How to Find A Leak In Your Central Heating System

Learning how to find a leak in your heating system is an important step to take before calling a heating leak detection specialist. Finding the leak yourself may be possible if the leak is in a visible location. A hidden water leak will require specialist equipment to locate.

This guide provides DIY steps to locate a leak on a central heating system.

  • A boiler leaking water will lose pressure over time.
  • Coloured Paper placed under the boiler may show if the boiler has a leak.
  • Radiators can leak from valves, fittings and corrosion of the radiator
  • Thermostatic Radiator Valves can develop faulty pins leading to leaks
  • Pressure Relief Valves can become faulty causing a leak.
find a leak in a central heating system

Common signs of leaks include:

  • Boiler pressure dropping as the heating system loses water
  • Damp & Water damage to walls, floors or ceilings caused by leaking heating pipes
  • Gurgling sounds from air mixed with water in the heating system
  • Cold radiators with the heating on is a sign of air in the system.
  • Needing to frequently bleed radiators to remove air from the heating circuit.
  • Feed and expansion (F&E) tank filling constantly indicates that the central heating system is losing water.
  • Warm patches on the floors caused by hot water seeping out of pipes into the concrete screed.
  • Condensation, mould or a damp smell with lack of apparent cause.
  • An increase in water bills due to a gravity fed (vented) heating system constantly filling
  • A plumbing or heating engineer has confirmed there is a leak in your heating system.

A hidden water leak will require specialist equipment to locate. As a leak detection specialist we use tracer gases, thermal imaging, and acoustic listening devices to locate hidden leaks on central heating systems and pipework.

Follow these DIY visual inspection steps to locate a leak on a central heating system

Visually Check Under and Around the Boiler

Visually inspect the area under and around your boiler. Look for any signs of dripping or spraying water, unusual wet spots, or corrosion on pipes and connections.

Discoloration, rust, or water marks could indicate a persistent leak from a boiler component.


Place blue paper towel under the boiler to detect leaks

To detect less obvious leaks, place some blue paper towel under your boiler.

Over time, any water marks or drips will become evident on the paper towel, indicating the presence and location of a leak. This simple yet effective technique can be a first step in leak detection before moving on to more sophisticated methods or calling in professionals.

Step 1: Remove the cover from the underside of your boiler (if one is present)

Step 2: Place the blue paper towel under the boiler

Step 3: Leave the heating system switched on for at least 1 hour to fully heat the system

Step 4: Check the paper towel for any water marks from drops of water.

Leave the paper towel under the boiler if there are no signs of leaks after 1 hour, checking for water marks over the following days.


Check Radiators for Leaks

Examine all radiators in your home for any signs of leakage. Pay special attention to the valves and pipe connections, as these are common leak points.

Look for water stains, rust, or peeling paint on the walls or floors surrounding the radiators, as these can indicate a slow leak.

Touch and feel for dampness or a drop in temperature at the bottom of the radiator, which might suggest water is escaping.

  • Check each radiator individually for water leaks
  • Check connectors and valves at the base of the radiator
  • Ensure bleed valves at the top of the radiators are closed
  • Check the base of each radiator for rust or water seepage

Check for Faulty Thermostatic Radiator

Inspect the thermostatic radiator valves (TRVs) for any signs of leakage. TRV’s control the flow of water into each radiator, and if they are faulty or damaged, they can be a source of leaks. Look for water seepage, corrosion, or irregular operation of the valve.

  • Remove the head of the TRV Valve and feel for water around the pin.
  • Check the ground below the TRV for visible signs of water leaking such as drip marks, damp or wet patches.

Check Your Pressure Relief Valve for Leaks

Check the area around the pressure relief valve for signs of water discharge, drips, or consistent moisture. A leaking PRV can indicate an over-pressurized system, which requires immediate attention.

  • Locate the PRV
  • Look for signs of leaks including damp & corrosion

Can I Use a Central Heating Leak Sealer If I Can't Find the Leak?

We do not recommend the use of central heating leak sealer.

Heating sealant will usually stop the leak but can cause damage to your heating system components. Sealant in the heating pipes, radiators and boiler makes professional leak detection techniques less effective.

Call a Professional Leak Detection Company to Find Your Leak Using Tracer-Gas Leak Testing, Thermal Imaging & Acoustic Listening Devices

When DIY methods are exhausted or if the leak is elusive it’s time to call in a professional central heating leak detection company.

Our experts use advanced techniques including tracer-gas leak testing, thermal imaging, and acoustic listening devices to accurately locate even the most hidden leaks.

  • Nitrogen / Hydrogen Tracer Gases are pressurized into the heating system. The Tracer-gas will escape from the location of the leak. The tracer gas is detected above the ground using a specialist gas detector.
  • Thermographic cameras are used to trace the heat source emitted from hot central heating pipes. Temperature differences are easy to identify and can indicate the location of a water leak.
  • Acoustic Microphones are used to listen for the sound of escaping water under the floor or from pipes in walls or ceilings. The hissing sound of escaping water can be detected by acoustic leak detection specialists.