SMA Sunnyboy Inverter faults

SMA are widely considered a premium brand of inverter. Their inverters are premium priced too, and for that you can expect quality. However, our experience is that many of the older single phase Sunny Boy models fail at around five years old, often just out of their warranty. Here are some of the most common faults (as shown on the LCD display):

PE conn. missing

This message means that the inverter thinks that something has gone wrong with the a.c. supply. It’s one of the more common error messages on Sunny Boy 3000TL-20, 3600TL-20, 4000TL-20 and 5000TL-20 inverters. Usually there is nothing wrong with the a.c. supply, it’s an internal fault in the inverter. We can get your inverter back up and running with a software fix. If you are too far away to benefit from our call-out service you can send your inverter to us. Click here for more information: SMA Sunny Boy TL-20 PE Connect software fix

Varistor defective

This message means that the inverter has detected a component failure. Varistors are sacrificial components that protect the inverter from overvoltages. They wear out with age and in an SMA inverter they are designed to be replaceable. SMA list replacement varistor kits for your their inverters but seemingly no UK supplier wants to stock such low value items. SMA varistors are simply a combination of two standard electronic components and it is possible to cheaply make compatible replacements.

However, this error message can also mean that the inverter just thinks that the varistors are faulty, whereas in fact the fault is with the inverter itself. If your inverter is displaying this error message then there is a chance that replacing the varistors will solve the issue.  However, if the inverter is old enough to be out of warranty then it’s likely that other components are also probably on their way out. Our advice is not to throw any money at it; you are better off replacing the inverter and starting afresh with a ten year warranty.

Solar PV repair enquiry form

Welcome to our online interactive fault diagnosis tool. Complete the fields below as fully as possible and this interactive tool may provide an instant diagnosis. The more information you provide, the more effective it is and it also prompts you for the information we will need to assist you. If you don't know any answers for sure, please don't guess!
Please select an option. If not known then please choose 'Unknown'. If not listed please choose 'Other'
Your inverter model number and serial number can usually be found on a label on the side or underside of your inverter.
Why do we ask this? Certain companies made consistently the same mistakes/short cuts with their installations and this often gives us a clue as to what might be wrong.
If it's around 5 years, is it over or under? This is important as most inverter warranties are 5 years.
A picture speaks a thousand words! If you have any photos or other documents that can help us understand your installation then please upload them here. Particularly useful are photos of the inverter model number sticker, the connections into the inverter and an overall picture of the inverter area showing all isolators etc. You can also email us at
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I acknowledge that RED Electrical normally offers call-out services within a reasonable travelling distance of Chorley, Lancashire and further distances are discretionary and subject to additional charges.