Macerator toilet problems in basement flats

Clifton and Hotwells are full of tall Georgian and Regency houses split into flats. Many have a basement or lower ground flat with a bathroom added long after the house was built. Where the toilet sits too low, or too far from the soil pipe for waste to fall naturally, a macerator toilet is often fitted. It chops waste and pumps it up a small pipe to the drain. When it works, you forget it is there. When it fails, it fails fast.

How a macerator works

A macerator sits behind or beside the toilet pan. When you flush:

1. waste and water flow into the unit
2. a pressure switch senses the water level and starts the motor
3. blades break the waste down
4. a pump pushes it up a narrow pipe to the soil stack or drain
5. a non return valve stops it running back

Because the pipe is small and the motor works hard, these units are less forgiving than a normal toilet.

Common problems and causes

Symptom	Likely cause
Motor runs but water does not go down	Blockage in the outlet pipe or a jammed blade
Humming with no pumping	Jammed blades, often from wipes or hair
Unit starts by itself every so often	Leaking cistern or a failing non return valve letting water fall back
Motor runs on for a long time	Scaled or stuck pressure switch, or a partial blockage
Water rising in the shower tray or basin	Shared unit backing up from a blockage
Bad smell	Waste left in the unit, or a failing seal or vent
Loud grinding	Something hard in the blades, such as a cotton bud, a bottle top or a toothbrush

Why hard water matters

Bristol Water says its water is moderately hard to very hard. Limescale builds up inside a macerator over time. It coats the blades, the chamber walls and the pressure switch. A scaled switch can stick on or off. Manufacturers usually sell a descaler made for their units, and in a hard water city it is worth using on the schedule they suggest.

What never to flush

Most macerator failures in Clifton flats come from the wrong thing being flushed. This is especially common in rented flats and short lets, where guests do not know the toilet is pumped. Put a clear sign in the bathroom.

Never flush:

• wet wipes, even ones sold as flushable
• sanitary products or nappies
• cotton buds, cotton pads or dental floss
• kitchen roll or tissues
• cooking fat or food
• strong drain chemicals not approved for macerators

What you can safely check

1. Turn off the power. Macerators are wired to a fused spur nearby. Switch it off before you remove any cover.
2. Check the cistern. If the toilet cistern is leaking into the pan, the unit keeps starting. Our guide on a toilet that keeps running covers the fixes.
3. Look for the obvious. If you know a wipe or object went down, tell the plumber. It saves time.
4. Do not plunge it like a normal toilet. Forcing water into the unit can push waste into the motor or the shower waste.

Do not open the unit itself unless you know what you are doing. It holds dirty water and has electric parts.

When it needs a plumber

Call a plumber if:

• the unit hums but will not pump
• water is backing up into a shower or basin connected to the unit
• the motor runs on for long periods
• there is a smell you cannot trace
• the unit is old and keeps failing

A visit usually means draining and opening the unit, clearing blades and outlet, cleaning or replacing the pressure switch and non return valve, and checking the discharge pipe. If the outlet runs a long way or climbs high to reach the soil stack, the pipe itself can be the weak point.

Our tap and toilet repairs page explains how repair visits work.

Keeping a macerator healthy

A few habits help a macerator last:

• descale it on the schedule the manufacturer suggests, using its approved product
• flush with plenty of water and do not leave waste sitting in the unit
• check the cistern does not leak into the pan, as constant starts wear the motor
• keep the area round the unit dry and the access panel easy to remove
• book a check if the motor starts sounding different

Clifton flats: rules and shared drains

Clifton is part of the Clifton and Hotwells conservation areas, and many of its houses are listed. Bristol City Council’s conservation area guidance explains there are stricter planning controls. If replacing a macerator means moving pipework on a front or visible wall, or cutting into historic fabric in a listed building, check with the council before work starts.

Building Regulations also apply. Approved Document H, which covers drainage in England, treats pumped WCs as an option where a normal gravity connection is not practical, and sets conditions on their use. A plumber should check whether a gravity connection is possible before replacing like for like.

The drain the macerator pumps into may be shared with the flats above. If several flats have slow drains at once, the problem is likely in the shared soil stack or drain, not your unit. Wessex Water explains which pipes are yours on its sewer pipe responsibility page. Our guide to Clifton covers more on plumbing in its older houses.