SolarEdge optimiser communication failure — what P404 means and how to fix it
SolarEdge Go is showing a P404 fault code — optimiser pairing lost. The inverter has stopped communicating with one or more optimisers over the DC power line. This guide explains what's causing it, whether a reset will fix it, and when you need an engineer on site.
Tell us how many optimisers show P404, whether it appeared after a firmware update or gradually, and any SetApp screenshots. We confirm whether it's a wiring fault or failed units before any site visit.
Book P404 diagnostic → All SolarEdge problemsSingle P404 vs full-string P404 have completely different causes. We identify which before recommending action.
P404 ("optimiser pairing lost") is the active fault code reported by SolarEdge Go when the inverter has lost its communication pairing with an optimiser over the DC power line. N/A is the label the monitoring portal displays when no data is arriving from that panel. In most cases, a P404 fault produces an N/A status — but the code gives more diagnostic detail about timing and cause. If you're seeing N/A in the monitoring portal but haven't checked SolarEdge Go, do that first — the Go app may show a P404 code that significantly narrows the investigation.
Not sure which page you need? See the optimiser showing N/A guide for the monitoring portal view and pattern-based diagnosis.
How to diagnose SolarEdge P404 communication failure
The key question is whether P404 is a pairing/firmware issue (often resolvable with a reset) or a physical fault (needs an engineer). These steps determine which it is.
Open SolarEdge Go and confirm P404 — note the count and pattern
Connect to your inverter via SolarEdge Go on Bluetooth. Stand within 3–4 metres of the inverter. Navigate to Alerts or the Device Status section. Confirm you're seeing P404 — "Optimiser pairing lost" — and not a different code. Take note of:
Log into monitoring.solaredge.com and check the layout view. Optimisers with P404 will typically show as N/A (greyed out). Note whether they are in a consecutive run or scattered — this distinction is covered in step 3.
Check whether a firmware update ran in the past 48–72 hours
In the monitoring portal, go to the system's inverter details page and check the event log for any firmware update activity. SolarEdge pushes OTA updates to inverters automatically — sometimes without any notification to the system owner. A firmware update is one of the most common triggers for P404 in otherwise healthy systems, because the update process can break or reset the inverter's pairing table with its optimisers.
This is a pairing re-establishment issue. Try the soft reset in Step 3 — most post-firmware P404 faults clear within one or two resets. If they don't, a manual re-pairing via SolarEdge Go by an engineer is the likely fix.
More likely a physical cause — wiring break, failing connector, or failed optimiser. Proceed through the steps, but expect an engineer visit is likely needed.
Read the pattern — consecutive or scattered?
The pattern of P404 faults in the monitoring portal layout is one of the most important diagnostic signals. It tells you whether to expect a single root cause or multiple independent failures:
Usually a failed optimiser unit or a single faulty connector at that unit. The rest of the string is unaffected. Check warranty — 25-year cover applies.
PLC chain broken at the first affected unit. Single root cause — look for a connector or cable fault at or just before that panel. Not multiple failures.
Inverter-side communication issue. Often firmware or a DC bus fault. Check whether the inverter display is lit and whether any string data shows in the portal.
Scattered P404 (non-consecutive, across different strings) is rarer and may indicate multiple ageing optimisers approaching end of life, particularly in older pre-2016 installations.
Attempt a soft reset — AC isolator off for 90 seconds, then on
Before calling an engineer, try one soft reset. The 90-second wait (longer than a standard reset) allows the optimisers' PLC pairing state to fully clear before the inverter restarts and attempts re-pairing. At the consumer unit, switch the solar PV circuit breaker OFF. Wait 90 seconds. Switch back ON. Allow 15–20 minutes for the system to restart and the monitoring portal to refresh.
The fault was a pairing glitch or post-firmware disruption. Monitor over the next 3–5 days. If P404 does not return, no further action needed. If it returns intermittently, book an engineer — intermittent P404 suggests a marginal connector or cable developing a fault.
Physical fault confirmed. There is a break in the DC power line communication chain — a wiring fault, connector fault, or failed optimiser. An engineer visit is required. Do not continue resetting.
Only attempt a reset if you have not seen P700 or P701 (arc fault) codes. Arc fault events must not be reset — see the arc fault guide if those codes are present.
