The majority of boiler breakdown call-outs are due to dirty system water in your heating system.

Dirty water and sludge from scale and rust build-up in the pipework and at the bottom of radiators can cause serious damage. Regularly cleaning your central heating system can help prevent this. With the right knowledge and tools you can undertake a basic cleaning regimen yourself. Alternatively, you may choose to ‘power flush’ your system - a process normally carried out by a central heating/plumbing professional.


Why you should clean your central heating system
  • To make it more efficient
  • To reduce heating bills
  • To improve the system's lifespan
What are the most common signs of sludge and/or rust build-up in your central heating system?

The tell-tale signs of sludge and/or rust build-up in your central heating system are:

  1. The boiler is making more noise than usual
  2. The system takes a long time to warm up
  3. One or more radiators are cold at the bottom or top making some rooms colder than others
  4. Radiators need regular bleeding
  5. Sludge build-up in the feed-and-expansion tank

If you’re experiencing any of the symptoms above, the right time to clean your central heating is now. It is possible to flush a central heating system yourself, continue reading to learn how. Alternatively, you may wish to call a trustworthy plumber to carry out the task.


How to diagnose a system in need of a flush?

The health of a central heating system can be checked with a turbidity tube or an infrared thermometer. Although most households are unlikely to have these items, a plumber may use them to diagnose a system in need of a flush.


DIY: How to flush your radiators

If you're taking the DIY route, one of the simplest ways to clean your system is to remove and flush out each radiator. Accomplishing this task for larger radiators may require two people - or may not be practical at all.


Steps to successfully flush your radiators
  • Make sure the heating system is switched off - or the system may be damaged
  • Lay an old towel/sheet to absorb any drips and leaks
  • Turn off the radiator valve
  • Remove cap from valve in other side of radiator
  • Use adjustable spanner to close valve
  • Open air vent and bleed the radiator a little to dissipate pressure
  • Shut the air vent
  • Slacken nuts on either side of the radiator
  • Then (depending on radiator design) lift radiator and flip it down while still attached to nuts, then detach the radiator in the upside down position - which will minimize spillage.
  • Place fingers over each end and take the radiator outside
  • Tip out water
  • Attach a garden hose to one end of the radiator and turn on mains: this will flush out rust and any other debris.
  • Place the radiator back on the wall: turn on the valves, bleed the radiator


Repeat this process for all radiators.


How to flush the system without removing radiators
  • Switch off the heating system
  • Drain and replace the water in your central heating system; this should remove some sludge
  • For vented system: Add system cleaner to the feed-and-expansion tank (NOT the cold water storage tank)
  • For sealed system: inject special cleaner cartridge into heating system
  • Turn heating system back on and run for two hours - this will distribute the cleaner around the system
  • Drain and fill the entire system at least twice
  • Upon final refill, add a high quality inhibitor to help protect your heating system against corrosion and sludge build-up


What is a power flush it?

It's the process of forcing large volumes of water through a central heating system to clear out rust and other debris which may be reducing the system’s efficacy. Power flushes have different capacities, ranging from a 20 litre tank (enough for 25 radiators) to 200 litre tanks, designed for much larger buildings such as offices or hotels.


Where can I get a power flush?

You can hire a power flush from your local tool hire firm.


How to use a power flush

The precise method of power flushing your system will depend on the machine you use.


Power flush for a gravity-fed, open vented system:

 You'll need:

  • Access and control over the feed-and-expansion tank
  • Ability to drain off dirty water into a foul water drain (or toilet) with a hosepipe
  • Access to heating system drain point/valve
  • Enough hose to connect F&E tank to drain/toilet, and from system drain point to drain/toilet (since these are separate events, you can use the same hose pipe)
  • Central heating system cleaner chemicals
  • Inhibitor


Be sure to lay protective mats around areas where you'll be trailing dirty hoses.


Power flushes are generally connected to central heating systems by two methods:


  • To isolating valves on either side of the central heating pump (the pump must be disconnected)
  • By removing a radiator and connecting the power flush to the radiator tail valves


For most homeowners it is quicker and easier to hire a plumber/central heating specialist with the necessary power flushing equipment and experience. See our guide on how to find a trustworthy plumber here.