Solar Panel Not Working? How to Diagnose the Problem

A solar system that has stopped completely is a different problem from one that is merely producing less than it used to, and it is worth knowing which you have before you do anything else. Zero is a binary fault. Something in the chain between the panels and your consumer unit has broken, tripped or shut down, and there is a single break to find.

A fair proportion of dead systems are back up within ten minutes, because the cause is a switch somebody knocked or an inverter that has not reconnected after a power cut. The rest usually need an engineer, and the most common single culprit is the most expensive component you own. Work through the checks below in order.

In summary: If your solar system is showing zero, check the AC and DC isolators and your consumer unit first, then read the inverter display and note any code. A one-off reset that holds means it was a nuisance trip. A red light, a recurring code, or a breaker that trips straight back needs an engineer. Do not keep resetting it.

Is it actually zero, or just producing less?

Establish this before anything else, because the two point at completely different causes. Zero output with a blank or red inverter display means a broken connection or a shut-down inverter. Reduced output with a normal green light means soiling, shading, or a single underperforming string. If your system is still running but the figures have slipped, this is not the right article and you will get further with our guide to solar panels not generating enough power.

Open your monitoring app and look at the shape of the line rather than today's number. A clean cliff-edge to zero on a specific date points to a trip or a failure you can date, which is genuinely useful information for whoever attends. A line that has sagged gradually over months points at dirt, a tree that grew, or an ageing inverter.

One caveat worth stating plainly. On a dark December afternoon a perfectly healthy system also reads zero, and low figures on a grey February day may be the system behaving exactly as it should. Check in daylight, ideally around midday, before concluding anything.

What can I safely check myself in ten minutes?

Five checks, in this order. All of them are look-and-listen. One rule overrides everything below, and it is not a formality: never open the inverter casing, and never touch DC cables or connectors. A solar array generates DC voltage whenever there is light on it. It does not stop being live because you have switched something off or because the grid is down. The Health and Safety Executive is clear that electrical work should only be carried out by qualified people, and this is why.

Check it is daylight and the array is not covered. Occasionally that is the whole answer. Snow, a fallen branch or a sheet left by a roofer will all produce a genuine zero.

Read the inverter display and write down exactly what it says. Note the colour of the status light and copy any code word for word. That single line frequently tells an engineer the cause before they leave the yard, and it is the most useful thing you can do in this list.

Check the isolators. Solar systems have an AC isolator and a DC isolator, usually near the inverter, sometimes near the meter. If one has been knocked off, that alone produces zero.

Check your consumer unit. Look for a tripped breaker or RCD on the solar circuit. Reset it once. If it holds, you are done. If it trips straight back, stop. That is a real electrical fault and repeating it will not help.

Check whether there has been a power cut. Many inverters will not reconnect until the mains has been stable for several minutes, and some need switching off and on at the AC isolator. Give it fifteen minutes before deciding it is dead.

If all five come back clear and the system still shows zero, the fault is beyond what you can safely reach.

What do the inverter lights and error codes mean?

Most UK inverters use a traffic-light scheme. Green means generating, amber or orange generally means standby or a warning, and red means a fault the unit could not clear by itself. The specific code matters more than the colour, and every manufacturer numbers them differently.

A steady green light while your app shows zero usually means the monitoring link has dropped rather than the system. A completely blank display normally means no AC supply is reaching the unit, or the inverter has failed. A grid fault message means the mains has drifted outside permitted limits, and it generally clears itself. A red light with a code that keeps returning is the one that needs an engineer.

To find the exact code, check the manufacturer's app rather than squinting at the display. SolisCloud, mySolarEdge, SEMS and FusionSolar all surface the current fault plainly, and most keep a history, which is often more revealing than the present state. A system that has thrown the same code intermittently for four months is telling you something a single snapshot will not. Our complete UK inverter troubleshooting guide goes through the common codes in detail.

What is an isolation or Riso fault, and is it serious?

An isolation fault means the inverter has measured the insulation resistance between the DC system and earth and found it below the safe threshold, typically under 1 megohm. In plain terms, current is finding a path it should not have. It is a safety fault rather than a performance one.

