What does the Unitrol in a residential water heater tank do?

The Unitrol is a component installed in residential water heater tanks that is primarily designed to enhance safety by shutting off the gas supply if the pilot light goes out. This function is crucial as it prevents the buildup of gas in the tank, which could otherwise create a hazardous situation if the gas were to accumulate without being ignited. Therefore, its role is a safety mechanism that directly impacts the operational safety of the water heater.

In contrast, the other options do not accurately reflect the function of the Unitrol. Increasing water temperature pertains to the thermostat or heating element, monitoring water levels is related to float switches or sensors, and adjusting water pressure can be managed by other plumbing components but is not a role of the Unitrol.