Solar PV

Solar inverter overheating

Warning Do not attempt any electrical or gas work yourself. Always use a qualified, MCS-certified, or Gas Safe registered professional for repairs.

What you’re seeing (symptoms)

The inverter feels very hot to the touch. You may hear its internal cooling fan running at high speed for long periods. On very sunny days, your generation graph shows a “flat top” or a sudden dip in the middle of the day (this is called “thermal throttling”). The inverter may display a “High Temp” warning or error code.

What’s normal vs not normal

Normal:

  • The inverter feeling “warm” (around 40-50°C) during peak generation.
  • The cooling fan turning on and off throughout the day.
  • A slight reduction in efficiency as the unit gets warmer.

Not normal:

  • The unit being so hot that you cannot keep your hand on the casing for more than a second.
  • The unit shutting down completely and only restarting once it has cooled.
  • The smell of hot plastic or “electrical burning” near the inverter.
  • A loud “grinding” or “rattling” noise from the cooling fan.

Likely causes (ranked)

  1. Poor ventilation: The inverter is installed in a small, unventilated cupboard or a hot loft without enough clearance around the cooling fins.
  2. Direct sunlight: The inverter is mounted on an outside wall in direct sun, causing the casing to absorb extra heat.
  3. Dust buildup: The heat-sink fins on the back or top of the unit are clogged with dust, pet hair, or cobwebs.
  4. Fan failure: The internal cooling fan has failed or is blocked by an object.
  5. Under-sized inverter: The solar array is too large for the inverter, forcing it to work at its maximum limit for too long.

Quick checks you can do safely

  • Clear the area: Ensure there is at least 150mm-300mm of clear space on all sides of the inverter. Remove any coats, boxes, or clutter stored near it.
  • Check for dust: Use a soft brush or a can of compressed air to gently clear any dust from the metal cooling fins.
  • Check the fan: Can you hear or see the fan spinning? If not, the fan may be stuck.
  • Check the location: If it’s in a loft, open the loft hatch during a heatwave to see if the increased airflow helps the system stay online.

When to call an installer

  • If the unit frequently shuts down with a “Temperature Fault” even after you have cleared all obstructions.
  • If the cooling fan is making a loud mechanical noise or has stopped completely.
  • If you want to relocate the inverter to a cooler location (e.g. from the loft to a garage or utility room).

Questions to ask your installer

  • “Was the inverter installed with the manufacturer’s recommended clearances?”
  • “Can we add an external cooling fan or improve the loft ventilation?”
  • “Is the ‘DC-to-AC ratio’ of my system within the inverter’s safe operating temperature range?”

Related NetZeroNow tools & guides

FAQs

How hot is too hot? Most inverters are designed to operate up to 60°C. If the internal sensors reach this limit, the unit will automatically reduce its power output (derate) to protect its delicate electronics. Why are they often in lofts? Lofts are convenient for installers because they are close to the roof panels. However, in summer, a loft can reach 40-50°C, leaving the inverter with no “cool” air to use for its own cooling. Will it catch fire? Extremely unlikely. Modern inverters have multiple safety “thermal cut-outs” that will shut the unit down long before it reaches a dangerous temperature. Does it need a fan? Some inverters are “passively cooled” (no fan) and rely on large metal fins. These are quieter but even more sensitive to poor airflow. Can I put a desk fan next to it? Yes, as a temporary measure during a heatwave, a simple desk fan pointed at the inverter’s cooling fins can often stop it from throttling or shutting down.\n

Written by NetZeroNow | Last updated on 2026-03-02