Leak detection underfloor heating without breaking up floors

Signs of a leak

• Boiler pressure keeps dropping
• Wet or warm spots in the floor
• One zone stays cold
• Topping up only helps briefly

Related topic: central heating boiler pressure loss.

How we find it

Using thermography, pressure tests and targeted measurements, we determine which circuit is leaking. Then repair as minimally as possible. More methods: 8 leak detection methods. Service page: leak detection.

Where underfloor heating leaks and what you can do yourself

A leak in underfloor heating doesn't always have to be in the floor itself. Often it's in a place you can simply inspect. It helps to rule out the easy spots first before searching in the floor.

Common causes

• The manifold. That's the cabinet where all the underfloor heating pipes come together. Couplings, valves and bleed valves can leak there. This is the first place to check.
• Damage during DIY work. A drill hole for skirting boards, a door stop or a new floor can hit a pipe. If the pressure loss occurs shortly after DIY work, that is an important clue.
• Old pipes. In older systems, pipes can become brittle or joints in the floor can start to leak.
• Other parts of the central heating system. A leaking radiator, a pipe in a crawl space or the boiler's pressure relief valve gives the same symptoms.

What you can safely do yourself

• Open the manifold cabinet and look for drips, limescale marks or rust traces at the couplings. Put dry kitchen paper underneath to see if it gets wet.
• Note the pressure on the boiler every day. This way you can see how quickly it drops, and that helps with the search.
• Also check radiators, the boiler and the crawl space for moisture.
• Only top up the system according to your boiler's manual, and don't keep topping up endlessly. Constantly adding fresh water to the system causes more limescale and rust.
• Never drill or saw into a floor with underfloor heating without knowing where the pipes are.

When to call?

Is the pressure dropping quickly, is there a wet or noticeably warm spot in the floor, or is the boiler shutting down on low pressure? Then call a tradesman. With an active leak, water keeps getting under your floor. That can damage the screed, the floor finish and downstairs neighbours.

What the professional work involves

The technician closes off the groups one by one on the manifold and checks with which group the pressure keeps dropping. This shows which circuit the leak is in. Then a thermal imaging camera makes the course of the pipe visible and shows where the water is spreading. The floor is only opened at that spot. The pipe is repaired with a coupling suitable for underfloor heating, after which the circuit is pressure-tested and bled. Only when everything is sealed is the floor closed again. You can read more about the installation itself at underfloor heating.

Step-by-step plan for pressure loss on the boiler

Pressure loss is often the first signal. With these steps you can map out what's going on, so the technician can search in a targeted way.

1. Read the pressure on the boiler and write down the value and time. Do this for a few days at the same time.
2. Check at the boiler whether water is running from the pressure relief valve or the drain underneath. If it's dripping there, the problem may not be in the floor but at the boiler or expansion vessel.
3. Check the manifold for drips, limescale marks and damp patches, as described earlier on this page.
4. Check the radiators and visible pipes, including in the crawl space or meter cupboard.
5. Watch the floor: a spot that feels warmer than the rest, loose tiles, bulging laminate or a musty smell.
6. Only top up when necessary and according to the manual. Keep a record of how often you top up.
7. Call with your notes to hand. How quickly the pressure drops says a lot about the size of the leak.

Leak, or something else?

Not every pressure loss means a leak in the floor. A few other causes are common.

• A defective expansion vessel. The vessel absorbs the expansion of hot water. If it no longer works properly, the pressure fluctuates strongly and the boiler discharges water via the pressure relief valve. More about this at replacing expansion vessel.
• Air in the system. After topping up or bleeding, the pressure can drop slightly without there being a leak. A zone that does not get warm can also be caused by air.
• A leaking radiator or boiler. That sometimes resembles a floor leak. At central heating boiler or radiator leaking you can read what to look out for.

If the pressure drops even when the heating has been off for a while and the system has cooled down, that points more to an actual leak.

What you'd better not do

• Putting a leak-stop product into the system yourself. This can damage valves, pumps and the boiler and makes later repair more difficult.
• Pulling up tiles or laminate at random to see where the leak is.
• Continuing to top up for months without having the cause investigated. Water under the floor can unnoticed affect the screed and the downstairs neighbours.
• Opening or closing circuits on the manifold if you don't know how your manifold works. At least note how everything was set.

After the repair

After the repair, the circuit is filled, bled and pressure-checked. Keep an eye on the boiler pressure yourself for the first few days; if it remains stable, the leak has been fixed. A screed that has become wet needs time to dry before a new finish can be applied. If in doubt, ask for advice before having a new floor laid.

If you have damage to the floor or at the downstairs neighbours, report it to your insurer. They often ask for a report of the investigation; see leak detection report for insurance and water damage and compensation. If it's actually about the boiler itself, see central heating boiler.