My Saniflo is humming but not draining. What does that mean?

The motor is running but the blades cannot turn or the outlet cannot pass water, and the smart money is on wipes wound around the macerator. Switch it off at the wall or the fused spur before anything else. Running a jammed motor is how a blocked Saniflo becomes a dead one.

Can I put a plunger down a macerator toilet?

No, and this is a genuine safety line rather than us protecting our trade. A macerator is a sealed unit with rotating blades and a mains electricity supply, usually sitting in a wet room. Plunging can force water into the unit's electrics, and opening the case yourself puts your fingers where the blades live. Kill the power and stop there.

Is it the Saniflo or the pipe behind it?

A useful tell: if the unit runs, empties, then the waste backs up again minutes later, the macerator is probably fine and the small-bore discharge pipe beyond it is blocked or scaled. If the unit hums, trips the electrics or does nothing at all, the problem is in the box. We check both rather than guessing, because replacing a healthy unit to fix a scaled pipe is an expensive way to learn the difference.

What does a call-out cost?

Macerator and small-bore blockages sit in our blocked toilet and sink work: most jobs run £80 to £160, out of hours from £150, agreed before we start. If the unit itself has died rather than jammed, we will say so plainly and you will not pay twice for one problem.

How-to

Saniflo Blocked? What You Can Fix Yourself, and Where the DIY Ends

Saniflo humming but not draining, or tripping the fuse? What the sounds mean, the safe checks you can do, and the hard line where DIY stops.

Published 15 August 2026

A Saniflo is what makes the basement loo, the loft en-suite and half of Brentford’s new-build bathrooms possible: a macerator that shreds waste and pumps it through a narrow pipe to wherever the real drains are. When it works, nobody thinks about it. When it stops, it stops a whole bathroom, and it usually announces the fact with a noise.

The noise is diagnostic, so start there.

Translate the noise

Humming, not draining. The motor is running against blades that cannot turn. Nine times out of ten something is wound around the macerator, and that something is usually wipes. Switch off the power now, at the plug or the fused spur. A motor left humming against a jam cooks itself, and then a £100 unblock becomes a new unit.
Silence. No hum at all means no power or a dead motor. Check the obvious without opening anything: the switch, the fuse in the spur, the RCD. If power is present and the unit is silent, the motor has likely retired.
Runs, empties, backs up again minutes later. This one is the impostor. The macerator is probably healthy and the small-bore pipe after it is the problem, narrowed by limescale (south-west London water is generous with it) or blocked further along. People replace perfectly good units over this. Diagnose before spending.
Tripping the electrics. Water has got somewhere it should not be. Leave the power off and stop here.

The hard line

Here is where we are dead straight, because this is a safety boundary and not a sales pitch: a macerator is a sealed unit containing rotating blades, connected to mains electricity, in a wet room. The DIY that is safe is switching it off, checking the fuse, and not flushing again. The DIY that is not safe is plunging it, opening the casing, or fishing around the inlet. Nothing about a bathroom emergency is improved by fingers meeting blades.

(We say this as people who genuinely enjoy dismantling a jammed macerator. It is a satisfying puzzle. With the power isolated and the right kit, it is also a quick one.)

Why wipes are almost always the villain

A normal toilet on a 100mm gravity pipe can sometimes get away with the odd “flushable” wipe. A macerator cannot get away with any. Wipes do not break down; they wrap. Around blades, they wind into a rope, and a rope around a rotor is a jam every time. In the Brentford towers we see this at scale: one flat’s wipe habit, one communal pump-out, everyone’s morning ruined. If a Saniflo lives in your house, the rule is paper only, and the rule has no exceptions it will forgive.

What we actually do

Power isolated, unit opened properly, jam cleared, blades checked, then the part most people skip: we look at the discharge pipe too, because a unit that jammed once on a scaled, narrowed pipe will jam again soon. Most blocked toilet and macerator jobs run £80 to £160, out of hours from £150, price agreed before we start. If the motor has genuinely died, we will tell you it is a replacement rather than pretending a clear will save it.

One prevention habit worth the thirty seconds: run the unit with clean water regularly if the bathroom is rarely used. A macerator that sits dry for months seizes out of pure boredom, and no bathroom deserves that.