Draining a Central Heating System: A Simple How-to Guide

Draining a Central Heating System: A Simple How-to Guide

If you’re unsure how to drain your central heating system, check out this simple, yet detailed, how-to guide to learn everything about it.

Whether you’re removing a radiator, fitting a new one, or refilling one, I’ll walk you through the process of draining your central heating system.

It’s worth mentioning that the instructions in this article apply only to open-vented heating systems. So, if you have a sealed one, you should look for a qualified plumber to do the task.

Also, if your heating system has been running for ten years or more, you might want to consider opting for a new one instead of wasting half the gas you buy.

Read on to find out how to shut the valve responsible for the feed and expansion tank, drain your radiator with the help of an outlet on the radiator valve, and refill the heating system again after you’re done.

Draining Your Central Heating System

Firstly, turn off the power supply (be it gas or electricity) that runs your boiler and make sure that all the solid fuel-based boilers are out.

Proceed to lock the ball valve in your feed and expansion tank off, then connect a hosepipe drain nozzle to another radiator downstairs, making sure that you can run it to a good spot outside.

After that, open the drain valve to allow the water to get out of the system and the bleed valves located on the radiators upstairs to facilitate the draining process.

It’s important to prevent your system from becoming fully drained by checking that there aren’t airlocks in it. Once the system is drained (except for the last bit you left), you can proceed.

Refilling Your Heating System Again

Next, let’s talk about the refilling process. Start by closing the drain cock on the radiator and all the bleed valves you’ve previously opened.

After that, undo the string in the feed tank to allow water to fill up the system through the tank and when it stops, go downstairs to start bleeding the radiators on the bottom level.

When you’re done with that step, go upstairs to bleed the top radiators as well to make sure that your system is filled.

Tip: Adding an inhibitor to the system is an excellent way to protect it from corrosion and limescale.

You can switch the power supply on and relight the boiler when you’ve made sure that you’ve tightened all the nuts again and double-checked everything.

You may hear a knock here and there as the water starts heating up and the air expands inside the system. On that note, you might want to give your radiators another round of bleeding when the system is fully heated.

After you’ve done all that and the system heats up to the maximum and reaches full pressure, scrutinise your work again to make sure there aren’t any leaks.

Why is Draining my Central Heating System Necessary?

Draining and refilling your central heating system sounds like a hassle. Not only that, but there’s some danger to it, so why would you do it?

It could be inevitable if you’re trying to clean and flush it through the system to remove sludge by introducing a new agent, or if you want to replace the radiator.

In any case, you must turn off the boiler, be it a gas-powered or an electric one. If it’s a back boiler or solid fuel one, you must take it out.

If you’re looking for more details, let’s delve further into the process.

Expansion and Feed Tank

You’ll find an expansion and feed tank in your loft that you can recognise by a pipe entering it from the top, representing the expansion part of the deal. It serves as a place where the steam can expand with the pipe’s help if the water gets too hot inside the system.

The water from the mains is fed into the expansion tank by a ball valve, which is pretty much the same valve as the one in a toilet cistern. When the water starts to rise, the ballcock is lifted.

You’ll find the ball attached to the arm responsible for closing the valve when it’s lifted; then, it closes when the tank is full to prevent any more water from getting in. If it doesn’t close by any chance, the water is drawn off to allow it to get in when the ball drops.

Also, when you’re draining the system, you can simply put a piece of timber across this tank to prevent the water from coming in. Close the valve by lifting the arm up and tying it to the timber.

Parts of the Tank

When you connect the hosepipe to drain the nozzle and run it outside to a point you find suitable, double-check that the water doesn’t stray to the pavement or road (this applies strongly in the winter) as it could freeze and cause accidents.

With an adjustable wrench, open the drain valve and allow the water from the system to run through. This process could be sped up by opening the bleed valves on the radiators, starting with the ones at the top level.

You can open the ones downstairs when the water level drops.

Parts of the Radiator

When you find that the water has stopped coming out of the hose, it’s important to check that the system has finished the draining process before you start removing the radiators. Sometimes air gets into the system and prevents the water from flowing.

To fix this issue, you might want to go into the loft and loosen the arm you’ve tied up a little by using around 6 inches of water to fill the tank.

In a matter of seconds, your hose would start running again. However, if it doesn’t, this indicates an airlock, so you have to connect the opposite end of the hose to the tap to send some water into the radiator.

How to Drain a Central Heating System – Final Thoughts

Though the process of draining and refilling a central heating system can be a little tough to get around, once you’ve performed the task a couple of times, it’ll flow smoothly and safely.

Got stuck while draining your central heating system? Get in touch with PHS and one of our experts will always be available to advise you further.

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