QUESTIONS
Why won't my shower pump start?
Updated 07/26
By: Alex Peters
Reviewed: Content Team
A shower pump that won't kick in is almost always one of a small handful of causes, and most are quick to check yourself before assuming the pump itself has failed. Here's what to check, in the order that's quickest to rule out.
The quickest checks to run first
Why airlocks and blockages stop a pump starting
What a flow switch does, and why it fails
Why installation height matters for some pumps
How to bleed or reset a stuck pump
When it's time to call a plumber
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Check the basics first
1. Power supply
Before anything plumbing-related, confirm the pump is actually getting power. Check the isolator switch is on, look for a tripped fuse or circuit breaker, and make sure nothing's been accidentally switched off at the consumer unit. This takes seconds and rules out the simplest cause first.
2. Overheating or dry-run protection
Many pumps have a built-in thermal cutout that shuts the pump down if it overheats or runs dry, and won't restart again until it's cooled. If the pump's been working hard, running with low water, or has recently tripped, give it 20-30 minutes to cool before assuming it's actually broken.
If the pump hums but doesn't fully start, that's often a different fault (commonly a failing capacitor) rather than a flow or blockage issue, and is worth mentioning specifically if you do end up calling a plumber, since it narrows down the cause.
Common plumbing causes
The pump is running dry
A blockage anywhere in the inlet or outlet pipework can stop water reaching the pump properly. This can also trip the pump's safety cutout and stop it working until it's reset.
Airlocks
Trapped air in the system is one of the most common causes of a shower pump not starting, or pulsing on and off. The fix is usually to bleed the shower pump, which clears the trapped air and restores normal flow.
Blocked pump filter
Limescale, mineral deposits, or general debris from the pipework can clog the pump's filter over time. Clean it out and refit it, and check whether this resolves the problem before looking further.
Faulty or stuck flow switch
Most shower pumps rely on a flow switch to detect when water is moving and trigger the pump to start. If the switch is worn, stuck, or fitted with a non-return valve (NRV) that's seized, the pump may never receive the signal to switch on, even with no blockage or airlock present. This is a common failure point on older pumps and, unlike a blockage or airlock, usually needs a replacement part rather than a DIY fix.
If your shower has stopped working after a recent shower valve or unit change rather than gradually, the new valve's internal non-return valves can sometimes restrict flow enough to stop the pump triggering. Worth mentioning to whoever fitted it if the timing lines up.
Not enough installation height (positive head pumps)
If your pump is a positive head type (relying on gravity from a cold water tank above it), it needs a minimum vertical distance between the tank and the pump to build enough pressure to trigger reliably. If a pump has recently been moved, or a new shower unit sits differently to the old one, insufficient height can be the reason it won't start, even though nothing is actually broken. This is a plumbing design issue rather than something you can easily fix yourself.
How to fit a new shower pump
If your pump genuinely needs replacing rather than repairing, our step-by-step guide to fitting a shower pump covers the process, including:
Checking safety regulations
Connecting the pump to the electric supply
Isolating the water supply
Fitting a flange
Using flexible hoses
Flushing the pipework
Turning on the power and testing
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Hire a local shower expert to do the job
If you've worked through the checks above and the pump still won't start, it's time to bring in a professional rather than keep guessing.
How to bleed a shower pump
Are you having problems with your shower pump? Strange noises, fluctuations in temperature or pulsing when in use? If this all sounds very familiar, you might want to try bleeding your shower pump to see if it can resolve the problem.
Before you call a plumber
Frequently asked questions
This usually points to an electrical fault, often a failing capacitor, rather than a blockage or airlock. It's worth flagging this specific symptom to a plumber, since it changes what they'll check first.
Checking power, bleeding for airlocks, and cleaning the filter are all reasonable DIY steps. A faulty flow switch, seized non-return valve, or installation height issue is better left to a professional.
New shower valves and mixers have their own internal non-return valves, which can sometimes restrict flow enough to stop a pump's flow switch triggering. Worth raising with whoever fitted it if the timing matches up.
Give it around 20-30 minutes to cool before trying again. If it still won't start after that, the cause is likely something else.
Flow switches themselves are generally inexpensive parts, though labour and access can add to the cost depending on how the pump is installed.
Positive head pumps do, since they rely on gravity from the tank above to trigger reliably. Negative head pumps are designed differently and don't have the same requirement, so it depends on which type you have.
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