Heating 16 September 2026

Central Heating Pump Not Working? The Signs It Is Failing and What to Check First

If the boiler fires up and the hot water is fine but the radiators stay cold or only ever get lukewarm, the central heating pump is the first thing our engineers suspect. The pump pushes hot water round the radiators, and when it stops doing that the boiler heats the few litres sitting next to it, overheats, shuts down, cools and tries again.

Here is how we tell a failing pump from the things that merely look like one, and what you can check safely before calling a Gas Safe registered engineer.

Signs that a central heating pump is failing

Across Kent, the pumps we end up replacing almost always announce themselves first:

• Radiators lukewarm everywhere, or only the ones nearest the boiler warm up. The water is being heated but not moved.
• The boiler fires, runs for a minute or two, cuts out and repeats. With no flow it hits its overheat limit quickly.
• The pump body is too hot to rest your hand on. A warm pump is normal; a scorching one is not.
• A hum or buzz with no vibration. The motor is being fed power but the rotor is not turning.
• Grinding, rattling or a rhythmic knock. Worn bearings, or the impeller chewing through debris.
• Hot water works, heating does not, and turning the room thermostat up changes nothing. On a system with a cylinder this points at the pump or a motorised valve; we cover the valve side in hot water but no heating.

None of these alone is proof. Two or three together usually is.

Why is my central heating pump so hot?

A running pump is meant to be warm. It is a motor sitting in a pipe full of hot water, so it takes on that temperature and adds a little of its own. What is not normal is a pump noticeably hotter than the pipe either side of it, or one that is hot while the heating is supposedly off.

The usual cause is a rotor struggling to turn. Sludge in the system, a partly seized shaft or an impeller jammed by a flake of magnetite all make the motor work harder than it was designed to, and that effort turns into heat. Left alone, the winding fails and the pump goes silent for good.

Why is my central heating pump noisy?

Pump noise tells you something specific, which is why we ask about it on the phone:

• Humming or buzzing, nothing else. Power is reaching the motor but the rotor is stuck. On older pumps with a large slotted screw in the centre of the head an engineer can sometimes free it; on modern sealed pumps it usually means replacement.
• Gurgling, like a rushing stream. Air trapped in the pump head. Bleeding the radiators does not always clear it.
• Grinding or a loud rattle. Bearings on the way out. This one does not recover.
• A whine that changes pitch as the system warms. Often cavitation - the pump pulling water faster than the system can supply it, usually because the speed is set too high or the pressure is low. Check the gauge before blaming the pump.

Our boiler noise guide covers sounds from the appliance itself.

Central heating pump running but radiators cold

The pump feels warm and you can hear it, yet the house is cold. Three things we find on these jobs:

1. The rotor turns but does not shift water. A worn impeller spins freely and pumps almost nothing. The only way to be sure is to isolate and open it, which is an engineer’s job.
2. The pump is fine and the system is blocked. If the bottoms of your radiators are cold while the tops are hot, read radiator cold at the bottom first. A new pump forced through a sludged system fails young, and we would rather talk to you about a power flush than fit the same pump twice.
3. The pump is on the wrong speed. Three-speed pumps knocked down to setting one keep the nearest radiators warm and starve the rest.

Why does my central heating pump keep running?

Usually because it is supposed to. Most boilers use “pump overrun”: when the thermostat is satisfied and the burner shuts down, the pump carries on for a few minutes to carry the last of the heat away so the boiler does not overheat. Two or three minutes of running after the heating stops is normal.

A pump that runs all night with the programmer off is different. That is normally a stuck relay on the boiler’s circuit board, a wiring centre fault or a thermostat calling for heat when it should not. The pump itself is rarely the faulty part.

How to check a central heating pump is working

These checks are safe for a householder. None involve opening a boiler or touching mains wiring.

• Find it. On a regular or system boiler with a cylinder, the pump is usually in the airing cupboard or beside the boiler: a squat metal cylinder with a pipe in and out. On a combi it is inside the case. Never remove a boiler case; that is for a Gas Safe registered engineer only.
• With the heating on, rest a hand on the pump body. You should feel a faint, steady vibration and hear a low, even hum. Silence, or a hum with no vibration, means it is not turning.
• Check the pressure gauge on a sealed system. Our boiler pressure guide explains what it should read.
• Check the isolating valves either side of the pump are open. A slot in line with the pipe is open; across it is closed.
• Look at the speed setting and make sure nobody has turned it right down.
• Confirm the controls are actually calling for heat - programmer on, thermostat above room temperature.

If all of that checks out and the radiators are still cold, stop there. The next steps involve isolating electrics, draining down or opening the boiler, and that is where we come in.

How long does a central heating pump last?

There is no honest single answer. We see pumps in Kent airing cupboards that have run for well over a decade, and we replace pumps that failed young because they spent their lives grinding sludge. Dirty system water, air and blocked pipework are what shorten a pump’s life, and an annual boiler service is where we check all three.

Can central heating pumps be repaired?

Sometimes, briefly. On an older pump with a vent screw in the head we can occasionally free a seized rotor and get you through a cold snap, and some older pumps have a replaceable capacitor. But modern pumps are sealed units built to be swapped, and a pump that has seized once will seize again. In most cases the sensible answer is a new pump, ideally a modern modulating one, which uses noticeably less electricity than the old fixed-speed types and is quieter with it.

Replacing an external pump is straightforward. Inside a combi or system boiler it means working within the appliance, which must be done by a Gas Safe registered engineer. Plumbing Angels are registered under number 951167.

What happens when you call us

Our diagnostic visit is charged at £95+VAT for the first hour and £47.50+VAT for each hour after. Within that first hour we will normally have confirmed whether it is the pump, a valve, the controls or the system water, and any part is agreed with you before we order or fit it.

Cold radiators and a boiler that will not stay lit are not something to sit on once the nights draw in. Call us on 01732 792 454 or book through our boiler breakdowns and repairs page, and we will get the heat moving round the house again.