair the relay instead of replacing the inverter?

No. SMA treats this as a unit-level fault handled through service exchange, not a field repair. The relays are not user-serviceable or installer-serviceable parts.

Will this be covered under warranty?

Often, yes. SMA inverters carry long warranties and a relay fault is a recognized hardware failure. Your installer will start the warranty process with SMA using your serial number and the fault photo.

What is Permanent Disable Mode?

It is the state the inverter enters when the relay disturbance keeps recurring. The yellow LED stays on continuously and the inverter stops attempting to connect to the grid. Only service — in practice, a unit exchange — takes it out of that state.

Need a professional?

This fault may need professional diagnosis. Contact a qualified solar electrician in your area.

Sources: meaning and troubleshooting verified against the manufacturer's documentation — SMA Solar Technology official service article 'Message K1-Open, K2-Open, K1-Close or K2-Close' (my.sma-service.com); Sunny Boy service manual relay-test message table (K1-Open/K1-Close = fault during relay test).