Pressure is the force pushing water; flow is how much arrives per minute. Most complaints about pressure are really about flow. Establishing whether the problem is at one outlet or all of them, and whether the system is gravity-fed or mains-fed, narrows the cause to a short list very quickly.
Pressure and flow are not the same thing
Pressure is the force behind the water, measured in bar. Flow is the volume that actually arrives, measured in litres per minute. A hosepipe with your thumb over the end has high pressure and low flow. A wide pipe from a header tank a metre above your head has low pressure and can still have decent flow.
This matters because the fixes are completely different. If a shower is weak because the supply pipe is scaled up, a pump will not help much – there is nowhere for more water to come from. If it is weak because it is gravity-fed from a loft tank two metres above the shower head, the flow is fine but there is simply not enough pressure to drive the shower, and a pump is exactly the right answer.
So the first question is always: is the water coming out slowly and weakly, or coming out at a reasonable rate but without force? The second question is whether it is everywhere or just one place.
The diagnostic sequence
- Is it one outlet, or all of them?One outlet points at that outlet: blocked aerator, scaled shower head, partly closed isolation valve, blocked or kinked flexible tail, or a failed cartridge. Everything else is a system or supply problem.
- Is it hot only, cold only, or both?Cold only points at the incoming main or the cold distribution. Hot only points at the cylinder, the combi, or scaling in the hot side. Both points upstream of everything.
- What type of system do you have?A combi and an unvented cylinder both deliver at mains pressure. A vented cylinder with a loft tank delivers hot at gravity pressure while the kitchen cold tap is usually on the mains, which is why one is strong and one is weak.
- Is the mains itself adequate?We measure static pressure and, more importantly, dynamic flow at the stopcock. That number is the ceiling on everything downstream and it is the figure nobody checks.
- Has anything changed?A sudden drop points at a valve, a burst, a failed pressure-reducing valve or a water company issue. A gradual decline over years points at scaling or a slowly failing component.
What we actually find
| Symptom | Common cause | Fix |
|---|---|---|
| One tap poor, rest fine | Blocked aerator or scaled flexible tail | Clean or replace – minutes |
| Shower weak, taps fine | Scaled shower head or hose, or a failing thermostatic cartridge | Descale or replace the cartridge |
| All hot outlets weak, cold fine | Scaling in the cylinder coil or hot distribution, or a partly closed cylinder valve | Depends on findings – sometimes a cylinder conversation |
| Everything weak, everywhere | Mains supply restriction, a failing pressure-reducing valve, or an undersized supply pipe | Measure first. Often the supply pipe from the boundary |
| Pressure fine at night, poor in the morning | Demand on a shared or marginal main | Sometimes an accumulator is the right answer |
| Fine upstairs, poor downstairs, or vice versa | Gravity system with limited head, or badly routed distribution | Pump, or re-route |
| Got worse suddenly with no work done | Valve knocked, burst somewhere, or a water company problem | Check the neighbours first – it saves a call-out |
If the whole street has poor pressure, it is the water company and it costs you nothing to report it. This single question resolves a meaningful share of calls before anyone gets in a van.
The solutions, and when each is appropriate
Descaling and component replacement
In a hard-water county this is genuinely the answer more often than anything else. Aerators, shower heads, flexible tails and thermostatic cartridges all scale up and all restrict flow progressively. It is cheap, it is quick, and it is the first thing to eliminate.
Upgrading the supply pipe
If the incoming main is a narrow old pipe, everything downstream is limited by it. Replacing the section from the boundary to the house in a larger diameter is real work, but it is the only thing that raises the ceiling. This is frequently the honest answer when somebody wants an unvented cylinder and the mains cannot feed it.
A pump
The right answer for a gravity-fed system with adequate flow but insufficient head. Fitted correctly, with proper feeds, it transforms a weak shower. Fitted to a mains-fed system it is usually the wrong tool, and pumping directly off the mains is not permitted under the water fittings regulations in any case.
An accumulator
A vessel that stores mains water under pressure and releases it during peak demand. The right answer where flow is adequate on average but insufficient at peak – a genuinely elegant fix for a marginal supply, and much less well known than it should be.
Changing the system
Moving from a gravity system to an unvented cylinder delivers mains pressure everywhere, which solves the problem comprehensively – provided the incoming main can supply it. See unvented cylinders.
Weak shower or poor flow? We measure the actual figures before recommending anything – a pump fitted to the wrong problem is money wasted.
Questions we get asked about this
Will a pump fix my low pressure?
Only if you have a gravity-fed system with good flow and insufficient head. On a mains-fed system it usually will not help, and pumping directly from the mains supply is not permitted. Getting this wrong is the most common expensive mistake in this area.
Why is my kitchen cold tap strong and everything else weak?
That is the signature of a vented system. The kitchen cold is taken directly off the incoming main for drinking water, while everything else is fed by gravity from a tank in the loft. It is not a fault – it is how the system was designed.
My pressure got worse over several years. Why?
Almost always scaling. In hard water, the internal diameter of pipework and the orifices in fittings reduce gradually. Nothing breaks, so there is no obvious moment when it happened.
How do I know if the problem is the water company?
Ask a neighbour, and check your supplier’s website for reported issues. A whole-street problem is theirs. A single-property problem that appeared suddenly is usually a valve or a burst.
Can I have an unvented cylinder if my pressure is low?
It depends on the measured flow rate at the stopcock, not on how the shower feels. An unvented system needs a minimum flow to work properly. We measure before specifying, and if the mains cannot support it we will tell you rather than fitting one that disappoints.
What is a pressure-reducing valve doing in my house if my pressure is low?
Protecting the system from high mains pressure – but they do fail, and a failed one can restrict rather than regulate. If you have one and pressure has dropped, it is worth checking before anything more elaborate.
What happens when you call
Call and describe it
You speak to an engineer, not a call centre. Most jobs can be narrowed down on the phone.
We look at it properly
A real diagnosis before a price, and a straight answer if it is not worth doing.
A written quote
Itemised, so you can see what you are paying for.
The job, and the paperwork
Certificates where the work needs them, and what will need attention next.
Where we do this work
Across Norwich and the whole of Norfolk. If you are on the edge of the county, call and ask — we will tell you honestly whether we are the right people.
- Norwich
- Wymondham
- Dereham
- Attleborough
- Aylsham
- North Walsham
- Cromer
- Diss
- Loddon
- Long Stratton
- Watton
- King's Lynn
Need this doing?
Call and describe the problem — you will speak to an engineer, not a call centre. Written quotes, no estimates over the phone.