Summary

A shower pump boosts flow on a gravity-fed system by drawing stored water from a cold water storage cistern and a vented hot water cylinder and pushing it to the shower outlet with more force than gravity alone provides. It is a mechanical device with a motor, an impeller (or two, on twin-impeller models), and — depending on whether it's a positive or negative head installation — either a flow switch or a pressure-sensing switch that detects demand and starts the pump. "Not working" covers two genuinely different faults that need to be told apart immediately on site: the pump not starting at all, and the pump running but not delivering usable flow.

This is a distinct fault category from an electric shower not working. An electric shower heats mains-fed water instantaneously inside its own sealed unit and is diagnosed around its heating element, solenoid, and thermal cutout — see electric shower not working for that fault tree. A shower pump, by contrast, boosts already-tempered water from a stored hot and cold system and has no heating element of its own; the fault categories, components, and diagnostic sequence are entirely different even though both ultimately present to the customer as "no shower" or "weak shower."

This article covers the diagnostic sequence for both "won't start" and "runs but no delivery" faults, the electrical and water regulations relevant to pump installation and repair, and when a fault points to replacement rather than repair. For noise and vibration complaints specifically (a pump that runs and delivers water but sounds wrong), see shower pump noisy vibrating; for full installation guidance see shower pump installation and pump selection.

Key Facts

Quick Reference Table

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Symptom Most likely cause Fix
Pump completely silent, no response when shower turned on No power — check fused spur, RCD, isolator Test supply with voltage tester; reset/replace as needed
Pump hums but doesn't start turning Seized impeller/bearings, or failed capacitor Attempt manual free (if fitted); test capacitor; replace as confirmed
Pump runs briefly, then stops and won't restart Dry-run/thermal cutout tripped — inlet starved Check cistern level, strainer, and isolation valves before assuming pump fault
Pump runs continuously but no water at shower head Airlock, closed isolation valve, or blocked strainer Bleed/prime per manufacturer procedure; check all valves fully open
Pump runs, weak flow only Partially closed valve, partially blocked strainer, or low cistern Check valves and strainer; check cistern fill rate
Pump runs on cold side only / hot side only Fault isolated to one impeller (twin-impeller models) or that side's feed/flange Check flange and feed on the affected side before condemning whole pump
Pump won't start, negative head installation Faulty/misadjusted pressure switch or vessel Test and replace pressure-sensing switch
Pump won't start, positive head installation Flow switch failed to detect demand Test flow switch continuity/operation
No power at all reaching the fused spur Upstream circuit fault, or pump accidentally isolated during other works Trace circuit back to consumer unit; check nothing else was switched off
Pump trips the RCD immediately on power-up Motor winding fault, water ingress to motor housing Isolate and do not reset repeatedly — investigate before re-energising

Detailed Guidance

Step 1: Confirm which fault category this is

Shower pump not working
├── Is this a mechanical booster pump, or an electric shower unit?
│     └── Electric shower → wrong article, see [electric shower not working](/knowledge/fault-finder/electric-shower-not-working)
│
├── Does the pump run AT ALL when demand is triggered
│     (tap/shower turned on, or for negative head, pressure switch triggered)?
│     ├── NO — pump silent or humming only → "won't start" branch
│     └── YES — pump audibly runs → "runs but no delivery" branch

Step 2: "Won't start" diagnostic tree

Pump won't start
├── Check power reaches the pump
│     ├── Fused spur switched off / MCB or RCD tripped at consumer unit
│     │       → Reset once; if it trips again immediately, isolate and
│     │         investigate before repeated resetting (motor/water ingress risk)
│     └── Confirmed voltage present at pump terminals → proceed
│
├── Pump hums but rotor doesn't turn
│     ├── Try the manual release/nudge point on the motor shaft, if fitted
│     │       (frees a seized impeller after a period of disuse)
│     └── Test run/start capacitor — a failed capacitor causes exactly
│           this symptom on single-phase motors
│
├── Pump completely silent with power confirmed present
│     ├── Positive head → test the flow switch for continuity when
│     │       flow is simulated
│     └── Negative head → test the pressure-sensing switch/vessel;
│           check its calibration/adjustment against manufacturer spec
│
└── Pump starts, runs briefly, then stops and won't restart
      → Dry-run/thermal cutout has tripped
      → Check BEFORE assuming pump fault:
            - Cold water storage cistern level and fill rate
            - Inlet strainer for blockage
            - Both hot and cold isolation valves fully open
      → If inlet supply confirmed healthy and cutout still trips,
        the cutout itself or the motor may be at fault