The usual cause is moisture. One damp connector, one nicked cable, or one junction box with a failed seal anywhere across the array is enough to pull the whole system below the threshold. Corroded connectors do it too, and corrosion also introduces resistance that makes the connector heat up, which is its own hazard.

These faults have a recognisable rhythm. They appear on damp mornings, clear as the day warms and the array dries, then return with the next dew. That pattern makes them easy to dismiss, because the system appears to fix itself. Please do not dismiss it. A fault that keeps clearing is still a fault, and the underlying damage gets worse rather than better.

The key takeaway: a fault that clears itself once is usually the grid. A fault that clears itself repeatedly, on a pattern, is usually moisture on the DC side and needs looking at. Those two get confused constantly, and only one of them is safe to leave.

Why has it stopped after a power cut or a storm?

Grid disturbance is one of the most common reasons a healthy system goes dark, and most of the time it recovers on its own. Inverters are required to disconnect when the mains goes outside permitted voltage or frequency limits, which is a safety feature protecting anyone working on the network.

Persistent grid faults on sunny afternoons are a different animal. If your local network already sits near the top of its voltage range, common at the end of rural lines and in streets where a lot of neighbours have solar, your inverter may trip off precisely when it should be generating most. That is not your system misbehaving, and your Distribution Network Operator can often adjust it.

After a storm, add a ground-level look at the array before assuming it is electrical. Debris impact, a lifted panel or a cable pulled loose by wind will all present as a dead system. Photograph anything you find before it is touched, because insurers ask. Our guide to protecting solar panels from extreme winter weather covers what to check and when.

Is my inverter dead?

On a system more than ten years old with clear isolators and a blank or red display, the inverter is the most likely single answer. It is the hardest-working component in the system and the shortest-lived. Panels are warrantied around 25 years. A string inverter typically lasts 10 to 15, with manufacturer cover usually running out at 10 or 12.

The timing matters right now because of when Britain installed its solar. The Feed-in Tariff boom ran from roughly 2011 to 2015, and the scheme closed to new applicants on 1 April 2019. Systems fitted at the peak of that boom are now eleven to fifteen years old, which is precisely the window in which inverters fail. String inverters, the standard fit on UK homes before around 2018, are particularly exposed because the whole system depends on one unit.

Replacement runs roughly £700 to £1,500 installed for a typical domestic string inverter. Before agreeing to one, it is worth asking whether the unit is genuinely dead or has failed on something repairable, and whether it is still within manufacturer warranty. The serial number and install date settle both questions. Our cost-benefit analysis on replacing an old inverter walks through the decision.

Could it be the monitoring rather than the system?

More often than you would expect. If the inverter display shows a steady green light and a sensible generation figure while your app shows a flat line at zero, your panels are fine and the data link has fallen over. Nothing is broken on the roof.

The causes are mundane. A router was replaced and the Wi-Fi password changed. The monitoring dongle lost its connection or its power. The manufacturer's portal had an outage. A firmware update failed part way through. This is worth ruling out before you book anyone, because it is the one item on this list you can fix yourself with no risk. Walk to the inverter, look at the display, and compare it with the app. If they disagree, believe the inverter.

What about wiring, connectors and rodent damage?

Wiring faults are less common than inverter failures but they are the ones you must not investigate yourself. It is still useful to understand what goes wrong, because it shapes what you tell the engineer.

MC4 connectors, the plug-in connectors joining panel strings together, corrode or work loose over time. That happens faster in damp and coastal conditions, which covers a great deal of Dorset, Hampshire and the Bristol Channel coast alike. Salt air accelerates it considerably. Squirrels and rats chew through DC cabling under roof tiles, producing intermittent faults that are notoriously hard to trace. Junction box failures on the back of individual panels are another possibility, particularly on systems ten years old or more.

Locating any of these needs test equipment and training. Insulation resistance testing across the array, torque-checking terminations and reading the inverter's historical fault log are all part of our 21-point Solar MOT, which ends in a written report with traffic-light grading across every category.

Am I still being paid while the system is down?

No, and this is the part that turns a technical problem into a financial one. Both the Feed-in Tariff and the Smart Export Guarantee pay on what your system actually generates or exports. A dead system generates nothing, so it earns nothing, and the payments simply stop arriving.

