X500 Inhibited AntifreezeProtect

Protection for closed loop hydronic heating systems against limescale, corrosion and freezing temperatures

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

Limescale and corrosion are the two main causes of hydronic 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 Sentinel X500 Inhibited Antifreeze in the system 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 will depend on the level of frost protection required; see the following table. A dosage of 20% v/v (i.e. 5 gallons of Sentinel X500 added to a system having a typical volume of 25 gallons) or more is needed to achieve the minimum concentration of corrosion and scale inhibitor.

For best results, it is recommended that systems are cleaned and flushed using a suitable Sentinel cleaning product. If the system is already noisy due to limescale deposits in the heat exchanger, Sentinel X200 should be added together with Sentinel X500.

Open Systems: Dose via the expansion header tank, via a by-pass feeder or use a dosing bottle.

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

% v/v Sentinel X500 20 25 30 35 40 45 50
Freezing point (°F)
ASTM D1177
22 17 11 5 -2 -11 -20