Why carry out a pressure test before closing in or commissioning
Distinguishing between a pressure test, a test under pressure, and a tightness test depending on the context
A pressure test is used to validate a section before closing in or lagging, when any rework would be costly. A test under pressure means keeping the system pressurized during a construction phase (underfloor heating, standby pipework) to detect impact damage or a loosened joint. A tightness test is the term to use as soon as a formalized protocol is required by a standard or reference document (gas, buried networks, inspection requirements). In all cases, take the pressure and duration values from the DTU, standard, or specification, not from memory.
Your burden of proof in the event of a claim: traceability, photos, and test report
In a dispute, what counts is written evidence. Without a dated and signed test report, the test does not exist. Add time-stamped photos (blanking-off, pressure gauge, sensitive points) and attach them to the site file.
- Site identifier, section, test fluid.
- Starting and ending pressure, duration, ambient temperature.
- Measuring equipment used and responsible person.
When to bring in a high-pressure testing service (sensitive site, difficult access, tight deadlines)
Use a dedicated service on a sensitive site or when the test requires specific equipment (large volumes, buried networks, access constraints, simultaneous operations). You save time and secure the report with a controlled procedure, which is useful with the clerk of works, the project manager, and the insurer.
Common method for a reliable pressure test on pipework
Preparing the network: prior flushing, visual inspection, and isolating the sections to be tested
Before any pressure test, carry out a prior flush to remove flux, sludge, and foreign bodies that could block a component or damage a sealing seat. Perform a full visual inspection. Check press fittings, welds, clamps, expansion points, and blanking-off. Isolate the section under test. Disable sensitive equipment and install blanking devices suited to the test pressures.
Purging air without compromise: why air distorts a water pressure test and how to remove it
With water, air remains compressible. An air pocket compresses during the test, and you read a pressure drop that does not necessarily correspond to a leak. Fill from the lowest point. Open all high points, air vents, and branches until the flow is steady and bubble-free. On complex networks, purge section by section, and note the ambient temperature, which affects the measured pressure. To avoid recurring issues linked to air pockets, installing an automatic air vent may be appropriate depending on the network layout.
Pressurize progressively: gauge with sufficient resolution, stabilization period, then measurement period
Increase pressure in stages using a test pump. Use a pressure gauge with a resolution appropriate to the test, positioned so it can be read during measurements. Allow a stabilization period, then carry out a measurement period over the duration defined by the applicable standard. Record the time, pressure, and temperature in a dated and signed test report. Without a written record, the test carries no weight in a dispute.
Interpreting a pressure test correctly: pressure, temperature, and time
Essential readings: pressure, ambient temperature, time, and site conditions
| Reading | Unit | Where to record it |
|---|---|---|
| Test pressure | bar | Report + gauge photo |
| Ambient temperature | °C | Report |
| Start, stabilization, end time | hh:mm | Report |
Before any pressure test, note the condition of the network (flushing completed, full air purge, high points vented, components isolated, plugs fitted). A changing room temperature, or a manifold that is still warm, is enough to distort the reading.
Understanding a pressure drop: cooling of the test water versus a real leak (quick diagnosis)
If pressure drops while ambient temperature also falls, begin with a thermal stabilization period. Record pressure and temperature at fixed intervals. Once temperature has stabilized, a pressure that continues to fall points to a leak. A pressure that stabilizes points to simple cooling of the test fluid.
Writing an admissible test report: date, signature, reference document, values, and equipment used
An admissible report is dated, signed, and links the test to a reference document (DTU, standard, gas decree). It records the test fluid, the stages, the values (P and T), the pressure gauge identification (range, resolution, calibration if available), and the site conditions. Without a report, the test carries no weight in a dispute.
Pressure testing domestic water systems: cold water, hot water, circulation loop
Choosing the correct reference document (DTU / standards) and copying the pressure and duration values exactly, not from memory
For a pressure test on CW, DHW, and the circulation loop, start from the document that covers your package. In practice, this is often NF DTU 60.1 and NF EN 806-4. Copy the test pressure, duration, tolerance, and method of reading. Transfer them exactly into the dated and signed test report.
Test fluid and points of attention: water, temperature, purging, check valves, and valves
Carry out the test with water after flushing. Perform a full purge at the high points, otherwise air will dampen the pressure and distort the reading. Pressurize in stages with a readable gauge. Note the pressure and ambient temperature. Isolate or bypass anything not intended for the test. Check check valves, pressure reducers, mixers, safety groups, and shut-off devices.
Practical cases: test before partitioning, test after pressing, test after adding equipment
- Before partitioning. Full-system test. Complete visual inspection. Photos of sensitive areas and identification of joints.
- After pressing. Localized test, then full test after the network has been reconnected.
- After adding equipment. Retest the modified section and associated components, with new traceability.
Pressure testing heating, gas, and buried networks: separate tests
Heating pipework pressure test: water, component protection, and test method before commissioning
A heating pressure test is carried out with water, after flushing and full purging. Protect sensitive components, expansion vessel, safety valve, circulator, heat exchanger, by isolating them if required by the manufacturer. Increase pressure in stages with a readable gauge, allow a stabilization period, then measure pressure and ambient temperature. The pressure and duration values must be taken from the DTU and the manufacturer’s instructions, not from memory.
Carrying out a high-pressure tightness test on a gas network: reference document, safety, test fluid, and specific report
Gas is treated separately. The test is carried out in accordance with the applicable gas reference document, with appliances taken out of service and the area secured. The test fluid is generally an inert gas or air, never oxygen. Require a dedicated report with pressure, duration, temperature, calibration, and section identification.
Buried networks: access constraints, leak detection, and backfilling conditions after pressure testing
For buried systems, the key issue is accessibility. Carry out the test before backfilling, with protected measuring points and identified joints. If pressure drops, cross-check with temperature and targeted leak tracing, tracer, listening, tracer gas depending on the network. Backfilling is only allowed after a compliant result and signed traceability.
