First, is it one tap or the whole house?
This single question narrows it down fast. If only one tap or shower is weak, the problem is local to that outlet: a partly closed isolation valve, a blocked aerator or filter on the tap or shower head, or a worn cartridge. If the whole house is weak, the cause is upstream and affects the supply into the property.
Quick checks you can do yourself
For a single weak outlet: unscrew the aerator on the end of the tap or the shower head and check it for limescale and grit, which is a very common and easy fix in hard-water areas. Check the isolation valve under the sink is fully open (slot in line with the pipe).
For the whole house: check your main stopcock, usually under the kitchen sink, is fully open, as a partly closed stopcock throttles the whole supply. If you are on a combi boiler, low pressure at the hot taps specifically can be a boiler or diverter issue rather than the mains.
Causes that need a plumber
If the checks above do not fix it, the likely causes need a professional: a failing pressure-reducing valve, a hidden leak somewhere in the pipework, old and partly furred-up pipes restricting flow, or a shared supply issue. A combi boiler that gives good cold pressure but weak hot flow can also point to a fault inside the boiler.
Some of these overlap with a supply problem from the water company, which is worth ruling out by asking neighbours if theirs is low too. If it is only your house, it is yours to fix.
Getting to the bottom of it
Low pressure that you cannot trace to a simple blocked aerator or a half-shut valve is worth having a plumber diagnose, because chasing it blind wastes time and a hidden leak only gets worse. LMB covers plumbing and pressure problems across Bridgend, the Vale and South Wales. Tell Lloyd whether it is one tap or the whole house and he can point you at the likely cause before any visit.