That works in your favour as an early warning. A sudden fall in export income is often the first hard evidence of a fault, and it arrives in your bank account rather than in an app you never open. It is also worth checking that your generation meter is still recording, because a stopped meter costs you money even when the panels are working. Our guide to keeping a legacy Feed-in Tariff system running covers what matters most on older installations.

Put a number on it. A 4kW array generating around 3,400 to 4,000 kWh a year is worth somewhere near £70 to £100 a month across the summer, between bill savings and export income. A system left dead from May to September has quietly cost more than most repairs.

When should I stop and call someone?

Stop at the point where the answer requires opening something or repeating something. Specifically: a breaker that trips straight back after one reset, any isolation or Riso fault, a persistent red light with a code, a blank display with the AC supply confirmed present, or any visible damage to panels or cabling.

Resetting a system repeatedly is the thing to avoid. It rarely helps, and on some units it clears the fault log, which is often the most useful diagnostic record an engineer has. If you have already reset it several times, say so when you book, because it changes what they can work from.

If your system is MCS certified, any repair affecting that certification should be carried out by an MCS-registered engineer, to protect both your warranty position and your eligibility for export payments.

Get it diagnosed properly

If you have worked through the safe checks and the system is still dead, the next step is a proper diagnosis rather than another round of switch-flicking. Our 21-point Solar MOT covers panels, mounting, electrical safety, inverter diagnostics, insulation resistance and real generation against expected output, with a written traffic-light report the same day. If you want to know what that involves before booking, here is what a Solar MOT actually is, and here is what repairs typically cost.

We install and maintain solar across both our regions with our own MCS-certified engineers, and we take on systems fitted by other companies as a matter of routine. Knowing how a system should have been built is most of what tells you what has gone wrong with one that was not.

South Coast (Dorset, Hampshire, Bournemouth, Poole, Christchurch, Southampton): 01202 023069. South Wales (Cardiff, Newport, Swansea): 029 2002 6002. Or book online. Same-week availability, rated 10/10 on Checkatrade, 500+ systems installed and inspected.

Frequently asked questions

Why have my solar panels suddenly stopped generating?

A sudden drop to zero usually means a broken connection rather than failed panels. The most common causes are a tripped AC or DC isolator, an RCD that tripped during a power cut, or an inverter that has shut down on a fault. Check the isolators and consumer unit first, and allow fifteen minutes after any outage.

Can I reset my solar inverter myself?

You can switch it off and on once at the AC isolator, which is what most manufacturers advise after a power cut. Never open the casing and never touch DC cabling. If one reset does not hold, or the breaker trips straight back, stop and book an engineer rather than repeating it.

What does a red light on my solar inverter mean?

Red generally indicates a fault the inverter could not clear on its own. The colour alone is not enough to diagnose it, so record the exact message from the display or the manufacturer's app. The fault history often reveals a pattern that a single reading will not.

Why do my solar panels stop working when it rains?

That pattern usually points to an isolation or Riso fault, meaning moisture has reduced the insulation resistance on the DC side below roughly 1 megohm. It commonly clears as the array dries and returns with the next damp morning. It is a safety fault and should be inspected even though it appears to fix itself.

How do I know if it is the panels or the inverter?

Almost always the inverter. Panels have no moving parts and fail rarely, whereas inverters typically last 10 to 15 years and do the hard work. A blank or red display on a system over ten years old points strongly at the inverter. Panel problems usually cause partial losses rather than total stoppages.

My app shows zero but the inverter looks normal. What now?

Believe the inverter. A steady green light with a sensible figure on the display means the system is generating and the monitoring link has dropped. Check the Wi-Fi, the dongle and whether the manufacturer's portal is down before booking anyone.

Is it safe to inspect my solar panels myself?

Ground-level checks are safe: reviewing monitoring data, checking your consumer unit, and reading the inverter display. Anything involving roof access or electrical components carries real risk. Solar arrays carry live DC voltage during daylight and should only be worked on by a qualified engineer.

How much does it cost to fix a solar system that has stopped working?

Some causes cost nothing, such as a one-off reset or reconnecting monitoring. A diagnostic call-out is typically £80 to £150, connector and cable repairs £100 to £200, and inverter replacement £700 to £1,500 installed. Diagnosis first is what stops people paying for parts they did not need.