Contact a qualified engineer for re-pairing or physical repair
If the P404 persists after a reset or keeps coming back, book an engineer. Have ready:
The engineer will connect via SolarEdge Go and attempt a re-pairing sequence first. If that does not restore communication, they will proceed to physical DC string testing and inspection to find the underlying cause.
What causes SolarEdge P404 communication failure?
P404 has three distinct cause categories — each with a different resolution path. Knowing which you're dealing with determines whether this is a same-day reset fix or a site visit.
Firmware update disruption — most common cause of sudden P404 on a healthy system
SolarEdge automatically pushes OTA firmware updates to inverters, typically overnight. The update process can disrupt the inverter's pairing table — the internal record of which optimisers are registered to the system and on which string positions. When the inverter restarts after the update, some or all optimisers may fail to re-pair automatically, producing P404.
This is not a hardware fault — the optimisers themselves are undamaged. The inverter simply needs to re-establish the PLC pairing with each unit. A soft reset (90-second power cycle) is usually sufficient. In cases where the pairing table has been significantly disrupted, an engineer may need to connect via SolarEdge Go and initiate a fresh pairing scan — a process that takes 10–20 minutes on site but does not require any physical work on the roof.
DC power line communication break — wiring fault or failed connector
SolarEdge optimisers use power line communication (PLC) — they superimpose a high-frequency data signal onto the DC power cable to relay information back to the inverter. PLC is reliable when the DC circuit is intact and the cable quality is good. But any fault that increases resistance or breaks continuity in the DC line also breaks the PLC signal:
Physical PLC breaks do not clear on reset — the fault is in the DC wiring and persists until repaired. The pattern of P404 (consecutive run starting at a specific panel) points the engineer to the right section of string.
Failed optimiser unit — hardware failure stopping both power and communication
A power optimiser that has failed completely stops functioning as both a power converter and a PLC relay. Depending on how it fails, it may either break the PLC chain (causing all downstream units to also show P404) or simply drop off the chain without affecting others. Either way, the monitoring portal shows the failed unit as N/A and SolarEdge Go reports P404 for it.
Hardware failure of an individual optimiser is more common in older installations (pre-2016) and in early S250/S270 series units. SolarEdge's 25-year warranty covers the replacement unit — but confirming the fault requires an engineer with SolarEdge Go to test the unit in-situ and document the failure before SolarEdge will process the warranty claim.
What the engineer will do on site for P404
The engineer's approach for P404 differs depending on whether the cause is likely a pairing/firmware issue or a physical fault. SolarEdge Go allows a significant portion of the diagnosis to happen before any roof access.
The engineer connects to the inverter via SolarEdge Go and reviews the full fault log. They check when the P404 first appeared, which optimisers are affected, and what firmware version the inverter is running. SolarEdge Go's commissioning mode allows the engineer to initiate a fresh pairing scan — the inverter broadcasts a pairing request and all functional optimisers within range respond. This test immediately distinguishes a pairing issue (optimisers respond to the scan) from a physical fault (optimisers do not respond at all).
If the SolarEdge Go pairing scan finds the optimisers but they are not registered to the inverter's pairing table, the engineer will initiate a fresh pairing and commissioning sequence. Each optimiser is re-registered using its serial number. This process takes 15–30 minutes depending on the number of optimisers. Once complete, the system is restarted and the engineer confirms all previously P404 optimisers are now showing normal output data. No roof access is required for a pairing-only fix.
If the pairing scan shows optimisers are not responding at all — meaning the PLC signal is not reaching them — the engineer will perform DC string continuity and voltage measurements at the inverter input. A break in the string will show as an open circuit or reduced DC voltage. The position and magnitude of the voltage drop narrows the physical location of the fault to a specific section of cable or a connector on the roof.
With the fault location identified from step 3, the engineer accesses the roof and physically inspects the connectors and cable in that section. Faulty MC4 connectors are replaced. If the fault is in the cable, the damaged section is repaired or replaced. If an individual optimiser has failed, it is replaced — using the SolarEdge warranty claim process if within the 25-year warranty period. After any repair, the engineer restarts the system and confirms the repaired section is communicating and producing normally in SolarEdge Go before leaving the site.
