Low pressure at one tap is usually that tap. Low pressure everywhere is something upstream of the whole house, and there is a sensible order to work through it.

Most of what follows you can check yourself in twenty minutes, and a fair proportion of the time you will find it without needing anyone.

What a plumber actually checks, and in what order

1. Is it hot only, cold only, or both?

This is the first question because it splits the problem in half. If only the hot is weak, the issue is the cylinder, the combi, or the hot side of the system, not the incoming main. If only the cold is weak, look at the mains supply. If both are weak, it is almost always the incoming supply or the stopcock.

Check a cold tap that comes straight off the main, usually the kitchen sink, before anything else.

2. Is the internal stopcock fully open?

It sounds obvious and it is genuinely one of the most common causes we find. The internal stopcock is usually under the kitchen sink or in a downstairs cupboard.

Turn it anticlockwise until it stops, then back a quarter turn. Stopcocks get partially closed during other work and never opened fully again, and older ones can seize partway.

3. Is the external stopcock open?

There is normally a second stopcock at the boundary, in a small plastic box in the path or pavement outside. It usually needs a long key to reach.

If work has been done on the street, or if the water board has been out, this is worth checking.

4. Is a service valve throttled somewhere?

Isolation valves on individual pipe runs get half closed and forgotten. They are small screwdriver-slot valves on the pipework near appliances, toilets and basins.

If pressure dropped after some other plumbing work was done, this is a strong candidate.

5. Is there a pressure reducing valve or a filter fitted?

Some houses have a pressure reducing valve on the incoming main, and some have a filter or a water softener. Both can restrict flow if the cartridge is blocked or the valve has failed.

Softener bypass valves are a frequent find. Putting the softener into bypass for a minute tells you straight away whether it is the culprit.

6. Are the neighbours affected?

If the whole street is low, it is a supply issue and the water company needs telling rather than a plumber. Worth a knock on a door before booking anyone.

7. Is the incoming main old, narrow or leaking?

Older properties often still have a small-bore lead or galvanised steel incoming main. Galvanised pipe scales up internally over decades and the bore closes in. That gives gradually worsening pressure over years rather than a sudden drop.

A sudden drop with no other explanation, plus a damp patch or a water bill that has jumped, points at a leak on the supply pipe. That needs tracing rather than guessing.

What it usually turns out to be

In our experience the order is: a partially closed stopcock, then a water softener or filter needing attention, then a genuine mains or supply pipe problem. The gradual decline over years is nearly always an old galvanised or undersized incoming main, and the only real fix is a new supply pipe.

When to stop and call someone

Frequently asked questions

Is low water pressure the water company’s problem or mine?

They are responsible up to the boundary stopcock. From there into the house it is yours. Checking whether neighbours are affected tells you which side of that line you are on.

What pressure should I have?

Water companies must supply a minimum static pressure at the boundary, and most properties get comfortably more than that. What matters day to day is flow rate, not just pressure, and flow is what a narrow old supply pipe kills.

Will a pump fix it?

Sometimes, but pumping a supply that is already restricted usually just moves the problem. Find the restriction first.

Why is only my shower weak?

Then it is not a whole-house problem. Look at the shower head for scale, and the thermostatic cartridge.

Need a plumber in Herts, Beds or Cambs?

Vantage Plumbing and Heating covers Hertfordshire, Bedfordshire and Cambridgeshire. The line is answered by a person at any hour of any day, and you get a price before anyone starts. Call 01462 506374 or request a callback.

Related: leak detection · general plumbing repairs · plumbing services.