To minimize thermal shock on hot water boilers, which of the following devices is NOT used?

To minimize thermal shock on hot water boilers, it is crucial to manage the flow of water and maintain stable temperatures. A boiler blowdown valve is primarily used to remove sediment and impurities from the boiler water. Its main function is related to maintaining water quality and operational efficiency rather than thermal management.

When it comes to managing temperatures and flow to prevent thermal shock—sudden temperature changes that can cause stress on the boiler structure—the other devices play significant roles.

Low limit control helps ensure that the water temperature does not drop too low, maintaining a constant temperature and reducing the risk of thermal shock.

A three-way valve allows for better control of the flow and temperature of the water being circulated. It can help blend hot water returning from the system with cooler water returning from the system to maintain a more consistent temperature throughout.

The run around pump is used for heat recovery and can promote the circulation of hot water, further aiding in temperature stabilization.

In contrast, the boiler blowdown valve does not serve a direct purpose in regulating or stabilizing boiler temperatures and therefore is not used to minimize thermal shock.