There are two kinds of solar water-heating system. One is a closed-loop system, used for heating spaces; the other is a system to heat water for domestic use in showering, washing dishes and cooking. Both systems use pumps to circulate the heated water. If the pump breaks, the water stops moving and the system doesn't work. Pumps wear out over time and need replacing. The hotter the water they pump, the faster they wear out; they should be installed in the coolest part of the system. Some pumps contain removable cartridges, while others need to be completely replaced when they malfunction.
Sensor Wire Malfunction
A sensor wire keeps track of the temperature of the water in the system and signals the circulating pump when to turn on and off. If the contact between the sensor and the pump breaks, or if the two are separated through some other error, unpleasant consequences can follow. The pump could run continuously, burning out or preventing water from being properly heated. Or the pump could cease to come on, creating the hazard of leaving water standing in the rooftop panels and overheating. If the water gets too hot, it could cause pipes to rupture, possibly causing water damage inside the home.
Expansion Tank Problems
An expansion tank is an important component of a solar hot-water system. Because water density changes with temperature, it can't maintain a constant pressure within a closed loop system without an expansion tank that accepts water as it expands and then releases it, maintaining the same pressure, as it contracts. If a system is installed with an expansion tank that is too small, the excess pressure could lead to failure of various system components. Also, if an expansion tank is left too long without inspection or maintenance, it may age and corrode to the point where it will cease to function properly. Extreme rust or corrosion could lead to leakage, probably at the joints connecting the tank to the system.