Audrey HayesBy Audrey Hayes

Updated November 2026

To reset a solar hot water system, you cut power to the controller, check for the fault that tripped it, clear the error, and restart the circulation pump and backup heater in the right order. Most resets take under thirty minutes. If the system trips again within a day, the reset was never the real fix, and the cause needs attention.

Before You Start: Safety and Preparation

Solar thermal loops can run hot, and the collector side can reach temperatures well above what the storage tank holds. Work on the controller and electrical side only after shutting off power at the breaker. If the system uses gas backup, turn the gas valve to the off position before touching the heater.

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  • Digital multimeter for checking voltage at the pump and sensors
  • Insulated screwdriver set
  • Flashlight and the controller manual or wiring diagram
  • Pressure gauge for the collector loop, if your system has one
  • Gloves and eye protection

Step-by-Step Reset Procedure

Step 1: Read the Controller Display

Most differential controllers show a fault code or a status message such as “sensor error,” “overheat,” or “pump fault.” Write the code down before doing anything else. The code tells you whether the problem is electrical, thermal, or hydraulic.

Step 2: Cut Power and Let the System Settle

Switch off the controller breaker and wait at least five minutes. This clears volatile controller memory and gives the pump time to stop. If the collectors were in stagnation during a hot, sunny spell, wait longer and let them cool before touching any fittings.

Step 3: Check the Fault Source

Before restoring power, look at the likely cause for your error code:

  • Low loop pressure: Check the gauge. Many closed-loop systems run around 15 to 30 psi cold, depending on the manufacturer’s spec. Top up with the specified heat-transfer fluid only.
  • Sensor error: Check sensor wiring at both ends for loose or corroded connections. A reading of open circuit usually means a broken wire.
  • Overheat shutdown: Confirm the tank temperature is below the controller’s high-limit setting before restarting.
  • Pump not running: Measure voltage at the pump terminals while the controller calls for heat.

Step 4: Restore Power and Trigger a Test Cycle

Turn the breaker back on and watch the display. Most controllers run a self-test. Confirm the pump starts when the collector is at least several degrees warmer than the tank bottom, which is the usual on-threshold. If the pump runs and the collector outlet temperature starts to climb, the reset worked.

Step 5: Confirm Backup Heater Operation

If you have a gas or electric backup, check that it reengages when the tank drops below its setpoint. A backup that stays off after a reset can leave you with cold water.

Common Mistakes to Avoid

  • Resetting repeatedly without checking the code, which hides a recurring fault.
  • Opening the collector loop while the collectors are hot.
  • Adding water or the wrong antifreeze to a closed loop instead of the specified fluid.
  • Ignoring a sensor fault because the system seems to work anyway.
  • Skipping the manual, since reset sequences vary by controller brand.
  • A digital multimeter lets you confirm voltage and sensor resistance before and after the reset. View on Amazon
  • A pressure gauge for the collector loop shows whether the system has lost fluid. View on Amazon

FAQ

How often should a solar hot water system need a reset?

A well-installed system should rarely need a manual reset. Frequent trips point to a sensor, pressure, or wiring problem that should be diagnosed.

Will resetting the system erase my settings?

Most controllers keep their programmed setpoints through a power cycle, but check the manual first and note your settings before you begin.

When should I call a professional?

Call a licensed installer if you find a gas leak, a burned wire, a pressure loss you cannot trace, or a fault that returns within a day. Gas and high-voltage work should always be left to qualified people.

Conclusion

A reset clears a fault, but the error code tells you whether the fix is lasting. Check the code, verify pressure, sensors, and pump operation, then restart and confirm the backup heater responds. For more on setup and backup options, see Solar Hot Water System With Gas Backup: How to Set It Up Right.

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Audrey Hayes

About Audrey Hayes

Audrey Hayes is part of our editorial team and reviews and edits our solar water heaters guides, checking product details against manufacturer specifications and owner feedback.