Solar inverter not working: Lahore fault guide

Start with what the inverter is telling you

An inverter that has genuinely failed is rare. Out of roughly 500 installs handled across Lahore in 11 years, the callouts that ended in a replaced inverter sit somewhere around one in nine. The rest were a fuse, an isolator, a loose lug, a grid problem, or a homeowner who flipped the wrong breaker while getting a fan repaired.

So before anything else, look at the unit and note which of these four states it is in. The whole diagnosis branches from here.

• Screen completely blank, no LEDs, no fan noise. Nothing is reaching the inverter. This is a supply problem, not an inverter problem, until proven otherwise.
• Screen on, showing 0W or standby, no fault code. The inverter is alive and has decided not to produce. Usually DC side or a grid parameter.
• Screen on, showing a fault code. The easiest case. The unit has already done the diagnosis for you. Our inverter error codes guide covers the codes seen weekly in Lahore.
• Screen on, producing but far below normal. Not a dead inverter at all. Read why solar output drops in Lahore instead.
• Clicking or relay chatter every few seconds. Grid instability or a failing relay. Note the time of day it happens.

Write down the state, the time, and the weather. A fault that only appears between 1 pm and 4 pm in June is a different animal from one that appears at 7 am in December.

Check one: the DC isolators

Almost every Lahore install has two DC isolators. One sits on the roof near the array in a grey IP65 box, the other is on the wall within arm's reach of the inverter. Both are rotary switches with an OFF and ON position.

The roof isolator is the one that catches people out. Water tank cleaners, dish antenna technicians, and masons doing waterproofing before monsoon all walk past that box. It gets bumped. In Johar Town and Model Town where roof access is shared or where a tenant lives upstairs, this is the single most common cause of a dead-looking system.

Go up, look at the roof box, confirm the handle is at ON. Come down, confirm the indoor isolator is at ON. If the screen wakes up, the job is done and it cost nothing.

When the isolator itself has failed

Cheap DC isolators sold in Lahore fail in a specific way: the contacts pit and carbonise, and the switch reads ON while passing nothing. If the handle is already at ON and the screen is still dead, the isolator is a suspect. A decent replacement rated at 1000V DC costs PKR 3,500 to 6,000 fitted. Do not let anyone fit an AC-rated isolator on the DC side. DC arcs do not self-extinguish and that box will eventually burn. This is a real fire risk, not a sales line.

Check two: fuses and breakers

The DC combiner box holds inline fuses on each string, typically 15A or 20A gPV cartridges. They blow after a lightning-adjacent surge, which Lahore gets in July and August, or after a string short caused by rodents chewing DC cable insulation on the roof. Rat damage on unprotected DC cable is depressingly common in older Gulberg and Mughalpura houses where the roof backs onto trees.

On the AC side, look for the dedicated inverter MCB in your distribution board. It is often a 32A single pole for a 5kW single phase build. If it has tripped, do not simply reset it and walk away. Something tripped it. Reset once, watch the inverter come up, and if it trips again within minutes, stop and call an electrician.

Item	Where it sits	Typical symptom	Replacement cost
gPV DC fuse 15A	Combiner box on roof or wall	One string missing, half output or none	PKR 900 each
DC isolator 1000V	Roof and beside inverter	Blank screen, no DC voltage at inverter	PKR 3,500 to 6,000
AC MCB 32A	House distribution board	Inverter runs then trips out	PKR 1,200 to 2,500
Type II SPD cartridge	Combiner or AC board	Green window turned red after a storm	PKR 4,000 to 7,500
Cooling fan module	Inverter base or side	Derating and heat alarms in afternoon	PKR 4,500 to 8,000
Board level repair	Service centre	Hard fault, no recovery after reset	PKR 18,000 to 45,000

Check three: is it actually the grid?

Grid-tied and hybrid inverters are required by their own firmware to disconnect when the LESCO supply steps outside a voltage or frequency window. That is not a fault. That is the machine obeying the standard it was certified against.

Two Lahore-specific patterns show up constantly:

1. Afternoon over-voltage. On feeders where many houses have gone solar on the same transformer, line voltage in the early afternoon can climb past 255 or 260V. Anything above the inverter's upper limit forces a disconnect. Wapda Town and parts of Bahria have visible clusters of this. The system then reconnects at 4 or 5 pm and the homeowner assumes the inverter is intermittent.
2. Evening under-voltage and brownouts. In older Mughalpura and Walton feeders the voltage sags in the evening peak. A grid-tied inverter simply stops. A hybrid with a battery rides through it if the battery is healthy.

