Before operating any gas appliance, what precaution should be taken regarding installation?

Ensuring that all installation procedures have been followed is crucial before operating any gas appliance. This step is vital because adherence to the manufacturer's guidelines helps to ensure the appliance is set up safely and correctly, minimizing the risk of gas leaks, malfunctions, or unsafe operation.

Manufacturer's manuals provide specific instructions on clearances, venting requirements, gas supply connections, and safety checks that are tailored to the appliance. Following these procedures ensures that the appliance operates efficiently and safely, which is critical for the protection of the user and the property.

The other options do not support safe operational practices. For instance, verifying that the manufacturer's manual is lost is not a precautionary measure; instead, having access to the manual is essential for accurate installation guidance. Ensuring all seals are loose contradicts safety principles since proper sealing is required to prevent gas leaks. Testing buttons for functionality is important but is secondary to confirming that the appliance has been installed correctly according to safety protocols.