Unvented
hot water.

An unvented cylinder stores hot water under mains pressure, and its safety devices exist to control that pressure and temperature. Scheduled servicing verifies that those devices operate, that expansion is being accommodated correctly, and that the cylinder and its controls are performing as intended.

• Expansion vessel charge and condition
• Pressure reducing and control valves
• Temperature and pressure relief valve operation
• Expansion relief valve operation
• Discharge arrangement condition
• Thermostat and control operation
• Immersion heating where fitted
• Recorded service outcome

Most cylinder complaints resolve to expansion, pressure or control. Loss of expansion capacity, an incorrectly set or failed pressure control, or a control fault will each present differently at the outlet, and each is confirmed by measurement rather than by symptom.

Work on unvented hot water systems is regulated. Work of that type is carried out only where the attending engineer holds the appropriate current competency for it. Where a task falls outside that scope, it is identified and reported rather than undertaken.

Where hot water performance is reported, the cylinder is assessed with the systems around it — the incoming supply, the heat source serving it, the distribution and the controls — so that the fault is identified in the system rather than at one component.