The fix is rarely the inverter. Sometimes the installer can raise the grid voltage window inside the firmware if the brand allows it. Sometimes the AC cable run from inverter to meter is undersized, which adds its own voltage rise, and rewiring in 6mm or 10mm copper solves it. Sometimes it is a genuine LESCO transformer problem and the complaint goes to the SDO office. That last one is slow and nobody enjoys it, but there is no shortcut around a bad feeder.

Reading the app before calling anyone

If your build has a WiFi dongle, the app history settles this argument in two minutes. Look at the grid voltage curve for the past week. If the dropouts line up with a voltage spike each afternoon, it is the grid. If the dropouts happen at random times with normal voltage, look inward at the DC side or the unit.

Check four: the install, not the inverter

This is where honesty matters. A meaningful share of "inverter failures" in Lahore are workmanship failures from the original install, and they show up in year two or three.

• Loose DC lugs. Aluminium-to-copper joints and under-torqued MC4 crimps heat up, oxidise, and eventually open. The burnt smell around a combiner box is unmistakable.
• MC4 connectors from two different brands mated together. They physically click but the contact pressure is wrong. After a couple of Lahore summers they arc.
• Undersized DC cable on long roof runs. Common on 10kW builds where the array sits at the far end of a large roof. Voltage drop pushes the string below the MPPT start voltage on cloudy mornings.
• No earthing, or earthing tied into the house neutral. Half the inverter faults labelled ground fault in Lahore are simply a missing earth rod.
• Water ingress into the combiner box after monsoon. A box mounted with the glands facing up will fill. Guaranteed.

If the same fault keeps returning after resets, the cause is almost always in this list. A proper solar repair visit starts with a thermal check of every joint before anyone talks about replacing hardware. Costs for common jobs are set out in the Lahore solar repair cost guide.

Check five: when it really is the inverter

After the isolators, fuses, grid window, and joints have been cleared, a genuine unit failure looks like one of these:

• A hard fault code that returns immediately after every reset, with the DC side confirmed healthy at the terminals.
• Burn marks, a bulged case, or a sharp electrical smell from the vents.
• Correct DC voltage present at the input terminals but zero AC at the output while the grid is within limits.
• Display corrupted, buttons unresponsive, unit stuck in a boot loop.

At that point the decision is repair or replace. Brands with a real Lahore presence get repaired: Inverex and SolarMax both have service capacity in the city, and board-level work runs PKR 18,000 to 45,000. Solis and Growatt usually go through the importer. A Huawei unit is generally swapped rather than repaired.

New hybrid pricing today: 3kW at PKR 95,000, 5kW at PKR 165,000, 6kW at PKR 158,000, and 10kW at PKR 295,000. If a repair quote crosses about 40 percent of a new unit, and the unit is past five years old, replacing is the better money. Worth saying plainly though: a replacement inverter on an install with the original bad wiring will fail again. Fix the cause first.

What to do while you wait for the technician

Turn the system off in the correct order and leave it off if there is any smell, heat, or visible damage. AC breaker first, then the DC isolator beside the inverter, then the roof isolator. Powering back up runs in reverse. Doing it the wrong way around pulls a DC arc across the isolator contacts, which is exactly how those contacts get destroyed in the first place.

If you have a hybrid with storage and the house has gone dark, check whether the battery is simply flat and locked out rather than the inverter being at fault. That is a separate diagnosis covered in solar battery not charging and no backup at night.

One caveat homeowners deserve to hear: a technician cannot always find an intermittent fault in a single visit. A unit that trips once every three days with no code stored will need a logger left on site for a week. Anyone who promises a same-hour answer on an intermittent fault is guessing.

Preventing the next callout

Lahore is hard on this equipment. Smog season leaves an oily film on panels, monsoon drives water into anything not sealed properly, and May through July regularly puts wall-mounted inverters into thermal derating. Three habits cut callouts sharply.

Get the DC joints checked once a year, ideally before monsoon in late June. Keep the array clean so strings stay balanced, which the panel cleaning service handles on a schedule. And keep the inverter out of the sun and out of an unventilated store room, which is covered in detail in inverter overheating in Lahore summer.

If the system is on LESCO net metering, one more thing matters. A dead inverter for three weeks means three weeks of import at full retail slab rates, PKR 48 to 65 per unit. On a 10 marla house in Johar Town that is real money, often more than the repair itself. Fixing it in week one is cheaper than fixing it in month two. Planning a new build instead? Start with the sizing calculator or read 2026 installation costs.