Leave-in protection against freezing temperatures, corrosion and limescale

Ideal for properties vulnerable to sub-zero temperatures, Sentinel X500 Inhibited Antifreeze provides protection against limescale, corrosion and freezing. It protects all system metals against corrosion using the same unique blend of inhibitors as Sentinel X100 Inhibitor, but has the added benefit of protecting system water against freezing when temperatures are low. 

Key features

  • Prevents system water from freezing
  • Enhanced limescale and corrosion protection
  • Protects all system metals against corrosion
  • Ensures optimum boiler efficiency
  • Prevents boiler noise
  • Prevents pin-holing
  • Helps prevent the formation of hydrogen gas

Available sizes

5L liquid X500L-4X5L-GB
20L liquid X500-20L-EXP

Limescale and corrosion are the two main causes of central heating inefficiency, leading to radiator cold spots, boiler inefficiency, a noisy system and a multitude of other problems. Once a system has been prepared using one of the cleaners from the Sentinel cleaning range, it should be protected with a Sentinel inhibitor to prevent the occurrence of limescale build up or corrosion.

For properties which are vulnerable to low or sub-zero temperatures, or perhaps are uninhabited during the winter months, it makes sense to use an inhibitor with central heating antifreeze such as Sentinel X500, rather than the traditional Sentinel X100 Inhibitor. Using the same unique blend of heavy-duty specialist corrosion inhibitors, Sentinel X500 Inhibited Antifreeze protects all system metals against corrosion, but provides the added protection against low temperatures.


The dosage of Sentinel X500 inhibited antifreeze will depend on the level of frost protection required. 20L of Sentinel X500 antifreeze added to a typical domestic system up to 10 radiators will provide the minimum concentration of corrosion and scale inhibitor and also protection from freezing down to approximately -6°C. 40L will provide protection to -20°C.

Open Systems: Dose via F&E cistern, via a by-pass feeder or use a Sentinel Dosing Vessel.

Sealed Systems: If the system is empty, add to any convenient point before filling. If full, use a Sentinel Dosing Vessel to inject via the filling loop or other access point.

% X500


Freezing Point (°C)