Maintaining and fixing solar water heating systems

For solar energy systems to function effectively, regular maintenance and inspections are necessary. Additionally, parts might need to be repaired or replaced from time to time. Additionally, you should take precautions to avoid freezing, corrosion, and scaling.

Some of the inspections and maintenance jobs you might be able to undertake on your own, while others would need a trained specialist. For safety concerns, anything that necessitates climbing ladders, walking on rooftops, soldering or other hot work, or pruning back tree limbs, should be done by a professional service. Before starting any work, request a written cost estimate. It might be more economical to replace, turn off, or remove the solar system than to have it repaired for systems with significant damage.

Maintaining and fixing solar water heating systems

List of Regular Inspections

Here are some recommendations for solar system component checks. To manage preventative maintenance intervals and better monitor elusive problems, read your owner’s manual for a suggested maintenance schedule and keep account of previous maintenance operations.

  • Shading for collector. On a yearly basis, visually inspect the collectors for shading during midday (midmorning, midday), noon, and midafternoon. Shading has a significant impact on how well solar collectors work. Shade that wasn’t there when the collectors were placed may now exist due to new nearby construction or the growth of nearby vegetation.
  • Collecting dirt. Collectors that are dirty or dusty will operate badly. If rain is insufficient to sufficiently rinse them off, periodic cleaning may be required in locations with specialized sources of soiling like birds or dust from plows.
  • Sealing and glazing for collector. Examine the collector glazing for cracks and make sure the seals are in good shape. If the plastic glazing has gotten too old, it might need to be replaced.
  • Wiring connections, ductwork, and plumbing. Check the pipe connections for fluid leaks. Examine the duct connections and seals. It is advisable to use mastic to seal ducts. Every wiring connection needs to be secure.
  • Insulation for cables, ducts, and pipes. Verify that every valve is set up to function properly. Look for duct, pipe, and wiring insulation that has been damaged or deteriorated. Wrap the pipe insulation in metal or plastic for protection, and replace as necessary. Guard wiring in conduits.
  • Roof piercings. As necessary, maintain the flashing and sealant around roof penetrations. Keep an eye out for any indications of water leaks on the roof’s underside (if visible).
  • Support systems. Verify the tightness of each nut and bolt holding the collectors to any supporting structures. Keep an eye out for corrosion on steel parts, and if required, clean and paint.
  • Valve for pressure relief (on liquid solar heating collectors).To check sure the valve is not jammed open or closed, move the lever.
  • Dampers (in solar air heating systems) (in solar air heating systems). If at all feasible, confirm that the dampers are in the right place and open and close properly.
  • Blowers or pumps. Check to see if the fans or blowers are working. When the light is shining on the collectors after mid-morning, listen to see if they start up. If a pump or blower isn’t making any noise, either the controller or the pump or blower is broken. The starting capacitor is frequently the culprit and may be changed without having to change the pump or motor.
  • Controls. A temperature sensor on the solar collector outlet, another at the bottom of the solar storage tank, and a circuit (delta-T controller) that starts the pump when the collector is hotter than the tank and shuts it off if it is not make up the solar water heating controls. The collection sensor may be shorted out or the tank sensor may be open circuited if the pump is running at night. The resistance of these sensors should be compared to a reference value in order to identify which one has failed if the pump is not operating during the day. Temperature sensors frequently fall off the surface they are supposed to be measuring, so make sure they are secured with a nut or stainless steel clamp.
  • Fluids for heat transfer. Propylene glycol antifreeze solutions need to be changed out periodically in liquid (hydronic) solar heating collectors. With the use of portable devices, it is possible to measure the fluid’s pH (acidity) and freeze point, and replenish it if necessary. It’s preferable to leave it to a trained professional. If hard water (water with a high mineral content) is circulated directly in the collectors, mineral buildup in the pipework may need to be eliminated by adding a de-scaling or mildly acidic solution to the water every few years.
  • Storage devices. Verify storage tanks, etc., for any rust, cracks, or other corrosion-related symptoms. Steel storage tanks have a “sacrificial anode” that should be replaced at a frequency advised by the supplier because it corrodes before the tank does. Periodically flushing storage tanks to get rid of sediment is a good idea.
 solar water heating systems

Preventing Corrosion and Scaling

Scaling (in liquid or hydronic-based systems) and corrosion are two main problems influencing the operation of properly situated and installed solar water heating systems (in hydronic and air systems).


