Pressure and flow are different things, and confusing them leads to buying the wrong fix. Pressure is the force behind the water; flow is how many litres per minute actually arrive. A property can have decent pressure and poor flow if the incoming pipe is narrow, partially closed or furred, and no pump will fix a genuinely restricted supply.
The tests below are quick and tell you which conversation to have.
Test flow before assuming pressure
- Time how long a measured container takes to fill from the kitchen cold tap — that gives litres per minute.
- Compare hot and cold at the same outlet; a difference points at the hot side, not the mains.
- Compare upstairs and downstairs; a big gap suggests gravity-fed hot water rather than a mains fault.
- Check whether one outlet is bad or all of them — a single bad tap is usually a blocked aerator or a partly closed isolation valve.
Common causes on older rural and stone-built properties
Older properties often still have narrow-bore incoming supply, part-closed internal stopcocks that have never been opened fully since a repair, or long runs of small-diameter pipe added piecemeal over decades. Any one of them caps flow no matter what the mains is capable of at the boundary.
Properties on private supplies or with a shared connection have their own considerations, and those need checking before any internal work is priced.
Which fix matches which cause
- Part-closed or seized stopcock: replace with a full-bore valve — the cheapest meaningful win.
- Undersized incoming main: upgrade the supply pipe from the boundary where practical.
- Gravity-fed hot water with a low tank: an unvented cylinder or accumulator gives mains-pressure hot water throughout.
- Good mains but poor hot flow only: scaled plate exchanger or a restricted cylinder coil.
- Genuinely low mains at the boundary: an accumulator or a pumped solution, correctly sized and legal.
Where pumps are and are not allowed
Boosting directly off the incoming main is not simply a case of fitting a pump — there are regulatory limits on drawing from the mains, and an unmanaged pump can affect neighbouring supplies. Where boosting is right, it is normally done with a break tank and pump set, or with an accumulator that stores mains-pressure water for peak demand.
Frequently asked questions
- Will a bigger shower head fix weak flow?
- Rarely. A larger head spreads the same litres per minute over more area and usually feels worse. Fix the flow first, then choose the head.
- Why is only the hot water weak?
- That points to the hot side: a gravity-fed cylinder with limited head, a scaled combi exchanger, or a restricted coil. The cold supply being fine effectively rules out the incoming main.
- Is an unvented cylinder the answer?
- It is an excellent answer when the incoming mains flow is genuinely good and the problem is a low-pressure gravity system. It is the wrong answer if the incoming supply itself is restricted — that needs solving first.
- Can you test the incoming supply before quoting?
- Yes, and we would rather do that than sell a solution that the supply cannot support. Flow and static pressure readings take minutes and decide the whole approach.
Get the flow measured before buying a fix
Tell us your property type and whether the problem is hot, cold or both — that decides which test matters.