How an oil-fired cylinder and its controls work together

Understanding an oil-fired cylinder and its controls before you spend money

A cylinder thermostat strapped to the tank tells the system when the water has reached temperature, closing a motorised valve to stop the boiler firing for hot water once satisfied. Programmers or separate timers control when heating and hot water are called for independently, which matters on an oil system since running the boiler purely for hot water outside of scheduled times uses fuel unnecessarily. Unvented cylinders add pressure and temperature relief valves and an expansion vessel as safety features that a vented, tank-fed cylinder does not need.

Detail that affects your quote for an oil-fired cylinder and its controls

• A cylinder thermostat stops the boiler firing once water reaches temperature
• Motorised valves route the boiler's output to heating, hot water, or both
• Independent timers avoid the boiler running purely for hot water needlessly
• Unvented cylinders need pressure and temperature relief valves as safety devices
• Faulty motorised valve actuators are a common cause of no hot water despite a working boiler

Questions we get asked

Why does my hot water take a while to reheat after a bath?

Cylinder reheat time depends on coil size, boiler output and how far the water temperature dropped, and it is worth checking against the cylinder's stated recovery time if it seems unusually slow.

Can the boiler run just for hot water without the heating coming on?

Yes, provided the programmer and motorised valves are set up correctly to call for hot water independently of the heating circuit.

Does an unvented cylinder need annual checks?

Yes, its safety devices such as the pressure relief valve should be checked at the same time as the boiler service to confirm they still operate correctly.

Where we deal with this

• Beckington (BA11) · 5 mi
• Corston (BA2) · 7 mi
• East Harptree (BS40) · 7 mi
• Hilperton (BA14) · 10 mi