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How to Add Water to a Hot Water Heating System in 5 Steps?

Fact checked by Stephen Conklin

how to add water to a hot water heating system

The key to the longevity of any appliance or anything, in general, is maintenance. This goes the same for your central heating system, which is especially essential for colder states or countries. And, one of the vital maintenance processes is to add water to a hydronic heating system.

In this article, we will teach you how to add water to a hot water heating system in order for your heating system to function smoothly. Step by step, we will guide you through the process with tips and tricks to help you on the way. Sounds lovely? Read on!

Table of Contents

Things You Need for This Tutorial


  • Screwdriver – You will be using it to loosen the screws to your water heating system. Specific screws call for a particular size of screwdrivers, so it’s essential to know the screw size you will need for your boiler system.
  • If you have no screwdrivers at home, use a coin, a butter knife, or even pliers that fit your screw should do the work.
  • Needle-nose pliers – The second thing you will be needing is a pair of needle-nose pliers, which could also be an alternative to a screwdriver.
  • The needle-nose pliers have textured teeth that are usually used in crafting and other lighter tasks and are not strong enough to be used to cut hard wires.
  • Using the standard six-inch snout needle-nose pliers for this tutorial is okay.
  • Hosepipe –The hosepipe should be used to let out the dirty water your radiators have collected over time. It should be long enough to run down the drain or into a pail.
  • Washcloth – To keep everything tidy and clean in event of accidental leaking, a washcloth within reach will come in handy.
  • Radiator Bleed Key – Many of us misplaced the radiator bleed key a long time ago, especially if your water heating system is already five or many years older.

Using a screwdriver as an alternative for your lost key will work just as flawlessly.

Steps to Adding Water to a Hot Water Heating System


So now that you have your hot water heating system and all the tools you need in front of you, it’s time to add water to your hot water heating system.

Step 1: Switch off your central heating system

Switching off the heating system will include turning off the main water supply. This step is essential to avoid accidents and stop the flow of water from refilling your water heating system.

Step 2: Draining out the old water

You will need the hose for this step. Take your hose pipe and securely fasten the end to the drain-off valve. Be sure that your hosepipe is long enough to drain into a container or a drain because it will empty dirty water from your water heating system.

Take your screwdriver with you and unscrew the bleed valve and watch as the water starts to flow out of your heating system. This step will usually do it on its own, so it is wise to leave at least ten to fifteen minutes for all the water to drain out of the system.

Protip: Since draining the water will take a minute or so; you can take the time to flush out your radiators. Radiator sludge can build up, and running water will flush the buildup right up.

Step 3: Secure every valve

This is the stage where we add water to the radiator heating system. You do exactly that by ensuring that every valve opening is securely closed and sealed shut. Simply switch on the main water supply when all is done, and water will flow back to refill your tank again.

Protip: To slow down the internal disintegration of your water heating system, treat your tank with a chemical solution or add a magnetic filter. These remedies will slow down the process of magnetite or sludge buildup consisting of rusted metal from your heating system’s pipe and internal structure but will not completely eliminate it.

Step 4: Making sure that radiator is free from air

The next step is bleeding your radiators to ensure that no air is trapped in your water system because air caught in the system will slow the water pressure, which will result in your water movement being constricted and the boiler is unable to heat properly.

In places with extremely cold weather conditions, air stuck in the water system can even result in freezing waters. Do it on every floor where a radiator is found, and keeping a handy washcloth with you will help with the spillage.

Protip: repeating this step at least two times will assure you that no air is left on your water heating system.

Step 5: Double-checking your superb work

Check if your water heating system has been filled to the brim, and once it is, turn your water heating system back on. Things to check off your mental checklist are if it is running smoothly, whether or not the radiators are heating up and if the valves are tightly secured by using your needle-nose pliers to prevent future leaking.

Bonus: Here is a helpful video on adding water to the boiler system.


Presenting you with this step-by-step guide is the result of countless research and dialogue with experts who are more than happy to answer our questions.

We are now presenting them as a foolproof way to add water to your water heating system, and we hope that it will help you as much as it helped us with our heating systems.

Good luck following this guide on how to add water to a hot water heating system, and we would be more than delighted to know what worked and what didn’t for you.

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