Signs to look for
- Weak flow at every tap, or only at some
- Hot water weak but cold water fine, or the other way round
- Pressure that drops at busy times of day
- A sudden drop in pressure, which can point to a leak
What to do first
Check the stop taps are fully open
Thames Water’s first check: turn the inside stop tap anti-clockwise to make sure it is fully open, then check the outside stop valve too. Work under the sink can leave one partly closed.
Ask your neighbours
If neighbours have the same problem, it may be the network. Check your water supplier’s website for work or incidents near your postcode.
Test the cold kitchen tap
This is usually fed straight from the mains. If it runs well but other taps or the shower do not, the problem is inside your plumbing.
Compare hot and cold
If only the hot is weak, the hot water system is the likely cause. That depends on whether you have a combi boiler, a cylinder or a tank in the loft.
Do not adjust or open up a boiler, hot water cylinder or pressure valves on unvented systems. These are safety-critical. Cleaning limescale from a tap tip or shower head is fine.
Possible causes
These are common causes, not a diagnosis. The actual fault is confirmed on site.
Partly closed valve
A stop tap or isolating valve left partly closed restricts flow to the whole house or to one fitting.
Peak demand or network issue
Thames Water notes pressure is often lower at busy times. Network problems affect neighbours too.
Leak on the supply pipe
A leak between the boundary and the house can lower pressure. Thames Water lists it as a sign of a leak.
Limescale
Scale builds up in tap tips, shower heads and valves, especially in hard-water areas.
Hot water system design or fault
Tank-fed systems run at lower pressure by design. Combi boilers have a limited flow rate. Faults in valves or cylinders can reduce flow further.
Shared or undersized supply pipe
Older properties may share a supply with neighbours or have a narrow supply pipe.
How WHP would assess it
- Measure the incoming pressure and flow where practical, to see whether the supply or the plumbing is the limit.
- Check valves, the stop tap and the route of the supply pipe.
- Work out what type of hot water system you have and whether it is working as designed.
- Explain the realistic options, which may be as simple as a valve or a scaled fitting.
We explain any call-out or diagnostic charge before booking, and agree the repair and its cost with you before carrying it out.
What affects the price
Every repair is different, so we do not publish fixed prices for this work. These are the things that make the most difference:
- Whether the cause is a single fitting or the supply into the property
- Type of hot water system
- Access to the stop tap, supply pipe and valves
- Whether parts or pipework need replacing
Before you call
Useful to send us
- Which taps or showers are affected, and hot, cold or both
- Whether neighbours have noticed the same
- Whether it was sudden or gradual
- Your boiler or cylinder type if you know it, with a photo
Get professional help when
- The pressure dropped suddenly, which may be a leak
- The stop taps are fully open, neighbours are fine and the problem persists
- Only hot water is weak and getting worse
- You are considering a pump. Get advice first.
Common questions
Who do I call: the water company or a plumber?
Thames Water advises that if neighbours have the same problem, it may be the network, so contact your water supplier. If your neighbours are fine and the cold kitchen tap is fine, the problem is inside your plumbing, so call a plumber or your landlord.
Will a pump fix it?
Sometimes, but not always, and pumps connected to a mains supply are restricted under water fittings regulations. A pump also will not fix a leak or a partly closed valve. Find the cause first.
Why is only my shower weak?
Often scale in the shower head or mixer valve, or the shower being fed differently from the taps. Clean the head first. If that does not help, the valve or supply to the shower needs checking.
Sources
Safety and responsibility details checked against these sources on 12 October 2026. Water supplier guidance can change. Check your own supplier’s current advice.