How SolarEdge power line communication works — and why P404 happens
SolarEdge uses a communication method called power line communication (PLC) to send data between the optimisers and the inverter. Rather than separate signal wiring, the optimisers superimpose a high-frequency data signal directly onto the DC power cable. The inverter reads these signals from all optimisers simultaneously, giving it panel-level production data, fault codes, and control capability over each unit.
For PLC to work, there needs to be a complete, low-impedance DC circuit from the inverter through each optimiser and back. The optimisers communicate in a chain — each unit acting as a relay for those before it in the string. This architecture is why a break at a single point causes all subsequent optimisers to go silent: the relay chain is interrupted, and the data cannot reach the inverter past the break point.
The PLC pairing is established when the system is first commissioned. The inverter scans the string, discovers each optimiser by its unique serial number, and registers it in its pairing table. This table persists in the inverter's memory — but a firmware update that overwrites or corrupts the pairing table can require this process to be repeated. This is why a re-pairing sequence in SolarEdge Go can restore communication without any physical work on the roof when the cause is firmware-related.
P404 is the fault code that results when an optimiser that was previously in the pairing table stops communicating — regardless of whether the cause is a firmware disruption, a hardware failure, or a physical wiring fault. The code doesn't distinguish between these causes, which is why the diagnostic steps in this guide (pattern analysis, firmware check, soft reset, pairing test) are needed to identify which applies.
SolarEdge P404 communication failure — frequently asked questions
P404 is SolarEdge's "optimiser pairing lost" fault code. It appears in SolarEdge Go when the inverter has lost its PLC (power line communication) connection with one or more optimisers. The affected optimisers will typically also show as N/A in the monitoring portal. P404 can be caused by a firmware update disrupting the pairing table, a physical fault in the DC string, or a failed optimiser unit. It is not a safety event — unlike P700/P701 (arc fault), P404 does not require immediate isolation.
Yes — post-firmware P404 is a well-documented occurrence with SolarEdge systems. SolarEdge pushes OTA updates automatically, often overnight. The update can disrupt the inverter's optimiser pairing table, resulting in P404 for some or all optimisers the next morning. Try a 90-second soft reset (AC isolator off, wait 90 seconds, back on) and allow 15 minutes for the portal to update. This resolves most post-firmware P404 faults. If P404 persists after two reset attempts, an engineer will need to connect via SolarEdge Go to run a fresh pairing scan.
They describe the same underlying condition from two different views. N/A is the label the monitoring portal shows when an optimiser stops reporting data — it means the portal has no current data for that unit. P404 is the active fault code that SolarEdge Go (Bluetooth) shows when the inverter has explicitly lost its pairing with the optimiser. In most cases both appear together, but SolarEdge Go gives more detail — timing, specific unit identification, and access to the pairing reset function. If you see N/A in the portal, check SolarEdge Go for the corresponding P404 code to get the full picture.
Sometimes. P404 caused by a firmware update or a temporary communication glitch often clears on a 90-second soft reset without any engineer involvement. P404 that persists after two reset attempts, or that keeps recurring after clearing, indicates a physical fault — a connector, cable, or failed optimiser — which cannot be resolved remotely. The pattern of affected optimisers (post-firmware vs no obvious trigger, clearing vs persistent) helps determine which category applies before a visit is booked.
If the cause is a pairing or firmware issue, the engineer can often resolve it in 30–45 minutes on site without roof access — just a SolarEdge Go session and a re-pairing sequence. If a physical fault is confirmed (connector, cable, or failed optimiser), the visit extends to a half day. Optimiser replacement under warranty adds some administrative time, but the physical swap is quick. Most P404 investigations are resolved in a single visit, and the engineer can usually tell the homeowner before going on the roof which scenario they're dealing with.
Other SolarEdge problems
Understanding the N/A status in the monitoring portal and how to read the pattern for diagnosis.
P700/P701 — a safety event requiring isolation, not a reset. Different fault type to P404.
System running but generating zero output — DC, AC, and firmware causes covered.
Steady or flashing red LED — what each pattern means and what to do.
SolarEdge P404 — let's identify the cause and get communication restored.
We diagnose P404 faults using SolarEdge Go — starting with a pairing test and re-pairing attempt before any roof access. If the fault is physical, we trace the string and carry out the repair. Optimiser warranty claims managed with SolarEdge.
This is a brand-specific version of our general system not producing guide, which covers all brands.