how to flush a central heating system combi boiler

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How to Flush a Central Heating Combi Boiler

Do you have a central heating system you intend to flush? A common reason for this is the unwanted residue in your radiator. The sooner you get the sludge out of your central heating system combi boiler, the better it will function. Another reason you may want to flush your boiler system is when executing or planning to perform some repairs in the radiator or internal pipes. It's also essential to flush your central boiling system to prevent them from freezing over if you intend to be away for a while, apart from why we also want to dive into how to flush a central heating system combi boiler. Let's get down to the details.

Some signs and reason it may be time for a power flush or a new boiler

  • Increase performance by removing sludge build up
  • To carry out repairs or add extra radiators.
  • If the property is going to be unoccupied or vacant for any length of time
  • Radiators with discoloured brownish water 
  • Noisy or clattering boiler
  • Central heating takes a long time to heat up

Important: Please note, this is a general how to guide that provides an overview of the process. We recommend that any work to your electrical or central heating system should be carried out by a qualified engineer. Still unconvinced?  Check your insurance policy for a clause that invalidates cover if repairs are not carried out by a suitably qualified engineer.

How to Drain a Combi Boiler

It's important to mention that a functioning central heating system is vital for the hot water requirements of your property. Knowing how to drain it is critical to keep it serving you for a long time. Before we get started, we advise not flushing off yourself if you doubt your abilities or lack some knowledge to perform the task. You want to have a professional engineer around to do the draining for you. To prep yourself, look into the following:

  • If your system is sealed, you will need to repressurize it, followed by draining off contents of wasted water to keep the system pressure in atmospheric pressure. You can read more about this in the instructor's manual.
  • Next, you want to cap the feed expansion pipe, the expansion tank, and the cold down feed pipe,
  • There should be a suitable outside drain for the overflow and the dumping hoses.
  • Connect a cleaning fluid to your power flush system.

If your system is sealed, you will need to repressurize it, followed by draining off contents of wasted water to keep the system pressure in atmospheric pressure. You can read more about this in the instructor's manual.

All said, here are the steps you want to check out.

Step 1: Switch of the Boiler

Before you begin the flushing, we advise switching off the boiler when it reaches 45 degrees Celsius. It's a safety precaution. This helps to cool down the hot water to avoid accidental burns or distress. Do not stop earthing for the continuity bond.

Step 2: Connect a Secure Hose to the Drainage Valve

You will need to connect a secure hose to the drainage valve to ensure water drains properly out of your combi boiler. To get this right, identify the radiator at the lowest point in the central heating system. Proper fixing of the hose pipe into the radiator in the property encourages the valves of all radiators to be opened, which in turn flush out water from all radiators. Use a clip to hold the garden hose firmly to the outlet. It helps prevent the hose pipe from slipping off, creating a water mess. The bleed valves will close once the water has drained. If you don't have a hosepipe, a bucket could still do the job. Ensure to shut the valve often once the need to empty the bucket arises.

Step 3: Start Bleeding the Radiators

Real work begins in step 3, where you will need to open the valves to allow water to run through the system freely. There is a way to make water move with speed. Start with radiators found at the top of the building and open the valves of the lower radiator after 15 minutes. If water does not start coming out of the garden hose after a few seconds, you should check for an air blockage. If this is the case, loop up the other end of the garden hose to a cold tap and blast water back to the radiator you want to drain.

Step 4: Open the Drain-Off Valve and Discharge the Water

Your next step would be to open all the radiator valves within your house. Follow this step by opening the radiator valve the hosepipe is attached to and drains the central heating system. The entire process could take up to one hour or more or as little as 20 minutes.

Step 5: Refill Central Heating System with a Combi Boiler

After the above process is complete, you can go ahead and refill your central heating system. The central heating system works efficiently when the pressure is kept at the required levels. Luckily, you should have a loop near the boiler that returns pressure to the combi boiler, thus regulating it. For air trapped in the heating system, get rid of it by bleeding your radiators. Ideally, start with the radiators downstairs as you head upwards. You can open the filling loop once you have successfully removed the air pressure.

Flushing your Combi Boiler

For the reasons highlighted earlier, combi boilers require flushing; otherwise, they could end up malfunctioned and inefficient, costing you lots of money in terms of electricity bills to pay. Cases of malfunctions are like the poor performance of radiators caused by the accumulation of sludge. Consequently, this results in cold areas within your property. To effectively flush your combi boiler, you need a powerful machine that can effectively pump water through the central heating system. The high volume of forced water gets rid of dust specks from your boiler. Power flushers come in different sizes ranging from a 20-liter tank to a 200-liter. A 20-liter power flush is enough for 25 radiators. You can connect the flush system with the central heating system if the flusher comes with a connecting jubilee clip.

The Power Flushing Checklist

In flushing your combi boiler, you need to:

  • Switch off the boiler
  • Ensure radiator valves are fully opened
  • Fully open the diverter valve
  • Disconnect your system's water supply.
  • Disconnect the valve from the radiator and keep the air bleed valve open.
  • Connect the power flush with previous valves that are on the upside tails of the central system.

On the flip side, you can keep the earth bonding until there is no need to remove the radiator. You should disconnect the main valves if your system is open-vented. Sometimes the boiler could get jammed or broken. If this happens, tighten the floating valve in the header tanker to refill the system. 

How Many times should you refill your Combi Boiler?

The recommended time for refiling your boiler is twice a year. Suppose your boiler needs refilling more than twice a year because of pressure or heat, then you need to check with a professional engineer for any underlying issues.

Wrap Up

Flushing your central heating system combi boiler all boils down to knowing the proper flushing procedure to follow. Luckily, you now know how to go about it. If you still find this exercise a challenge doing it yourself, do not hesitate to contact a professional or expert to help you flush your heating system

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