Pressure testing underfloor heating: method, readings and records

A pressure test is the only proof you have that the pipe was sound before it disappears under the screed. This guide goes further than the quick test in our step by step install guide: what to isolate, how to read the gauge, how to find a leak, what to do during screeding and in cold weather, and what to write down.

What pressure should I test underfloor heating at?

Test at 6 bar for 60 minutes. That is well above the 1 to 2 bar a sealed heating system normally runs at, so a joint that holds 6 bar will hold in service. MaxHeatUFH recommends 6 bar for 60 minutes, then keeping the system pressurised during screeding.

Don't go above 6 bar. Our auto-balancing manifold is rated to a maximum of 6 bar, so 6 bar is the limit for a test that includes it. Our blending valve pump packs and ball valve sets are rated to 10 bar.

What do I need to pressure test UFH?

You need a hydraulic test pump, a way to seal every open port, and a clean water supply. Everything else is already on the manifold.

• Hydraulic test pump: a manual lever pump with a water tank and gauge. Ours reads 0 to 50 bar and connects with a 1/2" BSP male hose.
• Blanking caps: a 3/4" female blanking cap for every unused outlet. A spare loop has an outlet on both the flow and return bars, so that is 2 caps per spare loop.
• Blanking plugs: a 1" male blanking plug for any open bar end.
• Manifold ball valves: closed during the test, to keep the manifold separate from the heat source.
• Test sheet and phone: to record and photograph the result.

What should I isolate before the test?

Isolate anything not rated for the test pressure. The most important is the heat source: a boiler or heat pump's pressure relief valve is set far lower than 6 bar, typically around 3 bar, and will open or be damaged.

1. Close the manifold's flow and return ball valves, so the test stays inside the manifold and loops.
2. If the pump pack is already fitted, check its rating. Ours are rated to 10 bar.
3. Leave expansion vessels, safety valves and the heat source outside the test section.
4. Cap every unused outlet and bar end.
5. Check the label on each loop matches the room, so you can find a loop fast if the test fails.

How do I pressure test underfloor heating, step by step?

You fill and purge every loop, raise the pressure to 6 bar, let the pipe settle, then hold for 60 minutes and watch the gauge. Use water at room temperature: warm or very cold water changes temperature during the test and moves the gauge.

1. Fill one loop at a time. Open one loop, push water through from the fill valve and out of the drain valve until it runs with no air. Close it and move to the next.
2. Bleed the manifold. Let the air vent clear any air left in the bars.
3. Connect the test pump to a fill or drain valve and open all the loops.
4. Pump up to 6 bar. Go slowly in the last bar so you don't overshoot.
5. Let it settle. Plastic pipe stretches slightly when first pressurised and the gauge may fall back a little. Top up to 6 bar and wait until it holds.
6. Start the 60 minutes. Note the time and pressure.
7. Walk every loop and joint. Check each Eurocone connection with dry tissue, and look along the pipe for kinks or damage where people have walked.
8. Read the gauge at 60 minutes. Photograph it next to something showing the time.
9. Fill in the test sheet and get it signed, ideally by someone who saw the test.

Is a small pressure drop normal?

A small drop in the first minutes is normal while the pipe settles and the water reaches room temperature. A drop that keeps going after you have topped up is not normal, and means a leak or trapped air.

If the pressure is still falling after a second fill and purge, treat it as a leak. Don't screed over a system that hasn't held.

How do I find a leak in underfloor heating pipe?

Most leaks before screeding are at the manifold, so start there, then test loops one at a time to narrow down the rest. A leak in the pipe itself is usually visible damage from a tool, a boot or a sharp edge.

1. Dry every Eurocone connection with tissue and repressurise. A wet tissue shows the joint. Check the insert was pushed fully home and the nut is tight.
2. Check the bar end units, air vent and gauge threads.
3. If the manifold is dry, isolate the loops and test each one on its own. On a manifold with shut-off flow meters, close all but one loop. Otherwise, disconnect loops and cap the outlets.
4. When you find the loop, walk its full length, looking closely at doorways, bends and anywhere materials were stacked.
5. If the pipe is damaged in the floor, replace that loop. Never make a joint in pipe that will be buried in screed.

A pass doesn't prove every metre is perfect. Scored or scratched pipe may hold a short test and weep later, so replace any length you can see is damaged even if the gauge holds. If pressure drops after the floor is finished, see our guide to underfloor heating pressure dropping.

Should the system stay under pressure while screeding?

Yes. Keep the system under pressure while the screed is laid. A barrow wheel, a screed pump hose or a dropped tool can damage the pipe during the pour, and a pressurised system shows that damage on the gauge immediately, while you can still dig back and replace the loop.

• Ask one person to watch the gauge during the pour.
• Agree with the screed team that they stop if the pressure falls.
• Lay boards over the pipe where barrows run, and keep pipe fixings secure so liquid screed doesn't lift the pipe.

Can I pressure test underfloor heating with air?

Use water. Water is the standard test medium for UFH, and some pipe makers do not allow air testing of their products at all. Compressed air also stores far more energy than water, so a failing joint is more dangerous.

If the building could freeze before it is heated, don't leave plain water in the pipe. Drain the system after testing and screeding, or fill it with a nitrite-free glycol antifreeze dosed to the maker's instructions. Ice in pipe that is held by screed can strain the pipe.

What should I record after a pressure test?

Record enough that someone else could check the test later. Pipe and screed warranties often ask for a signed test sheet, and it protects you if a leak is blamed on the install.

Keep the test sheet with the gauge photos and the loop plan. Your commissioning record follows on from it. See commissioning and first heat-up.

Products for this job

• Hydraulic pressure test pump, 0 to 50 bar: £114
• 3/4" female blanking cap: £1.83 each, 2 per spare loop
• 1" male manifold blanking plug: £2.21
• Manifold pressure gauge end unit: £16
• Manifold ball valve set 1": from £22 a pair
• Eurocone connector cores 3/4": £1.42 each for 16 x 2.0mm

Prices inc VAT, October 2026. Browse manifolds and components and tools and fixings.

Frequently asked questions

What pressure should underfloor heating be tested to?

Test at 6 bar for 60 minutes with water, before screeding. Don't exceed 6 bar if the test includes a manifold rated to 6 bar.

How long should an underfloor heating pressure test last?

60 minutes at 6 bar, after the pipe has settled. Then keep the system under pressure while the screed is laid.

Why has my pressure test dropped slightly?

A small drop in the first minutes is usually the plastic pipe stretching or the water temperature settling. Top up to 6 bar and restart. If it keeps falling, look for a leak.

Do I need to pressure test before screeding?

Yes. Once the screed is down, a leak means breaking out the floor. Test before the pour and keep the pressure on during it.

Can I test with the boiler connected?

No. Close the manifold ball valves so the boiler or heat pump is outside the test. Its relief valve opens far below 6 bar.

What pressure should I leave in the system after screeding?

Once screeding is finished, bring the system down to normal working pressure, or drain it if the building could freeze. The final fill is set at commissioning to suit the heat source.

How do I test a loop I add later?

Connect the new loop, isolate the manifold from the heat source, and test the whole manifold at 6 bar for 60 minutes in the same way before the new loop is covered.

Sources: Polypipe pressure testing guidance, Timoleon UFH installation guide, IMI Hydronic UFH commissioning instructions