Grundfos MAGNA3 circulating pump 1 x 230V PN10

Circulation pumps, or circulators, move water around a heating circuit or a hot water return loop so heat reaches every radiator and outlet. This category runs from compact domestic central heating pumps to large flanged single and twin-head pumps for commercial heating, and hot water circulators for secondary return systems.

Reading the model name

Many pump names follow a pattern: the first number is the nominal port size in millimetres and the second is the maximum head in decimetres, so a pump marked 40-80 has 40mm ports and up to about 8 metres of head. Letters add detail, such as F for flanged connections, D for a twin-head pump and N for a stainless steel housing. Domestic pumps also state the port-to-port length, often 130mm or 180mm, which must match the gap in the pipework.

Heating or hot water

• Heating circuits: standard pumps have cast iron housings and suit closed heating systems.
• Domestic hot water: the water in these systems is often aerated and would corrode cast iron, so return loops need a stainless steel or other housing approved for drinking water. Such pumps are marked as suitable for drinking water only.

Efficiency and replacement

Since August 2015, glandless standalone circulators have had to meet a minimum energy efficiency standard, and many now adjust their speed automatically to suit the system. When replacing a pump, match the port size, connection type, length, head and voltage, and the flange PN rating on larger pumps. Pump wiring should be done by a competent person to the current wiring regulations, and fittings on drinking water must be suitable under the Water Supply (Water Fittings) Regulations 1999.

For other pump types, see pumps; for hot water circulators, see hot water pumps.