Pressure and flow are not the same
Plumbers talk about pressure (the force pushing water through the pipes, measured in bar) and flow (how much water comes out, measured in litres per minute). You can have good pressure but poor flow – for example, if a pipe is partly blocked – or reasonable flow from a low-pressure tank-fed system. Testing both helps a plumber pinpoint the problem.
Is it one tap or the whole house?
If only one tap or shower is weak, the problem is likely local: a blocked aerator or shower head, a scaled cartridge, a partly closed isolating valve or a kinked flexible connector. If every tap is weak, the cause is more likely the incoming supply, the stopcock or the hot water system.
- Clean the tap aerator or shower head, especially in hard water areas
- Check isolating valves under sinks and on showers are fully open
- Make sure the stopcock is fully open – it may have been partly closed during a previous repair
- Ask neighbours if their pressure has dropped too – it may be a supply problem
Tank-fed systems and weak showers
If your hot water comes from a cylinder fed by a cold water tank in the loft, the pressure at the shower depends on how high the tank is above the shower head. In many homes that's not much, so the shower is weak by design. A shower pump or power shower is the usual answer – but never on a combi boiler or mains supply.
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Supply pipe and water company issues
Old lead or galvanised supply pipes can corrode and narrow inside, reducing flow. A leak on the supply pipe can also reduce pressure. If the problem is in the street – maintenance work, a burst main, or supply problems at peak times – contact your water company.
What a plumber can do
A plumber can measure pressure and flow at the stopcock and at individual outlets, find blockages, replace scaled parts, renew an old supply pipe, fit a shower pump to a suitable system, or recommend changes to the hot water system. They'll also check whether your boiler or cylinder can deliver the flow you need for the showers and taps you want.
