Network Pressure Testing: The Pressing That Must Be Done Before Pipes Are Closed

A pressure test is the technical check that confirms whether the water supply network can hold and remain watertight under controlled pressure.

The plumber connects a pump or pressure gauge, fills the network with water or, where appropriate, air, and raises the pressure according to the system method. The reading is then monitored to see whether it stays stable for the required period.

If the reading drops, the cause may be minor or serious, but it is never something to wave away. The point is not that the installation “looks dry”, but that measurement and visual inspection confirm it can hold safely before it disappears behind finishes.

Some of the most common points the test can expose are the following:

If the pressure remains stable and the joints pass a visual inspection, that is a strong indication that the network is watertight under the conditions of the test.

Water lines end up hidden behind walls, floors, tiles, furniture and fixed construction. Once the area is closed, direct access is gone.

If the network is tested while everything is still open, a leak can be found quickly and corrected cleanly. If the same issue appears after finishes are complete, the repair becomes far more expensive, disruptive and time-consuming.

The difference between those two moments is usually dramatic, which is why testing before closure should never be skipped.

The practical difference becomes very clear in the two scenarios below:

Pressure testing should be carried out after the new plumbing work is complete, but before the pipes are covered and access to the critical points is lost.

The same logic applies to the stage of the project when the test should come first:

The correct sequence is straightforward: install the pipework, pressure test it, correct anything that needs attention, repeat the test and only then close the installation.

A pressure test checks whether the network can hold pressure without losses and without hidden weaknesses at its joints.

It does not, however, automatically test the drainage system. Drainage needs its own flow and watertightness check, based on a different logic and different failure points.

In other words, a water pressure test and a drainage test are separate controls and should not be confused.

In a bathroom renovation, one test is not enough. Water supply and drainage are assessed separately because they serve different functions and fail in different ways.

Both tests matter, but they do not measure the same thing and they do not reveal the same failures. In a proper renovation, you check both the pressurized supply network and the gravity-based drainage network.

The breakdown below shows what belongs to each type of test:

If you want a short summary, the core distinction is this:

Every new or modified water line should be tested, not just the main runs that seem most important at first glance.

Pressing is especially valuable in multilayer or PEX systems with press fittings, because it confirms in practice that every joint and every branch was made correctly.

At bathroom or manifold level, that translates in practice into the following points:

Concealed mixers are among the most sensitive points in the network because everything behind the trim becomes difficult to access later.

The mixer body, the hot and cold connections and the outlets to the shower head or handset all end up behind tiles. If a leak is hidden there, the repair usually means opening a finished wall.

That is why a concealed mixer should never be covered until the pressure test and visual inspection of all connections have been completed properly.

Before the wall is closed, the correct procedure can be summed up as follows:

The exact test pressure is not one arbitrary number that suits every project. It depends on:

In many domestic installations, the test is carried out at a pressure above normal operating pressure so that weak points show up before the system is concealed.

The owner does not need to impose a number without knowing the system. What matters is asking the plumber to follow the material specifications, use the correct method and record the outcome clearly.

From the owner’s side, these are the main points worth asking for:

If you want to reduce that to one short question for the plumber, the core point is this:

The duration of the test depends on the system, the method and the manufacturer guidance, so there is no single answer for every installation.

What is clearly not enough is a rushed “we put pressure on for two minutes and everything looked fine”. That kind of shortcut often misses slow drops and weak joints.

In proper practice, the network should stay under pressure long enough to stabilize, allow the joints to be inspected and reveal even a small change in the gauge reading.

1. to raise the pressure,
2. to stabilize the network,
3. to visually check joints,
4. to monitor the pressure gauge,
5. to leave the network under pressure for the required time,
6. to recheck the indication.

Larger projects or more critical installations may require an even stricter process and a longer observation period.

The key point is that the test should not be treated as a box-ticking exercise carried out in a hurry.

In practical terms, that means at least the following:

If the pressure drops, that does not automatically mean a major leak, but it always means something needs to be checked before the work continues.

The plumber should identify the real cause, correct it and repeat the test until the result is stable.

If there is an unexplained pressure drop, the next stages of the renovation should not continue until the issue is resolved.

Modern plumbing systems often use press fittings, especially in multilayer pipework, and they are reliable only when every installation step is carried out correctly.

For them to perform properly, the fitting itself is not enough. You also need the correct press, the correct jaw, proper pipe cutting, proper cleaning and preparation, and a clean pressing operation without an incompatible or defective part anywhere in the chain.

If a fitting is not pressed correctly, it may not fail dramatically on day one. In many cases it shows up later as a small, persistent leak.

Pressure testing is the practical way to catch that kind of mistake before the installation disappears behind finished surfaces.

The test can be carried out with water or with air, depending on the system, the stage of the project and the specified method.

A water test is closer to real operating conditions and usually reveals an obvious leak more directly. The tradeoff is that if something has a major failure, the space may get wet, so more care is needed around finished areas.