High mineral content drinking water, also known as “hard water,” can cause mineral (calcium) deposits to scale or build up on heat transfer surfaces. In several ways, scale accumulation lowers system performance. If the heat-transfer fluid in your system is water, the collector, distribution pipework, and heat exchanger may scale with time. Scaling may develop on the surface of the heat exchanger that transmits heat from the solar collector to the household water in systems that employ different forms of heat-transfer fluids, such as propylene glycol. Failures of the potable water loop’s valve and pump may also be brought on by scaling.

Scaling can be prevented by utilizing water softeners or by running a moderate acidic solution (like vinegar) through the residential hot water loop every three to five years, or more frequently as needed depending on the water’s conditions. Surfaces of the heat exchanger might need to be thoroughly cleaned. An alternative to a heat exchanger inside a storage tank is a “wrap-around” external heat exchanger.


Corrosion affects the majority of well-designed solar systems seldom. When they interact, it typically results in galvanic corrosion, an electrolytic process brought on by the contact of two dissimilar metals. One of the metals corrodes because the other is attracted to it by electrons from the other metal, which has a stronger positive electrical charge. Therefore, a “bi-metallic” type of connector that uses a plastic sleeve to separate the dissimilar metals should be used to connect the copper pipe to the steel tank. In some solar energy systems, the heat-transfer fluid can also act as a bridge for this electron exchange.

Any iron or steel component in an open loop hydronic solar system will rust if oxygen enters the system. The piping loop for such systems ought to be made of copper, bronze, brass, stainless steel, plastic, rubber, and have storage tanks with plastic or glass linings.

Protective Freeze

In areas with temperatures below 42°F (6°C), solar water heating systems that use liquids as heat-transfer fluids require protection from freezing.

Do not rely on the insulation of a collector or the pipes (collector loop) to prevent freezing. The insulation’s primary goals are to decrease heat loss and improve efficiency. You essentially have two choices for preventing damage from freezing conditions to the collector and piping:

  • As the heat-transfer fluid, use an antifreeze solution.
  • When there is a danger that the temperature will drop below the freezing point of the liquid, drain the collector(s) and pipes (collector loop), either manually or mechanically.


As long as the right antifreeze concentration is maintained, solar water heating systems that use an antifreeze solution as a heat-transfer fluid (always propylene glycol, never ethylene glycol due to toxicity) have effective freeze protection. Antifreeze fluids should typically be replaced every 3-5 years because they deteriorate over time. It is not practicable for the typical homeowner to verify the antifreeze solution’s state because these systems are pressured. If you have a system of this nature, have a solar heating expert inspect it sometimes.


When the home uses little hot water but the sun keeps heating the water, overheating happens. When a certain level is reached by the solar storage tank, the controller will shut off the pump (default 180F but often set lower to prevent scalding). The heat transfer fluid will prematurely degrade as the collector continues to heat up, which most systems can tolerate but may result in fluid discharge out of a pressure relief valve. You can prevent this fluid damage from overheating by draining the fluid back into a drainback tank. In some systems, a solenoid valve that opens to drain some water from the tank if it gets too hot.

Piping and Draining the Collector

The most prone to freezing damage are solar water heating systems that simply employ water as a heat-transfer fluid. A controller is generally used in “draindown” or “drainback” systems to automatically drain the collector loop. The controller receives instructions from sensors on the collector and storage tank as to when to stop the circulation pump, drain the collecting loop, and restart the pump.

The use of subpar sensors or improper location may prevent them from detecting freezing temperatures. If the controller fails to empty the system, costly freezing damage could result. Make sure the freeze sensor(s) have been fitted in accordance with the manufacturer’s instructions, and verify the controller’s functionality at least once a year.

There should be a way to stop a vacuum from developing inside the collector loop as the liquid drains out in order to guarantee that the collector loop drains fully. At the highest point in the collector loop, an air vent is typically built. Insulating air vents to prevent freezing is a recommended practice. As the drain cycle is running, make sure nothing is obstructing the airflow into the system.

To enable the water to drain entirely, collectors and pipelines need to slope properly. The minimum slope required for all collectors and pipework is 0.25 inches per foot (2.1 centimeters per meter).

The collector doubles as the storage tank in integral collector storage or “batch” systems. Large amounts of insulation should be placed around the collector’s unglazed areas, and the glazing should be covered at night or on overcast days to protect it from the cold. However, during prolonged periods of extremely cold weather, water in the collection may freeze. The supply and return pipes for the collector are similarly prone to freezing, especially if they pass through an area that is not heated or outside. Even if the pipes are well insulated, this is still a possibility. In order to prevent any potential freeze damage, it is best to drain the entire system before it becomes cold.

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