What should be checked before draining down a direct unvented cylinder?

Before draining down a direct unvented cylinder, it is essential to ensure that the immersion heater is turned off. This is critical for safety reasons, as draining the cylinder while the immersion heater is still operational can lead to damage to the heater itself or cause burns if the element is exposed without water cooling it. Moreover, any residual heat in the cylinder can lead to dangerous situations during maintenance or repairs.

In this scenario, having the immersion heater turned off not only prevents overheating but also ensures that there is no risk of scalding hot water being present, which is crucial for safe plumbing practice. Proper maintenance involves ensuring that all equipment is in a safe state before any work begins, and turning off the immersion heater is a key part of that process.