Where is a manual shut-off valve usually located in a gas-fired heating system?

A manual shut-off valve is an essential safety feature in gas-fired heating systems, and it is typically located at various points to ensure safety and accessibility. The positioning of these valves is crucial for enabling easy shut-off of gas supply during maintenance or in the event of a leak.

Having a valve near the boiler allows for immediate access for the service technician to shut off the gas supply while performing repairs or maintenance, ensuring safety for both the technician and the surrounding environment.

Placing a shut-off valve at the main gas line is a standard practice as it provides a critical shut-off point that controls the flow of gas to the entire heating system. This is particularly important for emergency situations where an immediate shut-off is required to prevent hazards.

Additionally, having shut-off valves at each appliance enhances safety by providing localized control. If an issue arises with a specific appliance, such as a fireplace or furnace, the valve can be closed without affecting the gas supply to other appliances.

Thus, the inclusion of shut-off valves at the boiler, at the main gas line, and at each appliance exemplifies comprehensive safety measures within a gas-fired heating system, which is why the correct answer encompasses all of these locations.