Macerator Toilet Backing Up or Not Pumping? What to Do Now

If your macerator toilet is backing up, not pumping or running without stopping, stop flushing it and stop using any shower, basin or washing machine that drains into the same unit. Then switch the unit off at its fused spur before anyone touches it. A macerator is a pump with a blade, sitting in a small box behind the toilet, and nearly every fault comes down to something jamming the blade, scale on the switch, or a blocked outlet pipe.

How a macerator toilet works, and why it fails

A macerator unit collects waste from a toilet, cuts it up and pumps it through a narrow pipe to a soil stack or drain that may be some distance away or higher up. It exists because the toilet is somewhere a normal gravity drain cannot reach, such as a basement, a loft or a room added under the stairs.

That design makes it far less tolerant than an ordinary WC. The outlet pipe is much narrower than a 100mm soil pipe, the blade is small, and the pressure switch that tells the motor to start is sensitive to scale. Anything that would pass through a gravity toilet without trouble, such as a wipe, dental floss or a sanitary pad, can stop a macerator in one flush.

Common symptoms and what usually causes them

The symptom is usually enough to point to the cause. A unit that hums but does not pump is jammed. A unit that runs non-stop or starts on its own has a switch or valve fault. Water backing up into a shower tray means the unit or its outlet is not discharging.

• Humming, grinding or clicking, but the bowl does not empty. Something is wrapped around or jammed in the blade. Wipes, hair, floss and sanitary items are the usual culprits.
• Motor runs for a long time or keeps cutting in. Often a failed non-return valve, which lets water run back into the unit after each pump, or scale on the pressure switch.
• Unit does nothing at all. Check the fused spur and the consumer unit first. If power is on and there is still nothing, the switch or motor has probably failed.
• Waste coming up in a connected shower or basin. The macerator is not emptying, either because it is jammed or because the pipe it pumps into is blocked further on.
• Bad smell around the unit. Usually waste sitting in the unit because it is not pumping fully, or a small leak from the lid seal or outlet connection.

What you can safely check yourself

You can check power, stop using the unit and look for obvious leaks. Opening the unit is a different matter: it contains sewage and a cutting blade, and on many models the lid is sealed.

Switch the unit off at the fused spur before doing anything else, even if you only plan to look. Check whether the spur fuse or a breaker at the consumer unit has gone. If the breaker trips again when you reset it, leave it off, because that points to water in the motor or an electrical fault. Chemical drain unblockers and bleach should not be poured into a macerator; they can damage the seals and membranes and make the unit more dangerous for whoever opens it. The manufacturer's own descaler, used as the instructions say, is the only chemical most makers approve.

If you have another toilet in the property that drains by gravity, use that one until the macerator is sorted. Building Regulations guidance expects a macerator WC to be backed by at least one ordinary gravity-draining toilet in the building, so most homes have one somewhere.

Macerator fault or drain blockage: who to call

If the fault is inside the unit, such as a failed motor, switch, valve or seal, call a plumber or the manufacturer's service engineer. If the unit is working but its outlet pipe or the drain it discharges into is blocked, that is a drainage job.

It is worth being honest about this, because a drainage call-out is the wrong answer to a failed pressure switch. A drainage engineer can clear a jammed discharge pipe, rod or jet the soil stack or drain downstream, and camera-check the run, which is what you need when the unit is pumping against a blockage. Our blocked toilet and internal drain clearance covers that side. Replacing a motor or rebuilding the unit is parts work for a plumber who carries spares for your make.

A quick test helps you decide. If the motor runs normally and you can hear it pumping, but the level in the connected shower or basin still rises, the problem is downstream of the unit. If the motor hums, grinds or stays silent, the problem is in the unit itself.

When a blocked macerator needs attention tonight

It is urgent when it is the only working toilet, when waste is overflowing into a shower tray or across the floor, or when the unit has leaked near sockets or electrics. Otherwise it can usually wait until the morning with the unit switched off.

Basement flats in London often have a macerator as their only toilet despite the guidance, and in that case a household with no working toilet overnight is a genuine emergency. If sewage has come up through a shower or floor drain, our guide to sewage coming up through a drain or toilet covers the safety steps. Our rates are set by the clock: 7am to 5pm is the standard rate, 5pm to midnight the evening rate, and midnight to 7am the night rate, with current figures on the pricing page and the price agreed before anyone travels.

Keeping a macerator working

Only toilet paper and human waste should go into a macerator. Everything else, including so-called flushable wipes, is the most common reason we see these units blocked.

Put a small bin and a clear note next to the toilet, particularly in a rental, a guest room or anywhere children use it. Descale it periodically with the manufacturer's product if you are in a hard water area, which covers most of London, and have it serviced if it starts running longer than it used to. A unit that takes longer to pump each week is warning you before it fails outright.