Power Flushing heating systems

Power Flushing Central Heating Systems  


Keeping the water in the central heating system clean dramatically reduces the chances of break down and helps reduce energy bills Power flushing cleans the central heating system by forcing cleaning agents and high pressure water through it. Power flushing removes debris build up and rust and may be the solution to cold spots or radiators being warm at the top and cold at the bottom. Failure of one radiator on its own is not a reliable sign that power flushing of the whole system is necessary although it might be. If problems are confined to one radiator it’s advisable to contact a professional. Hiring a machine for power flushing one radiator let alone the whole system might turn out to be a waste of money and not solve the problem. Sludge in the expansion tank and in the ‘feed’ or a heating system slow to warm up might be a sure sign that power flushing is due. Further signs that the system might benefit from power flushing can be thermostatic valves stuck in the off position. If this is affecting more than one radiator power flushing might be unavoidable. The most reliable first indicator that power flushing is required is to see whether any problems are affecting more than one radiator. Some on line companies offer a service where you send them a sample of your central heating water and they test it to tell if your system need power flushing. Seriously blocked systems require power flushing, where an abrasive powder is passed through the system instead of water.

Power Flushing Units


Power flushing machines come in a number of tank sizes. Most are between 20 litre which is enough for as many as 25 radiators right up to 200 litre tanks which will perform power flushing on large commercial premises. Even larger power flushing machines are available for large industrial concerns. Some machines have reversible power flushing pumps which make it easier to dislodge the debris.  Power flushing machines can be hired readily. Some cheaper power flushing machines however will limit you to connecting to one radiator at a time. Power flushing the whole system at once is a better option if your system really needs any flushing at all. Even domestic power flushing machines have a flow rate of around 100 litres a minute. That’s enough to fill a bath in less than a minute so take precautions. Always ensure you have a power flushing machine which is up to the task. It’s far better to hire a good machine than to buy a cheap one. But if you do consider buying a power flushing machine check for a good second hand one before committing yourself to something new. It is actually possible to build your own power flushing machine for as little as £300 but it’s not something we’d recommend for occasional flushing in your own home.

You need to check what type of central system you have. ‘Sealed systems’ have a pressure gauge and ‘open vented systems’ have a tank in the loft. This article is intended only for power flushing open vented systems. Advice on power flushing sealed systems which will be available separately. At this stage consider whether it’s best to call a professional. No great plumbing skills are required to carry out straightforward power flushing but it’s advisable to have sufficient skill to disconnect a radiator. If there are any problems with the system contact a professional. Some insurers require proof of power flushing in the form of a power flush certificate. If you need such a certificate you might have no choice but to have the work done professionally. You may also consider that if you have an old slightly fragile system power flushing may cause some damage. This is not that common but it can happen. Indeed if power flushing is done properly and some minor damage does occur it might be considered a blessing because it will have identified a failing in the system that was there anyway.

Power flushing involves chemicals. Never use acid. It’s advisable to buy three chemicals. ‘Cleaning Agent’ Neutralizer’ and a ‘Corrosion Inhibitor. You also need a 22mm ‘push fit caps’  for closing off the pipes.

Before power flushing starts is advisable to clean the water tank in the loft. Turn the water off and siphon off the contents with a long hose. The water can be drained into the toilet. The tank may contain a significant amount of sludge. Then close off the tank using a rubber bung to stop water back flowing back up into the tank. Both the vent pipe and the downfeed pipe have to be stopped.

Power flushing starts with isolating the electrical supply. Be careful not to remove the earth continuity bond. Before power flushing you need to remove the central heating pump from the system. Close both of the isolating valves located on each side of the pump. If the power flushing machine come with a connecting manifold you can now connect it to the system. But note that if you have an open ventilated system the mains valve will need to be turned off before the power flushing starts. If there are any problems with a jammed stop cock go to the header tank and tie up the floating ball valve to prevent it refilling

Power Flushing Checklist

  1. Switch the boiler off
  2. Open all radiator valves to their full extent
  3. Fully open the Diverter valve
  4. Cut the water supply
  5. Sealed systems have to be de-pressurized. Water should be drained off to reduce the pressure to atmospheric pressure


One good way to avoid the need for frequent power flushing is to check the loft tank regularly. Power flushing is all about water quality.  Keeping the tank free from sludge will maintain the water quality in the pipes.