This diagnostic guide covers every setting that can prevent charging. Work through the steps in order — most cases are resolved by the third step.
Book your free remote diagnosticSunsynk hubSafety: Isolate at the DC switch if you notice any error lights on the inverter or battery.
What a fantastic service. Had my fault diagnosed within minutes and actually managed to resolve the issue remotely within a few minutes more. This guy is like a “Solar Batman” helping consumers fix their problems using his extensive industry knowledge and expertise. Outstanding service. Thank you so much.
Massively massively recommended. We had a big battery array (49kW across three phases) put in four years ago. c £35k cost. It’s been a total nightmare for many reasons, not least 1. our installer being totally useless and unresponsive and 2. Givenergy, our battery supplier, going bust. Long story short it had never worked anywhere near properly despite countless hours on phones and emails; the best we’d achieved was one third of the batteries working. Rather than write it off, I asked a PM friend to try to source someone who could come on site and review and revive the system. He found Solar Tech Support and Ron. Ron assured us he was the man to get it going again. After so many years of pain, I was not convinced but, true to his word, five hours later it was up and running. Lovely chap, super knowledgeable with a support team to lean on who are also clearly super technical. I honestly didn’t think there was much chance of getting this array going ever again so was absolutely delighted when Ron and team pulled it off. Bravo!
Prompt and useful support regarding my Sunsynk system lack of performance. Ronald simplified the technical issues to make them understandable. Many thanks, looking forward to follow up.
Very very helpfuland so quick. Made sure that a non expert like myself understood what the problem was and how to resolve it.
Solar Tech Support answered my initial enquiry swiftly. They provided remote support to establish what the issue was, and through their experience and network, managed to get my clients system back online. Once the system was online, STS managed to diagnose the main issue to get the ac coupled inverter and battery back online, a battery repair was required. A site visit was organise and within a few days, the system was tested and back up and running. This has saved my client, and probably myself huge costs and inconvenience now the system is back online and working correctly. Would highly recommend.
I sent a message on their website regarding a problem I have on my Givenergy system. Although not supplied by Ronald, I thought it was worth an email. Within the hour on a Saturday, he phoned and we discussed the problem. He logged in remotely and gave excellent advice. I'm too far away for his on-site help but he did diagnose the problem and was happy also to chat through my thoughts about an upcoming solar/battery install I'm planning. Great bloke.... if only he was nearer!
Work through these steps in order. Most battery charging issues are resolved by Step 2.
Log into SolarMan, navigate to Device → Settings → System Work Mode. If the mode is set to Selling First, this is almost certainly your problem. Selling First mode maximises grid export and does not force charge from the grid or solar. Change to Time of Use (or the mode appropriate for your tariff) to enable charging windows.
In SolarMan, check the State of Charge (SoC) settings: target SoC (maximum charge level) and minimum SoC (discharge floor). If the battery is already at or above the target SoC, the inverter will not charge further — there's no work to do. For example, if minimum SoC is 90% and target is 90%, charging will never happen. Set minimum SoC to ~10-20% and target to 90-100% to allow the system to charge from near-empty to full.
In SolarMan, on the Device page, check the battery status. It should display a valid percentage (e.g., 45% SoC, 78% SoC). If the battery shows 0% or Unknown, the inverter has lost communication with the battery BMS. This prevents charging entirely. Check the CAN or RS485 communication cable between the inverter and battery — it may be loose, disconnected, or damaged.
In SolarMan, check the Time of Use charge window times. The window must exactly match your tariff's cheap-rate period. Common windows: Octopus Go 00:30–04:30 · Octopus Flux off-peak 02:00–05:00 · Economy 7 approximately 00:30–07:30. Also check that the inverter clock is set to current local time. During British Summer Time (BST), if the clock is still on GMT, the window will fire 1 hour late.
In SolarMan, find the grid charge settings (usually under Device → Settings → Grid Charge). Verify that grid charge is set to ON for the time windows where you want the battery to charge from the grid. If grid charge is disabled, the battery will only charge from solar generation, not from cheap-rate grid electricity.
If your Sunsynk has a CT clamp installed (for import/export monitoring), check that it's oriented correctly. In SolarMan, at night with no solar generation, the grid reading should show a positive value (import). If it shows negative (export) while you're clearly consuming from the grid, the CT clamp may be backwards. This can prevent charging from activating correctly.
Sunsynk hybrid inverters (3.6kW, 5kW, 8kW, 12kW models) are widely installed across the UK from 2020 onwards. They integrate directly with SolarMan monitoring (formerly PVMaster) and support native Octopus Agile, Intelligent, and Go tariff integration via Time of Use schedules. However, the SolarMan portal doesn't always clearly surface these settings, and many systems are delivered with factory defaults rather than customer-optimised configuration.
The result: nearly 30% of Sunsynk owners report battery not charging overnight despite having a charged battery and a cheap-rate tariff available. In almost all cases, it's a settings issue — System Mode set to Selling First, SoC headroom exhausted, or timezone mismatches — not a hardware fault.
Tell us what you're seeing. We'll review your SolarMan data and settings to identify the exact cause — most cases are resolved in a single remote session.
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