In This Guide
What does the central heating pump do?
The circulation pump is what pushes hot water from the boiler out through your radiators and back again. If it stops working, the boiler can still fire and heat water, but that heat never reaches the radiators, so you get a hot boiler and cold radiators. That combination is the clearest sign the pump, rather than the boiler, is the problem.
Other signs of a failing pump are no hum or vibration when you rest a hand on it, a pump that is hot to the touch but not moving water, gurgling or buzzing noises, or a small leak from the pump body.
Why is my central heating pump not working?
Most pump faults come down to one of a handful of causes, and the sign usually points to which:
Cause | Sign | Typical fix |
Seized pump (sludge or wear) | No hum or vibration, radiators cold | Free or replace the pump; power flush if sludge is the cause |
Airlock | Pump runs but circulation is poor, gurgling | Bleed the pump and radiators |
Electrical fault | Pump completely dead, no power | Check the fuse and wiring, then engineer repair |
Stuck impeller | Humming but no circulation | Free the impeller or replace the pump |
Worn bearings or age | Noisy or overheating pump | Pump replacement |
Sludge is behind a large share of seized pumps, so if the system is old and has never been flushed, a power flush often solves the immediate fault and prevents the next one. The same restricted circulation can also show up as boiler lockouts, which is why a pump problem and an Ideal L1 low water flow fault frequently share a root cause.
What you can check yourself
There are a few safe checks before you call anyone. Make sure the pump has power and its fused spur or switch is on. Bleed the radiators to clear trapped air, and check the system pressure is between 1 and 1.5 bar when cold. If your radiators are warm at the top but cold at the bottom, or some are cold while others are hot, that points to air or sludge rather than a dead pump, and our guide to radiators not heating up fully covers those checks in detail.
What you should not do is start dismantling the pump or its wiring. Pump replacement and any electrical work is an engineer’s job, and on a combi boiler the pump sits inside the sealed boiler casing, which must only be opened by a Gas Safe registered engineer.
When to call an engineer
If the pump is silent with no vibration, if it hums but moves no water, or if it is leaking, it needs testing and almost always replacing. On a combi, because the pump is internal, that is Gas Safe work. Repeatedly resetting the boiler will not revive a failed pump, and running the system with a seized pump can stress the boiler further.
How 0800 Homefix fixes pump faults
0800 Homefix are Gas Safe registered engineers covering London and the South East. An engineer will confirm whether the pump has genuinely failed or whether sludge, air, or an electrical fault is the real cause, then repair or replace it and check the whole system circulates properly before leaving. You can see the full service on our boiler repair page, and regular boiler servicing is the best way to catch pump wear and sludge before they leave you without heat.
0800 Homefix charges as the first hour of labour, paid in advance, with any parts or further work quoted and agreed with you before it begins. For current rates, see our rates page. Our labour is guaranteed for 12 months, and any parts we fit are covered by the manufacturer’s 12-month guarantee.
Frequently Asked Questions
How do I know if my central heating pump has failed?
The clearest sign is a hot boiler with cold radiators. A failed pump also has no hum or vibration, may be hot but not moving water, and can make gurgling or buzzing noises.
Can I fix a central heating pump myself?
You can check the power, bleed the radiators, and confirm the pressure. Freeing, rewiring, or replacing the pump is an engineer’s job, and on a combi boiler the pump is inside the sealed casing and must only be worked on by a Gas Safe engineer.
Why is my boiler working but the radiators are cold?
That usually means the pump is not circulating hot water around the system. It may be seized, airlocked, blocked by sludge, or have an electrical fault.
How much does it cost to replace a central heating pump?
It depends on the pump and the boiler. 0800 Homefix confirms the fault first and provides a fixed price before any work begins, so you are not paying to replace a pump on a guess. See the rates page for current pricing.
Can sludge stop a central heating pump?
Yes. Sludge is one of the most common reasons a pump seizes. A power flush clears the debris and restores circulation, and helps prevent the pump failing again.
Helpful resources
- Gas Safe Register: check an engineer is registered before any work on a combi boiler.
- Energy Saving Trust: independent guidance on running an efficient heating system.
Spotted Any of These Warning Signs?
Hot boiler but cold radiators? 0800 Homefix has Gas Safe registered engineers across London and the South East who can test the pump, find the real cause, and get your heating circulating again, seven days a week, 365 days a year.
Editorial note: This article is intended as a general homeowner guide. All plumbing work on supply pipes should be carried out by a qualified, WaterSafe-registered plumber. If you suspect a gas leak, leave the property immediately and call the National Gas Emergency Service on 0800 111 999.
