How to add inhibitor to combi boiler?

Combination boiler or combi boilers are the most commonly type of boilers which are used in UK for a reason. Unlike the system and conventional boilers which requires a hot storage cylinder, the combination cylinder is an all in one unit which produces hot water for taps and central heating. Also it saves a great space in your homes and its installation is easy and faster comparative to any other boiler.

It usually takes the water from the main supply and results in stronger water pressure. It provides you plenty of hot water. Thus, no longer waits for the tank to refill again and again.

Modern high efficiency unit boilers are the stainless steel condensing boilers with its built-in heat exchanger to provide hot water to a home or a building. During the cold season, combi boiler runs when needed to heat the structure and provide hot water to various hot appliances. Whereas in hot summer days, combi boiler works whenever there is a need for domestic hot water.

There are two main reasons behind the combi boilers great and powerful efficiency i.e. these units have high operating efficiency and low internal water volume. This means when in summer days you don’t need space heating you are only paying to heat hot water which is domestically required.

Types of combi boilers

Gas combi boilers – Natural gas combi boilers are commonly used by the residents of UK. Also if your homes are connected with the gas network than this is the best choice for you in terms of keeping running costs down.

Oil combi boilers – For the homes not connected with the gas networks, oil boilers is a good option. These boilers need an oil tank to be kept outside your home and once the oil is on the edge you need to top it up from the suppliers.

LPG combi boilers – LPG stands for Liquefied Petroleum Gas made with the combination of gaseous hydrocarbons. They are almost same as oil boilers as they also need a tank which is needed to refill once the gas is about to end.

Electric combi boilers – An electric combi boiler is slightly different from all the other combi boilers as they don’t require any tank or gas network. The water passes over an electric element in the hot cylinder which has an immersion heater. This is popular where the homes are not connected to the gas network or oil is too expensive to buy.

What is an inhibitor?

A central heating inhibitor is a liquid made up of various chemicals that are unpleasant to our skin but very favorable to our central heating system.

What is the importance of an inhibitor?

Inhibitor has become a necessity as the construction of expensive heat exchangers in aluminum becomes the standard boilers in the market.  Inhibitor keeps the system run for longer period of time with the better performance and keeping your family warm and cozy in the winters.

Now after knowing so much about the inhibitor, you might be thinking how to add inhibitor to combi boiler? Don’t worry we have the answer to this question. So, keep reading!!

You can add the inhibitor in 3 different ways.

You need to drain the system to add the inhibitor

  • Drain or unit and add the normal inhibitor to it
  • You can pour it by removing a plug on the top of the towel radiator
  • You can inject it into the radiator with washing liquid bottle after removing the air vent plug.

Injecting through the bleed valve without any draining of the system

  • Allow the radiator cool down after switching off the system
  • Try to select the radiator without the thermostat radiator valve.
  • Now shut both the radiator valves and remove the blood screw
  • Attach the inhibitor cartridge to the radiator.
  • Inject the concentrated valves while opening the radiators.
  • Now shut the radiator valves and remove the radiator cartridge calmly.
  • After this you need to refit blood screw and open the radiator valves
  • Run your system for 15 minutes to disperse the inhibitor around the system.
  • After this process, you may need to bleed the radiator.

Injecting through the filling loop, without draining the system

  • Switch off the system and allow the radiators to cool down.
  • Now turn off the tap and remove the filling loop
  • Join the inhibitor cartridge with the adapter
  • Turn on the tap and inject the inhibitor concentrate
  • Turn off the tap and remove the adapter
  • Now refit the filling loop
  • And allow the system to run for good 15 minutes to disperse the inhibitor around the system.


These steps will surely help you to understand how to add inhibitor to combi boiler? But don’t forget all these steps have to be done carefully and if you notice any fault with the system or the inhibitor, call the engineer immediately.

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