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Your Heat > Boiler Installations  > Draining Down Your Worcester Bosch Boiler: A Step-by-Step Guide
Worcester Bosch boilers Sittingbourne drain down a central heating system combi boiler

Draining Down Your Worcester Bosch Boiler: A Step-by-Step Guide

Hi, thanks for tuning in.  In this blog we help you with the old age issue of how drain down a central heating system combi boiler.


Combi boilers provide households with hot water. But their functionality goes beyond this. Hot water circulates through the pipes and radiators in your household and keeps it warm. If you own a Worcester Bosch boiler or any other combi boiler, you should know it’s a good idea to drain the water out of the system from time to time, at least if you want to ensure the top performance of your boiler.

Here we explain how to drain down your boiler in a step-by-step guide and answer some related questions on this matter. It’s our duty to say it would be best to have a Gas Safe engineer do this task for you, but if you want to do it yourself, let’s get started.

Why Draining Your Boiler Is So Important

Although Worcester Bosch boilers are top of the list of best boilers out there, you still want to look after yours. Here are the 3 main reasons why you should drain your boiler:

1. You will reduce the risk of pipes freezing.

Let’s say you are passionate about skiing. That means you will be away for at least 2 weeks in the winter months, possibly even longer. In this case, your boiler is going to be turned off for 2 or more weeks as well. If you don’t want your pipes to freeze, drain that boiler on time.

2. Not draining your boiler can increase the risk of water leaks when changing pipework or having your property renovated.

If you want to remove those rusty and unsightly radiators or change pipework, not draining your boiler beforehand can result in a massive flood and damage your walls and floor.

3. It protects you from paying for expensive boiler repairs or boiler replacement.

Sludge build-up can cause your boiler to fail over time. Draining it eliminates the sludge from the system and keeps your boiler in good condition.

When to Drain Your Boiler?

Release some air from one of the radiators. Is the water coming out clear or coloured? If it has turned brownish, you should drain the boiler asap.

The Simplest Guide on Draining Your Worcester Bosch Boiler

  1. Unplug your boiler from the mains.
  2. Wait for 3 to 4 hours for the water to cool down completely.
  3. Turn off the water intake valve.
  4. Locate the lowest radiator in your home, then try to find the drainage valve, situated on the lowest point of the radiator.
  5. Make sure a hose to the draining valve is well secured so the water exits your home safely.
  6. Open the valves on top of each radiator in your home (bleed valves) and wait until there is no more water coming out.
  7. Close the bleeding valves and the drainage valve.
  8. Locate a braided filling loop underneath your boiler and open it. Let the system repressurise itself to approximately 1 bar. Put the filling loop back in its place.
  9. Check for any leaks around the boiler or radiators. If there are none – congratulations, you’ve drained down your boiler and extended its life.


We know we’ve made draining down your boiler as simple as pie, but there are several things that could go wrong if you want to do this yourself. If your boiler is still under warranty, why wouldn’t you have a professional drain it down for you? On the other hand, if its warranty has expired and there are multiple failures within the system, getting a replacement boiler would be the best idea. We supply and install Worcester Bosch boilers. Get an instant quote or contact us for more information!


We hope this helped with how to drain down a central heating system combi boiler

Your Heat
  • Mike
    August 21, 2023 at 4:57 pm

    Hi. I was hoping I could pick your brains. I need to replace a bathroom rad, and later, add fresh inhibitor, so have decided to drain down my system, but as I have no drain-down cocks coming off of any of my rad valves, I have decided to use one of the two drain cocks in my WB 25/32 Greenstar oil fired boiler. The problem is which one. I’m pretty sure it’s the one on the bottom left side at the front of the boiler, but I have just noticed one on the bottom right as well. My manual says the one on the left is the drain for the Heatslave tank, and the one on the right is for the primary heat exchanger. I was definitely going to use the former, but after just having noticed the latter, it has thrown me into a slight state of doubt.
    Hoping you can help.

    • Tom Hewitt
      January 3, 2024 at 2:59 pm

      Mike, sorry, i think we missed this, feel free to call 01732 622990 and ask for Tom

  • Mesut Yaman
    December 3, 2023 at 8:59 pm

    Thank you very much for the full explanation of the drain from a heating system .
    But I only needed to see the drain point of Worchester Bosch 8000 Style 35 Kw. That I can drain the boiler only to pressure the expansion vessel. Because the system was already drained two weeks ago while fitting the new Bosch by the Antlin plumber in Swansea was a horrible dirty job .because the blue pressure valve not working I can hear some usual noise but not filling water I suspect their dirty job maybe the valve has been blocked.
    My brand new boiler cost me 3,500 but This is the second week it stopped working .

    My 35-year-old Potterton Flamingo never stopped and gave me any trouble in 35 years. No need to adjust the pressure or any other problem. 3,5 000 spent for the Worchester Bosch 8000 Style I am keeping myself with the gas cooker heating last two days.
    40 years ago I had the Early Valliat was the best central heater ever 4 years I used it without any trouble until I sold the house and moved to Wales and started using Potterton with no problem
    Kindest regards
    Mesut Yaman

    • Tom Hewitt
      January 3, 2024 at 2:57 pm

      Hi Mesut,

      Sadly there are some installers out there that dn’t see the impportance of a clean system.. New boilers really do need a clean system to operate efficiently and effectively, not to mention reliably. Perhaps speak with Worcester about a visit to make sure they’re happy with the installation and they may ask the engineers back to rectify anything they’re not happy with

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