Why Is Your Water Pump Not Working? Causes, Risks and Fixes

“Not working” covers more ground than “not turning on.” A pump can fail to start at all, or it can run perfectly normally — and still not deliver water where it’s needed. Each pattern points to a different fault, and each carries a different level of risk if it is left unaddressed. Below, we break the problem into the four ways a pump typically stops working, what causes each one, and how Mawdsleys Pump Services gets it resolved. We have also created a useful tool to help you manage your pumps. Download it for free below.

Pattern 1: The Pump Won't Turn On At All

This is the simplest pattern to recognise — no hum, no vibration, nothing.

Common causes:

No power reaching the pump — a tripped MCB, a tripped RCD, a blown isolator fuse, or an isolator left switched off. BS 7671:2018+A3:2024 requires 30mA RCD protection on most outdoor and submersible pump circuits, so any earth leakage fault will trip the circuit and stop the pump (Total Skills UK, 2026).
Float switch failure — for sump, sewage and borehole storage systems, a stuck, tangled or worn-out float switch is typically the single most common reason a pump does not start.
Low water level — where dry-run protection is fitted, the pump is often designed not to start at all once the level drops below the minimum intake point. This is the protection working correctly, not a fault.

The risk:

A single RCD trip is usually harmless. A repeated trip typically signals a genuine fault such as moisture ingress or cable damage, and resetting it repeatedly can mask that fault until it becomes a fire risk or a full motor burnout. On sump and sewage systems, a float switch fault left unaddressed typically leads to internal flooding or sewage backup as water rises unchecked.

Pattern 2: The Pump Runs, But No Water Comes Out

This pattern is often more alarming than a simple no-start, because the pump sounds fine — the fault is inside the hydraulics, not the electrics.

Common causes:

Airlock — trapped air sits at the top of the pump housing, where the impeller is, and prevents it from moving water. A small air pocket is enough to stop flow almost completely, even though the motor runs normally (Waterpump.co.uk, 2025). Airlocks are more common in surface-mounted jet pumps than in submersibles, but submersible units in wells with fluctuating water levels can still be affected
Low water level / cavitation — if the static water level has dropped below the pump intake, the pump pulls air instead of water rather than failing outright. It is physically running, but producing vapour bubbles instead of flow

Clogged intake or jammed impeller — debris that bypasses the intake strainer can jam the impeller vanes; the motor keeps turning, but the hydrodynamic transfer of energy to the water stops
Failed or stuck check (non-return) valve — a check valve that has failed allows water to drain back down the pipe between cycles, so the pump has to work against an empty or partially empty column each time it starts.
Kinked, frozen or blocked discharge line — water needs a clear path out; any restriction on the discharge side can stop flow even with a fully functional pump.

The risk:

This is a high-risk pattern for the pump itself. Submersible motors rely on the surrounding water flow for cooling, so a motor running while pulling air or dry-running can overheat and suffer permanent damage within minutes to hours, not days. A pump left running in this state is one of the fastest routes to a full motor replacement.

Pattern 3: The Pump Short-Cycles — Turning On and Off Too Often

Here, the pump works, but it starts and stops every few seconds or minutes instead of running a normal cycle.

Common causes:

Waterlogged pressure tank — the number-one cause of short cycling. When the tank’s internal bladder fails, the tank loses its air cushion, can no longer store pressurised water, and the pump has to kick in almost continuously to compensate.
Faulty or clogged pressure switch — the switch that tells the pump when to start and stop can be fouled by sediment or mineral content in the water, or its electrical contacts can burn out, causing incorrect on/off signals.
Incorrect air charge in the tank — even with a healthy bladder, an air charge that has drifted from the correct pressure (typically set 2 psi below the pump’s cut-in pressure) will cause premature cycling.
A small leak in the system — a slow leak anywhere in the pipework can bleed pressure away steadily, triggering the pump to restart more often than it should.

The risk:

Short cycling is a mechanical-wear problem rather than an immediate safety issue, but it is a serious one. Each start draws a current surge, and motors are only designed for a finite number of starts; short cycling can add hundreds of extra starts a day, which typically leads to overheating and a motor burning out well before the end of its expected life.

Pattern 4: The Pump Runs Continuously, or Delivers Weak Flow

The pump never seems to switch off, or the flow at the tap or outlet is noticeably weaker than usual.

Common causes:

Worn impeller or stages — over time, sand, silt and abrasive minerals in the water wear down the impeller stages inside a submersible pump, gradually reducing the pressure and flow each stage can generate.

Clogged filter, strainer or discharge pipe — a partial blockage anywhere in the system reduces flow without stopping it entirely.
Undersized pump for the demand or depth — a pump correctly sized when installed can become inadequate if household or site demand increases, or if the water table has dropped and the effective lift has increased.
A leak downstream — continuous running with falling pressure often means water is escaping the system somewhere before it reaches the outlet.
Failed Stop Float – the stop float fails and the pumps keeps running even after the sump has emptied. This then pulls in air and damages seals within the pump. The motors aren’t designed for continual use and burns out.

The risk:

Left unresolved, continuous running accelerates wear on every component — bearings, seals and windings — turning a flow problem into a full pump failure. It also typically drives a noticeable rise in energy costs, since the pump is drawing power far more of the time than it should be.