Why Has My Water Pressure Dropped

If the water pressure in your house has dropped, the first job is working out which pressure you mean, because two unrelated things share the name. Mains water pressure is what pushes cold water out of your taps and feeds a combi boiler. Boiler pressure is the small gauge on the front of the boiler, and that belongs to the sealed heating circuit, which has nothing to do with your taps at all. A drop in one tells you nothing whatsoever about the other, and they are put right in completely different ways.

Once that is settled the list of causes gets short quickly. A drop at one tap is nearly always that tap. A drop across the whole house is the supply, a stop tap or a leak. A boiler gauge that keeps sinking means the heating circuit is losing water somewhere, which is a different job again. We are a Gas Safe registered and OFTEC certified plumbing and heating business based in Bearsted, and what follows is how we work through it on a call-out, in the order we would check it.

Which pressure has actually dropped

Run the cold tap at the kitchen sink. That is your mains pressure, and it is what your water supplier delivers to the boundary of the property. Now look at the boiler. Most combis and system boilers carry a gauge reading in bar, typically sitting somewhere around one to one and a half when the system is cold. That gauge is measuring water sealed inside your radiators and pipework and topped up through a filling loop. The two bodies of water never meet.

The distinction matters because the wrong diagnosis costs money. We have found that a good share of the pressure calls we take are people who have been topping up a boiler that was never the problem, or who have been quoted for a mains issue when the only thing that had actually moved was the gauge on the wall.

Pressure and flow are not the same thing

This causes more confusion than any other part of the subject. Pressure is the force behind the water. Flow is how much of it actually arrives per minute. You can have perfectly good pressure and poor flow, and it is flow that decides whether a shower feels strong.

It matters most on a combi, because a combi heats water as it passes through rather than storing it. Restrict the flow and the boiler has less water to work with, so the hot water suffers first while the cold taps still seem fine. A shower that has quietly gone weak while nothing else has changed is usually a flow problem rather than a pressure one, and the restriction is normally close to the outlet.

When it is only one tap or shower

If the rest of the house is unaffected, stop looking at the boiler and the stop tap. The fault is at that outlet, and there are only a few candidates.

• The aerator on the end of the tap. It unscrews by hand or with a cloth, and it is usually full of grit or scale.
• The cartridge inside a mixer tap or a thermostatic shower valve, which seizes or silts up over time.
• The isolation valve on the pipe feeding it, which gets knocked, or never gets fully reopened after previous work.
• The flexible tail on a monobloc tap, which can collapse internally and strangle the flow with nothing at all visible from outside.

In this part of Kent the first two are the usual answer, because limescale is quietly at work on every aerator and cartridge in the house. From working with customers across Maidstone and the Medway towns, an aerator nobody has ever cleaned is one of the most satisfying five minute fixes in the trade.

When the whole house has dropped

A drop everywhere points at the supply, so work outwards from the house.

• The internal stop tap, usually under the kitchen sink. If anyone has had work done recently it may not have been opened fully afterwards.
• The external stop tap, in the pavement or the front garden.
• Any filter, softener or scale reducer on the incoming main. All of them restrict flow once they are due attention.
• A pressure reducing valve, common on newer properties, which can be set too low or fail outright.
• The supply pipe itself. Plenty of older Kent housing still runs on narrow or lead pipework that was adequate for one bathroom and is not for three.
• Your supplier. Planned works, a burst on the network, or a shared supply where a neighbour's demand affects yours.

That last one is worth knowing about if you live in a Victorian terrace in Maidstone or the Medway towns, because several houses drawing off one original main is common here. The giveaway is pressure that sags predictably at breakfast and early evening rather than dropping at random.

A sudden total loss, especially with water appearing where it should not be, is a different situation. That is a burst rather than a diagnosis, and it wants the stop tap turned off and an emergency call-out rather than an afternoon of investigation.

When it is the boiler gauge falling

A sealed heating system should hold its pressure for months on end. If yours does not, water is going somewhere, and one question splits the diagnosis cleanly in half.

In our experience, checking the discharge pipe on the outside wall works better than starting at the radiators when a boiler keeps losing pressure, because a passing relief valve is the most common cause and it leaves its evidence outside where nobody thinks to look.

The question is whether the pressure falls steadily whatever the heating is doing, or whether it climbs high when the system is hot and then sits too low once everything cools down. A steady loss is a leak. That second pattern is almost always an expansion vessel that has lost its charge, and until the relief valve is forced open there is no water being lost at all.

The vessel is one of the things an annual service should be checking, and recharging one is cheap next to what it costs to leave it. Where there genuinely is a leak, the usual places are a radiator valve, the joints on a heated towel rail, the filling loop itself, or pipework running under a floor.

What we find on Kent jobs

A handful of things come up again and again.

• A discharge pipe that has been dripping for months, with a pale stain running down the brickwork beneath it. Nobody ever looks at an outside wall.
• A filling loop left connected and very slightly open after somebody topped the system up, quietly holding the pressure steady and hiding a real leak.
• A softener or filter on the incoming main that has never been serviced, with the water company getting the blame.
• A stop tap closed a quarter turn during a bathroom fit and never opened again afterwards.

The filling loop one deserves a second look, because it hides a problem rather than causing one. The pressure reads normal, so nobody investigates, and the first anyone knows about the leak underneath is a stain spreading across a ceiling.

What to check yourself, and what to leave alone

A fair amount of this is safe to look at. Unscrew and rinse an aerator. Find your internal stop tap and confirm it is fully open. Walk round the outside of the house and look at the discharge pipe coming from the boiler. Check the isolation valve under a basin. Look underneath the boiler for staining or drips.

What not to do is work on the boiler itself. Anything behind the casing is gas work, and gas work belongs to a Gas Safe registered engineer, not as a matter of red tape but because a boiler is a sealed combustion appliance and the consequences of getting it wrong are not a puddle. Repeatedly topping a system up is worth avoiding too, since it masks the fault while steadily making the water quality worse.

Most pressure problems turn out to be small, and the value is in working out which of the three categories you are in before spending anything. One outlet means that outlet. The whole house means the supply. The gauge on the boiler means the heating circuit, and it is telling you water is going somewhere it should not. We cover Maidstone and the rest of Kent from Bearsted, with free home visits and free quotes across Kent. If your pressure has dropped and the obvious checks have not found it, get in touch and we will come and look.