Step 3: "Runs but no delivery" diagnostic tree

Pump runs but no/weak water delivery
├── Check ALL isolation valves (hot in, cold in, outlet) are FULLY open
│     — a valve left partially closed after other plumbing work is one
│     of the most common causes of this exact symptom
│
├── Check inlet strainer(s) for blockage
│     → Isolate, remove, clean or replace
│
├── Attempt to bleed/prime the pump per manufacturer procedure
│     (open valves slowly, allow air to purge for ~30 seconds, restart)
│     ├── Resolves it → airlock confirmed
│     └── Air returns quickly / won't clear
│           → Check Surrey/York or Essex flange fitted correctly on
│             the hot cylinder take-off — a missing/incorrect flange
│             lets the pump draw air down the vent continuously
│
├── Fault isolated to hot side only or cold side only (twin-impeller)
│     → Check that side's flange, strainer, and feed independently
│     → Do not condemn the whole pump for a single-side fault
│
└── All of the above checked, still no delivery
      → Check non-return valves aren't stuck closed
      → Test cistern fill rate under simulated demand — an undersized
        or slow-filling cistern can appear to starve a healthy pump

Testing the flow switch (positive head)

  1. Isolate power. Access the switch, usually a small paddle or diaphragm device on the pump's inlet or a dedicated flow sensor in-line just ahead of the pump.
  2. With power isolated, manually actuate the switch (where accessible) and test for continuity with a multimeter.
  3. If no continuity when actuated, replace the switch matched by part number.
  4. Reassemble, restore power and water, and test by opening the shower valve to trigger genuine flow demand.

Testing the pressure switch/vessel (negative head)

  1. Isolate power. Locate the pressure switch or small pressure vessel, typically mounted on the pump body or immediately adjacent.
  2. Check the switch's calibration/adjustment screw against the manufacturer's setting — a switch adjusted too high or too low for the installation's actual head can fail to trigger reliably even when mechanically sound.
  3. Test for continuity when pressure is manually applied (where the design allows), or substitute a known-good switch if uncertain.
  4. Replace if faulty, reconnect, and test with genuine demand at the shower valve.

Flow/pressure switch replacement typically costs £25–£60 in parts and 30–60 minutes labour.

Clearing a seized pump after disuse

  1. Isolate power and water. Check the pump body for a manual release point on the motor shaft (a small slotted end accessible with a flat screwdriver on many domestic pump models).
  2. Gently rotate the shaft by hand to free the impeller — do not force excessively; a genuinely seized bearing (rather than just a stiff, unused impeller) will not free this way and points toward pump replacement.
  3. Restore power briefly to test rotation before reconnecting to the water system fully.
  4. Flush the strainer and inlet pipework before restoring full service, since a pump left dry for a long period is often associated with a cistern that's also been low or drained, allowing debris to settle.

When to recommend pump replacement over repair

Frequently Asked Questions

How do I tell quickly whether this is a shower pump fault or an electric shower fault?

Check what's physically fitted at the shower position. An electric shower is a wall-mounted unit with its own heating element that takes a cold mains (or occasionally stored) feed and heats it on demand — diagnosed via electric shower not working. A shower pump is a separate unit, almost always sited remotely in an airing cupboard or loft, boosting already-mixed hot and cold water from stored supplies to a conventional shower valve or mixer at the wall. If there's a pump-shaped unit away from the shower itself, it's this fault tree.

The pump was working fine until other plumbing work was done elsewhere in the house — what should I check first?

Isolation valves left closed or partially closed after unrelated work is one of the most common causes of a sudden "pump not working" complaint, and it's cheap and fast to rule out before any component testing. Check every valve on the pump's hot feed, cold feed, and outlet is genuinely fully open before assuming a component has failed.

Can I just keep resetting the RCD if the pump trips it?

No — repeatedly resetting an RCD that trips on a specific appliance risks energising a fault (typically water ingress to the motor windings or an insulation breakdown) and should be treated as a stop signal, not a nuisance to work around. Isolate the pump, test the motor's insulation resistance, and identify the cause before restoring power.

Is a shower pump notifiable work under Part P?

Like-for-like component replacement (switch, capacitor, strainer) within an existing pump is not notifiable — it's appliance repair, not fixed wiring work. However, if the fault investigation reveals the fused spur circuit itself needs remedial work, or if a pump is being newly installed or the circuit altered, that work is notifiable under Building Regulations Part P and should be self-certified or notified accordingly.

The pump runs and sounds normal but the shower is still weak — is that this fault or something else?

If the pump is confirmed running and delivering some flow but performance is generally weak rather than absent, check first whether this is genuinely a pump fault (worn impeller, undersized cistern, partially blocked strainer) or a downstream issue at the shower valve/head itself (limescale in the shower head, a restrictive flow regulator, or an undersized shower hose). Don't assume the pump is the cause just because it's in the system — trace the fault to its actual source before replacing parts.

Regulations & Standards