Quick answer
Heating inhibitor helps protect a compatible central heating system from internal corrosion and scale. Test the concentration during routine servicing and re-dose when required by the product instructions or after water loss. Do not assume every system needs another bottle each year.
A compatible radiator dosing funnel can allow treatment through one radiator without draining the entire heating circuit. You still need to isolate and safely depressurise the radiator and make enough room for the measured dose.
Before opening a radiator
Turn the heating off and let it cool. Before removing a complete vent or blanking plug, the radiator must be safely isolated, depressurised and drained enough to make room for the chemical. Releasing a little air is not proof that a radiator is depressurised. Never unscrew a plug on a hot or pressurised radiator. If isolation or draining is uncertain, use a heating engineer.
Using a compatible dosing funnel
- Check that the funnel connection, radiator port and chemical are compatible. Follow the tool instructions for seals and fitting.
- With the radiator cool, safely isolated and depressurised, drain the amount needed for the specified dose and remove the permitted top fitting. Protect the floor and collect discharged water.
- Fit the dosing tool, add the measured dose slowly, then remove the tool and refit the correct vent or blanking plug using its specified seal.
- Check for leaks, restore the valves to their previous settings, bleed where needed and restore the system pressure following the boiler instructions. Circulate the treatment as directed by the chemical manufacturer.
How much inhibitor should you use?
Use the dosage stated for the particular chemical and the system’s water volume. Bottle sizes and concentrations vary; radiator count alone is only an estimate. Do not mix chemicals unless the manufacturers confirm compatibility. A sealed system’s cold filling pressure is set by its boiler instructions, not by a universal value.
Check the concentration, not just the calendar
Test inhibitor concentration as part of routine annual heating-system servicing, using a test suitable for the chemical in your system. Re-dose if the test or the chemical manufacturer’s instructions show that protection is insufficient, and after draining, flushing or water loss where required. Adding another bottle automatically every year can give the wrong concentration.
Follow the chemical, boiler and system manufacturers’ instructions. For background on annual testing, see Fernox’s inhibitor testing guidance.