An air test is useful when water should not yet enter the network and it can still reveal pressure loss. Because air is compressible, however, the process needs even more discipline and safe handling.

The owner does not need to choose the method personally. The important thing is to insist that the test is done correctly, safely and in line with the system specifications.

The owner does not need to perform the test personally, but it is entirely reasonable to ask for evidence that it was done properly.

That is not a sign of distrust. It is basic technical documentation for a part of the project that will soon be hidden.

If a problem appears later, the photos and record help clarify what was checked and in what condition the network was handed over.

In many cases, plumbers leave the network under pressure during some of the following work so that any new damage becomes visible immediately.

This can be useful because a pipe that was originally sound may be damaged while the chases are being closed or while another trade is working nearby.

It is not always necessary to keep the system pressurized for the entire interval, but a final recheck before permanent closure is good practice.

If the network remains under pressure, the outlets should be properly capped, open points should be made safe and the system should be checked periodically without creating risk for other trades.

If any change is made after the initial test, the network needs to be tested again. The earlier result no longer covers the revised installation.

Every new intervention resets the previous certainty because it introduces a new potential failure point or changes the old result.

“We tested it earlier” is not enough. If something changed, it has to be checked again before it is hidden.

In an installation with a manifold, pressure testing is even more useful because the network is organized into individual lines that can be checked in a targeted way.

The main advantage of a manifold is that the lines are clearer and diagnosis is more organized than in a more scattered pipe layout.

If there is a leak, it is usually easier to isolate the affected line and correct it without unnecessary guesswork.

Pipe insulation is important, but it should not cover joints that have not yet been tested and confirmed.

The correct order of work is:

1. piping,
2. connections,
3. pressure test,
4. correction if necessary,
5. insulation,
6. photographic documentation,
7. closure.

In some projects, part of the insulation may be installed in parallel with the pipework. Even then, the critical points should remain visible and accessible until the test has been completed successfully.

A plumbing quote should not remain vague. Ideally, it should state clearly that a pressure test of the water supply network will be carried out.

A general phrase like “new plumbing” does not automatically mean that a full pressure test with proper documentation is included.

If you want to be covered, ask for it clearly and make sure it is written down.

In a well-organized plumbing job, pressure testing is often treated as part of the normal process and included in the plumber’s scope.

If it is requested as a separate visit or used to assess an existing installation, there may be an additional charge depending on scale and difficulty.

As a broad market indication, the picture is usually as follows:

Even when it is billed separately, the cost of testing is small compared with the cost of repairing hidden leakage behind newly finished surfaces.

Some of the most common mistakes that undermine the value of the test are the following:

Before the network is closed, it is worth getting clear answers to the following:

If the answer is “there is no need”, ask for a technical explanation. In a new water supply installation, this is generally a check that should be carried out.

Use the checklist below to make sure the test covers all the critical points:

If most of the answers on this checklist are “no”, the installation should not be closed yet.

A homeowner is carrying out a full bathroom renovation. The plumber installs new pipework, connects the supply points and fits a concealed shower mixer, but no proper pressure test is performed because “everything looks dry”.

The chases are closed, waterproofing is applied, tiles are laid and the bathroom is handed over without real proof that the hidden network was tested.

Two months later, damp appears on the wall behind the shower and a small leak is eventually traced to a joint on the concealed mixer.

The repair now requires tile removal, local rebuilding and a much higher cost than the original check would have involved.

If a proper pressure test had been carried out before the wall was closed, the issue would most likely have been caught in time.

In another renovation, once the pipework is complete, the plumber caps all supply points and carries out a proper pressure test on the network.

In practice, a proper test covers at least the following points in an organized way:

The network remains under pressure, the gauge is photographed, the joints are visually inspected and no pressure drop appears.

After that, the pipes are insulated, the routes are photographed and only then are the chases closed and the finishing works allowed to continue.

That is the safe, logical procedure that greatly reduces the chance of hiding a problem inside the wall.

Do not allow the water supply lines to be closed without a pressure test.

Pressing is one of the most important checks in a bathroom renovation. It is not enough for a contractor to say “it is not dripping”. The network should be pressurized, monitored and confirmed stable without pressure loss.

Ask for photos of the pipework and the pressure gauge before the walls are closed. If there is a concealed mixer or a manifold, the check becomes even more important.

If anything changes after the first test, ask for the test to be repeated. Every new joint should be checked before it is hidden.

Pressure testing, in other words pressing the network, is an essential step in any serious bathroom plumbing installation.

It confirms that the hot and cold water lines, joints, fittings, supply points, concealed mixers and manifold are watertight before they disappear behind tiles and built elements.

In final summary, these are the main points that should stay in place:

The time and cost involved in pressing are minor compared with the damage caused by a hidden leak behind new finishes.

In a proper bathroom renovation, pipes are not closed because they “look fine”. They are closed only after they have been tested and documented as safe.