Growatt Error 04 — Insulation Fault: Causes, Safety, and Diagnosis
DC insulation resistance has fallen below the safe threshold (typically 1MΩ for UK G98). This is a genuine safety event requiring immediate isolation. Most common cause: MC4 connector water ingress on older installations. This guide covers every diagnostic step.
Your inverter has detected an insulation fault and shut down as a safety measure. Work through this diagnostic guide to identify the cause. Most cases can be narrowed down remotely, and we can advise on whether a site visit is required.
Book Remote Diagnostic — from £75 → Growatt hubSafety: Isolate the system at the consumer unit. Do not restart or override the fault.
6-step diagnostic process
Error 04 has four main root causes. Work through these steps in order to narrow down which is affecting your system.
Isolate immediately at consumer unit and DC string isolator
Error 04 is a safety fault. Switch off the main AC isolator at your consumer unit and the DC string isolator near the roof-mounted array. Do not touch any DC connections on the roof. Do not repeatedly restart the inverter in an attempt to clear the fault — this will not fix it and only risks exposure to live voltage.
Check ShineServer for when the fault first appeared and weather pattern
Log into ShineServer and navigate to Fault Logs. Note the exact date and time Error 04 first appeared. Check the weather on that date — if it appeared in the morning during wet or rainy weather, MC4 connector water ingress is almost certainly the cause. If it appeared after weeks of dry weather, a gradual cable or panel degradation is more likely.
Visually inspect MC4 connectors for water ingress
This step requires safe roof access. Inspect all MC4 connectors between the solar panels and the inverter. Look for: water droplets visible inside the connector housing, corrosion or whitish crystalline deposits, discoloured or corroded connector pins, or physical cracking of the connector body. Pre-2018 installations are most vulnerable — connectors degrade and lose weatherproofing over time. If you see water ingress, the connector must be replaced.
Inspect DC cable for UV damage or physical damage
Check the DC cable that runs from the roof array down to the inverter. Look for: cracks or splits in the cable insulation (often appear as fine white lines from UV exposure), physical damage from installation work or weather, crushed sections, or discolouration. Damaged cable insulation is the second most common Error 04 cause. Check the full cable run from roof to inverter.
Check individual panel junction boxes for cracks or failure
A failed or cracked junction box on a specific panel can cause localized insulation loss. If you can safely view the back of the panels (during a site visit), inspect the junction boxes for visible cracks, discolouration, or separation from the panel. A single faulty panel can often be isolated from the string by repositioning the string combiner input.
IR test verification before recommissioning
After the fault source is identified and repaired, a qualified engineer must perform an insulation resistance (IR) test on the DC string. Resistance must be ≥1MΩ as per UK G98 standards before the system can be safely restarted. Do not restart the inverter without documented IR test results.
Where you'll see Error 04
Inverter screen shows "Error 04" with a red LED indicator. The system stops generating and feeding to grid.
Log into ShineServer → Device → History. Filter by date and look for "Error 04" entries with timestamps.
Error history tab shows recent faults including Error 04 with timestamp.
Affected Growatt models
SPH-TL-BH series — hybrid inverters with battery
MIN-TL-X series — single and three-phase string inverters
MOD-TL3-X series — three-phase string inverters
ShineMaster range — older models with insulation monitoring
Typical repair costs
MC4 connector replacement
Replace the water-damaged connector pair. Quick fix if the fault is isolated to one connector.
DC cable replacement
Replace the damaged section of DC string cable. Cost depends on cable run length and roof access.
Panel junction box
Cracked or failed junction box requires panel replacement. May be covered under panel warranty.
What NOT to do
Repeated power cycles do not clear insulation faults. Each restart attempt increases stress on degraded components and may worsen the underlying issue.
DC circuits carry lethal voltage even when the inverter is off. Water ingress or damaged insulation create shock hazards. Only a qualified engineer should inspect DC wiring.
Insulation faults caused by moisture or damage are progressive — they worsen over time. A fault that appears occasionally will eventually become permanent.
About Growatt Error 04
Error 04 is the most common Growatt fault code in the UK, particularly on installations from 2015–2022. It affects SPH, MIN, MOD, and older ShineMaster models equally. The inverter detects DC insulation resistance falling below 1MΩ (G98 compliance threshold) and disconnects as a safety measure. This is not a Growatt hardware fault — it is almost always external to the inverter, indicating either connector degradation, cable damage, or a failed panel junction box.
ShineServer logs the exact time the fault appeared, allowing correlation with weather events. Morning appearance in wet weather almost always points to MC4 connector water ingress. Older installations on original equipment are most vulnerable due to connector age.
Error 04 questions answered
Yes. Error 04 indicates DC insulation resistance has fallen below the safe threshold. This is a genuine electrical safety event that creates risk of electric shock. The inverter shuts down as a protection mechanism. Do not attempt to override it or restart the system — isolate immediately and identify the fault source before operation resumes.
No. Repeatedly restarting the inverter will not fix Error 04 — it will only restart until the fault is detected again. This does not address the underlying insulation problem and risks electrical shock. The fault must be diagnosed and fixed before safe operation can resume.
Diagnosis varies depending on the cause. Water ingress in MC4 connectors can be identified quickly from ShineServer logs and weather timing. Cable faults require physical inspection. Panel junction box failures may require testing individual strings. Most cases can be narrowed down remotely in a single diagnostic session, but site visits are often needed for repairs.
Repair cost depends on the root cause. Water ingress at MC4 connectors: £30–50 parts plus labour. Damaged DC cable: £50–150 for replacement. Panel junction box failure: £200–400 for panel replacement. Our remote diagnosis from £75 identifies the fault location and provides a repair cost estimate.
Weather-dependent Error 04 is a classic sign of water ingress. Moisture in MC4 connectors or junction boxes increases when it's wet or humid, lowering insulation resistance until the inverter trips. This is a slow-developing fault that will eventually fail completely. Book a diagnostic soon — the fault location can often be identified from ShineServer history and weather correlation.
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Tell us what's happening. We'll review your ShineServer data and fault logs to diagnose the cause remotely — most cases are narrowed down in a single session.