How to Test a Solar Thermal Installation

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Although the collectors are installed, the tank in place, the heat exchanger piped in and the plumbing done, there is no guarantee that your solar thermal system has no leaks. You need to test it before you fill the solar loop or allow water into the storage tank. You can check the system for leaks using air or liquids.

  • Testing with air has the benefit of no mess if there is a leak.
  • Testing with water cleans the system before you put solar fluid in.

Regardless of which method you use, it is important to fully check the system before charging. If possible, do the pressure test before you fit insulation around the joints – it will be a lot easier to find and fix problems without insulation in the way. This is especially true of external pipe runs, which should be tested before you bury them!

Air pressure testing

If you decide to go with an air test, you will need a way of pumping air into the system. You can do this with a bushing with a Schrader valve attached – take out a boiler drain and screw the fitting on in its place or, if the bushing has a hose thread, just attach it to the end of the drain connection.

Use a portable compressor to pump air into the system until it reaches at least 50lbs/in². You can monitor the pressure on the storage tank's valve. Once you reach that level, stop the compressor and watch the pressure gauge:

  • A serious leak will cause an immediate drop in pressure.
  • Smaller leaks will cause a slow deterioration.
  • Bear in mind that testing in daytime will cause pressure fluctuations due to heating.

As long as you have plenty of pressure in the system, any leaks will announce themselves by a whistling or hissing noise. Walk the pipe runs, listening at all joints for any sound of air escaping.

Water pressure testing

If you decide to go with a water test, there are two important considerations: damage from any leaks (especially in retrofits) and covering the collectors.

Any pressurized solar thermal system can produce steam, so it is vital that you cover the solar collectors before pumping any liquid into the pipes. This is not optional: you risk severe burns from very high-temperature liquids heated by uncovered collectors.

Do not put yourself in danger. Cover the collector array.

The pressure test is performed in the same way as charging the system for operation, but with simple water instead of a solar fluid mix. Please refer to the article covering how to charge a solar thermal system for a full equipment list and instructions.

Charge the system

Once you have pressure-tested the pipes and fixed any leaks, you can charge the system. Remember to remove the handles from the charging valves and keep them somewhere safe and convenient, and to install caps on all the drain valves.