Grundfos Shower Pump Not Working — Troubleshooting Guide
Check the steps below first — if you're not confident, get it fixed safely today.
Post a job — we'll find you an engineer →Grundfos pumps must not be run dry. Isolate at the fused spur before any inspection. The pump body can become very hot during operation — allow to cool before touching.
A Grundfos shower pump that's lost its flow, won't start, or is making odd noises can be incredibly frustrating — especially when you're relying on it to get decent pressure from a cold water tank. These pumps are robust workhorses found in thousands of UK homes, but they do occasionally develop issues, often simple ones you can spot yourself before calling an engineer. Most problems stem from airlocks, blocked strainers, or isolation valves accidentally left closed — things that don't require a replacement part. This guide walks through the most common faults, what's causing them, and how to get your pump running again safely. If you're confident with basic isolation and checks, many fixes take less than an hour; however, if the pump is overheating repeatedly or making grinding noises, professional help is worth considering to avoid further damage.
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Most likely cause & what to check
Grundfos (uk.grundfos.com) is a Danish manufacturer with a strong UK presence. Their domestic shower pump range includes the SB series — the SB3-45A and SB5-45A are commonly found in UK homes. Technical data sheets and installation manuals are available on the Grundfos UK product pages.
No flow or pump fails to start: check both isolation valves are open, the fused spur is on, and the cold water tank is not empty. Grundfos SB pumps are positive head units and require a minimum head of water to start — typically 300mm between the tank and the shower outlet.
Pump runs but no or very low flow: likely an airlock. Grundfos recommend isolating the pump, slowly opening the bleed screw (a small brass screw on the pump body on some SB models) or undoing the inlet unions to purge air before restarting.
Pump overheating and cutting out: check the inlet strainers and ensure both isolating valves are fully open. Grundfos SB pumps have a thermal overload protector — if it trips, the pump will restart automatically once cooled (usually 15–20 minutes). Repeated tripping suggests a blockage or failing motor.
Unusual noise: a high-pitched whine often indicates cavitation (air ingestion) — check tank level and inlet pipework. A grinding or rattling noise suggests the impeller is damaged, possibly from being run dry, and the pump will need replacing.
Grundfos UK technical support can be reached via uk.grundfos.com — they also have a partner installer network. Replacement parts for SB pumps are widely available from plumbers' merchants including Plumb Center, Wolseley, and BSS.
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Frequently asked questions
Why has my shower pump suddenly stopped working?
The most likely culprits are an airlock in the system, an isolation valve accidentally closed, or the cold water tank running empty. Before assuming the worst, check both isolation valves are fully open, the tank has water in it, and the electrical fused spur is switched on. These three things cause the vast majority of no-flow problems and take seconds to verify.
Can I run a shower pump without water in the tank?
No — running a shower pump dry will damage the impeller and motor very quickly, and Grundfos specifically warn against this. If the tank is empty or the pump runs with no inlet pressure, stop it immediately and allow it to cool before investigating the water supply issue.
My pump is making a high-pitched whining noise — what does that mean?
A high-pitched whine almost always points to cavitation, which is air being drawn into the pump inlet. Check the cold water tank level is adequate and inspect the inlet pipework for loose connections or damage that might be letting air in; tightening a union or topping up the tank usually solves it.
How long should I wait if my pump keeps shutting off?
Grundfos pumps have a built-in thermal overload protector that resets automatically after 15–20 minutes of cooling. If it's tripping repeatedly, the pump is working too hard — usually because a strainer is blocked or an isolation valve is partially closed — so don't just keep restarting it; investigate the cause first.