Signs of a Blocked Central Heating System (and how to fix it)

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Are your radiators failing to heat up properly? If your radiators are heating up unevenly, with a warm top and a cold bottom, or if it takes a long time for every radiator on your central heating circuit to heat up, it could be a sign of a blocked central heating system.

There isn’t an instant radiator unblocker to help rid you of this problem, but in a few easy(ish) steps, you could solve the problem of your blocked central heating system and save yourself the hassle of booking a gas engineer or carrying out a power flush.

When we talk about a blocked central heating system, what we usually mean is the build-up of rust and sludge in the central heating pipework. This sludge can make it extremely difficult for the heated water to move freely through the system, hence leaving you with radiators that heat up poorly, or in extremely bad cases, not at all. It’s imperative to regularly maintain your central heating system and ensure the pipework is clean, to help prevent any bad blockages, and the spectre of expensive corrective work in the long-run.

Here’s How to Remove Sludge from your Central Heating System:

Most people will be able to manually flush sludge from their central heating system: all you will need is some old towels or sheets to protect your floors and carpets, and also have a mop and bucket handy, ready to mop up any spills. You will also need two wrenches with adjustable heads, a radiator key, plumbers tape, and a bowl. This can be a messy job, but carrying out the following steps will hopefully ensure your central heating is unblocked without the need to call out a plumber.

Firstly, you’ll need to remove the affected radiator(s) in order to clean them. Do this by:

  • Turn the central heating off and wait for it to cool completely down. This is very important, as you don’t want scalding hot water coming from the pipes.
  • Place the towels and sheets underneath the radiator(s), concentrating on the areas where the pipes come through the floor, and around the valves.
  • Isolate your radiator(s) from the central heating system by turning off the valves. Start with the Thermostatic Radiator Valve. Fully turn it to its ‘off position’. You will then need to turn off the Lockshield Valve: This is normally the one with the plastic cover on it. Remove the cover and turn the valve fully clockwise using one of the adjustable wrenches. Make a note of how many turns it took because you’ll need to reset the valve by the same amount of turns when you replace the radiator.
  • Place a bucket under the thermostatic valve and use both the adjustable wrenches to loosen it.
  • It’s now time to loosen the bleed valve using the radiator key: Ensure that the bowl is still under the thermostatic valve while you do this as all of the water will come flowing from the thermostatic valve once the bleed valve is loosened.
  • Use the radiator key to loosen the lockshield valve and then tilt the radiator to get rid of any excess water.
  • Use the radiator key to close the bleed valve.
  • Remove the radiator from the wall.
  • Take the radiator to an outside space to clean, using a hose to flush any dirt and residue through manually.

If the Manual Flush doesn’t work:

If the manual flush is unsuccessful, or if you keep having problems with dirt and sludge build-up, you may need a qualified plumber to carry out a system power flush or drain down. Always employ the services of a plumber who is RGII registered, which means they are qualified to work safely with gas boilers and central heating systems.