A central heating pump should only be replaced like for like after its dimensions, connections, electrical supply, control method and operating duty have all been checked. A similar-looking circulator is not necessarily an appropriate substitute.
For an external pump, the work normally involves electrical isolation and some loss of system water. If the pump is inside a gas boiler casing, use a Gas Safe registered engineer rather than opening the appliance yourself.
Start by identifying the pump and its position
Record the complete model designation and any part number from the existing pump before disturbing it. Photograph only externally visible details, such as the rating plate, pipe connections and control setting. Leave electrical covers and boiler casings to the appropriately competent tradesperson.
Establish whether the circulator is an external system pump or a component inside an appliance. Accessing a pump inside a gas boiler can involve opening the appliance casing, so refer this work to a Gas Safe registered engineer.
An external circulator may be fitted near the boiler, cylinder or other system components. Its location alone does not establish the replacement specification, so compare the existing unit with the current manufacturer's installation guide.
If the system has been losing pressure, investigate that problem rather than assuming a new pump will correct it. The BHL guide Boiler losing pressure: what you can check and when to call an engineer covers the subject indicated by its title.
What pump size means
Several separate details can be described as pump size. They include the distance between the pipe connection faces, the connection type and the hydraulic duty required by the heating circuit.
Do not treat one number in a model designation as a complete sizing specification. Read the full designation and check the dimensions and performance information in the current Grundfos or Wilo installation guide, as applicable.
Measure the installed length between the connection faces without relying on an estimate. Also check the available space around the body, the direction-of-flow arrow, the permitted mounting orientation and whether the electrical connection can be reached safely.
The system's required flow and resistance determine the hydraulic duty. A replacement selected only because it physically fits can still be unsuitable for the circuit, while an unnecessarily high setting can contribute to flow noise and poor control.
Where the original duty is uncertain, a heating engineer can assess the circuit and select the pump using the manufacturer's performance information. Readers should confirm all product details against the manufacturer's current data before ordering or installation.
Understand settings and controls
Older circulators may offer fixed speed choices, while electronic circulators can offer different control modes. The symbols and adjustment method vary by manufacturer and model, so retain the existing setting as a reference and use the correct installation guide.
A setting is not interchangeable with pump size. It changes how the selected pump operates, but it cannot make an incorrectly selected circulator appropriate for the system.
After replacement, the setting should be checked against the system design and observed operation. Warning signs such as persistent flow noise, poor circulation or uneven heating need diagnosis rather than repeated, arbitrary adjustment.
Some appliance-controlled pumps receive signals from the boiler or another controller. Do not assume that a standalone circulator with a similar body or connector will accept the same control arrangement.
Check the current ErP circulator requirements, including the current status and application of retained Regulation (EU) 641/2009, rather than relying on an old product label or an earlier guide.
Plan a safe like-for-like swap
Before work starts, confirm how the heating circuit will be isolated and how water will be contained. Pump isolation valves may reduce the amount that has to be drained, but aged valves can leak or fail to close fully.
Electrical connections should be handled by a competent person, with the supply safely isolated and proved dead before conductors or a plug connection are disturbed. Use a competent electrician for mains connections where the work is outside the heating engineer's electrical competence.
Approved Document P is the guidance for electrical safety in dwellings in England. Wales publishes its own editions, while Scotland and Northern Ireland have their own building standards. Use the guidance for the nation where the work takes place, and check whether BS 7671 applies.
Confirm the direction-of-flow arrow before fitting the replacement. Follow the manufacturer's instructions for orientation, sealing, venting, commissioning and any restrictions on running the pump without water.
Once circulation has been restored, inspect disturbed joints and valves for leakage and check the system pressure or feed arrangement as appropriate. Air introduced during the work can cause noise and poor circulation, so the system may need venting and its pressure checked again when cold.
For radiator venting guidance, see How to bleed a radiator: a step-by-step guide.
When the job is not truly like for like
A change in model family, connection arrangement, installed length, wiring, control signal or hydraulic duty makes further checking necessary. Adapter work or altered pipework can also turn a simple exchange into a wider system repair.
Poor circulation can result from a seized pump rotor, sludge, closed valves, air, control faults or a lack of electrical supply. Establish the cause before deciding whether the pump needs replacement.
If cable insulation is damaged, terminals show signs of overheating or water has reached electrical parts, stop and arrange competent inspection. Repeated pump failure also calls for investigation of the system and installation conditions.
Do not open a gas appliance casing to reach an internal pump. Use a Gas Safe registered engineer for that work and provide the appliance details as well as the pump information.
Frequently asked questions
Can any circulation pump replace an old one?
No. Compare the complete model information, installed dimensions, connections, electrical supply, control method, hydraulic duty, flow direction and mounting instructions before selecting a replacement.
What does the number on a pump mean?
Its meaning depends on the maker and model range. Do not infer a connection size, installation length or performance figure from part of a designation without checking the current manufacturer documentation.
Should the new pump use the old setting?
The old setting is useful evidence, but it is not automatically correct for a different pump or control mode. Commission the replacement in accordance with its instructions and the system's design requirements.
Can a homeowner replace a boiler pump?
A pump inside a gas boiler should be handled by a Gas Safe registered engineer because access can require opening the appliance casing. External pumps still involve water and electricity, so use suitably competent tradespeople where the work is beyond your skills.
Why is the heating noisy after a pump change?
Air, an unsuitable control setting, excessive circulation, restricted flow or another system fault can cause noise. Check commissioning, venting and system condition instead of assuming that increasing the setting will help.
Parts and products at BHL
BHL lists circulation pumps within the wider pumps range. The boiler spares collection is also available for appliance-specific repair work, which should be matched using the appliance and manufacturer information.
The Grundfos Pumps GFOS ALPHA2 GO 25-75 130 220-240V 9H circulator pump carries part number 93074268.
The Wilo Yonos PICO 25/1-6-130 (ROW) high-efficiency circulation pump carries part number 4215516.
