Head Office Number:

Beginners Guide to Draining a Central Heating System

So, you have a central heating system in your home but have you ever thought about maintaining it to ensure that you extend its life? Your central heating system relies on its performance and sometimes, it does need draining and cleaning. There are many reasons as to why you might do this but did you know that you can do it yourself?

Why is it Important to Drain a Central Heating System

It’s not just maintenance that requires you to drain your system but when you drain it, you will remove the sludge and limescale that builds up within it. In doing this, you will be able to do everything you can to help prolong the life of your boiler while ensuring it remains in good working order. It’s inevitable that at some point you will need a boiler replacement but looking after your boiler is vital.

How Do You Drain a Central Heating System?

Every home will rely on its heating system for heating and hot water. So, how do you drain the system?

1. Begin by switching off the system as this will ensure that all pipework can cool down.

2. If you use solid fuel to run your boiler then you should ensure that the flame has been extinguished before waiting until the boiler becomes cold

3. At this point, you should isolate the water supply. This will prevent further water from entering it while you work. Locate the stop tap in your home and turn it to stop the water from flowing.

At this point, draining methods will differ from combi boilers to conventional boilers. If you are draining a combi boiler then you must switch off the system, allow it to cool down and then follow the draining process.

4. Locate the correct radiator in the home that will be used to drain your system. This is commonly located on the first floor. To identify it, you will see a drain valve located on it. Now it’s time to find yourself a hose and clip it to the outlet, ensuring that the water runs outside. It’s important to remember that the inhibitor contains chemicals so make sure the hosepipe is located away from your lawn or plants.

5. Now it is time to begin bleeding the radiators. So, open the bleed valve, allowing the water to run through the system. If you want to speed up the flow of water, it makes sense to begin with the radiators located on the top floor. After around 15 minutes you can then open the bleed valves in the radiators located downstairs.

It’s common for air to get into the system and that can prevent the water from moving. If this is the case, add around 15cm of water to the tank and loosen the valve. This will then allow the water to begin running out of the hose. If that doesn’t work then you have locked air which means joining the other end of the hose to the cold tap before giving a blast of water back into the radiator that you are draining.

6. It’s time to open the drain valve to discharge the water. All of the radiator valves within the house should be open. Now you should open the radiator valve that the hosepipe is attached to in order to durian your heating down. This process will take anything from 20 minutes to one hour, depending on the system you have. By opening the bleed valves of your radiators, you will speed up the process.

7. Once it has been drained, it’s time to refill the system. To do this, close all valves as well as the drain cock on the radiator. Allow the system to be filled up by connecting the string in the feed tank. With the tank full, begin bleeding the radiators downstairs. You can then repeat this with the upstairs radiators, leaving your system filled.

It is recommended that you add an inhibitor to your system as this can reduce the build-up of limescale and corrosion. Ensure all valves are tightened and then turn on the power. The system will need to heat up but once it is done, you can bleed the radiators again.

Draining a System That Doesn’t Have a Drain Valve

1. Begin by turning off the system and isolating the water supply. Again, allow the pipes and radiators to become completely cold. If you have a combi boiler then turn it off, allow it to cool and discharge the water. If you have a conventional system then isolate the water first and then turn off the boiler.

2. If you’re draining a system that doesn’t have a drain valve you will be required to separate the radiator by the system and close the two valves. Turn the regulator in a clockwise direction. For the lockshield, take off the plastic cap and use pliers to close the valve tightly.

3. It’s time to bleed all of your radiators, so open the valves to allow air to be released from the system as this will make draining the system faster.

4. Now you will need to loosen the union nuts to prevent water from leaking. So, the method you should use to drain a central heating system that does not have a drain valve should look like this:

  • Release the coupling nut located on the regulator side
  • Position a bucket and any rags beneath it, while you should have a towel at hand.
  • Using a spanner, turn to the nut counterclockwise until water begins entering the bucket.

5. Once you have the radiator valve in the off position, you should attach a host and begin to drain the system. The hose will require a special fitting to attach correctly which is either a speed fit tap or a speed fit draining fitting. With the radiator empty, you can remove the radiator should you wish. However, avoid spilling any water as this can stain.


Draining a central heating system is not a difficult process with the correct research and planning. It’s important to follow every step correctly and take your time while you should make sure that you have all the right tools to hand. However, if you are not completely confident and do not feel as though you can do it, you should not attempt it as this could cause damage to your heating system that might lead to the need for a boiler replacement. In this case, it makes sense to speak with a professional heating engineer who can carry out the job with ease, ensuring your system is working effectively.

Our Partners

A-Rated Boiler Installation Made Easy

Answer 8 Simple Questions

And receive an instant online quote, now that's what we call super easy.

Book a Free Boiler Survey and Find the Best A-Rated Boiler

You pick a survey date and time, we give you a variety of A-Rated boilers to choose from.

Choose an Install Date and Time

With A local Gas Safe approved engineer that’s just a stone’s throw away from you.

Get An Instant Quote

Real People, Real Experiences, Real Reviews

Next Day Installation

New Boiler with Installation from only £9.99 a month

Get Your Instant Quote

Simply complete the form to receive your free quotation.

County Form

"*" indicates required fields

This field is for validation purposes and should be left unchanged.
10.9% APR Representative Example: Cash Price £1,800. Deposit Payable £1,056.00. Total Amount of Credit £744.00. Total Interest £455.24. Total Amount Repayable £2,255.24. Repayable by 120 monthly instalments of £9.99. Representative 10.9% APR (fixed). Rate of Interest 10.9% a year (fixed). Duration of Agreement 120 months.
Get An Instant Quote

What's Included With Your A-Rated Boiler

Up-To 12 Year Manufacturer Warranty

24 Month Workmanship Warranty

Magnetic Filter

Limescale Filter

Chemical Flush

Free Hive Thermostat (Worth £300)

Get An Instant Quote

Keeping It Local Since 2010

Since 2010, Prime Time Boilers have been working with and supporting local Gas Safe approved engineers across England. No matter where you are based, we are just a stone through away.

Get An Instant Quote

Get Your Instant Quotation Now

Click Here For Your Instant Quote