5 different ways to drain a heating circuit

If you are a boiler user or technician, some of the most useful knowledge for you is to learn how to empty the heating circuit. If the circuit is too full, the pressure will rise. Or you may also need to empty the heating circuit to maintain it, clean it internally, purge it, renew it, change components, etc. Whatever the reason, here we will tell you about several methods of emptying the heating circuit, so you will always find the most convenient for you.

How to empty the heating circuit: 5 methods

The process of emptying the heating circuit does not depend on the brand of the boiler, but on the type of installation. So what we are saying is equally true for emptying the heating circuit of a Roca boiler, a Junkers, Saunier Duval, Vaillant, Ferroli, etc. The important thing is to empty the heating water circuit following the method that best suits your installation rather than your boiler.

1. Where is the heating circuit drain valve located?

The drain cock is the ideal means when it comes to draining the entire heating circuit. The specific location of the heating circuit drain valve will depend on how the installation is carried out. However, in general, the drain valve is located in the lowest part of the installation, and to place it, the floor of the kitchen, terrace, bathroom, or a room that includes heating but that is left is usually chosen, it may be a bit withdrawn or appear hidden. Once you locate the drain key, you just have to open it and wait for the circuit to empty.

2. Let the water come out of the hot water taps

This method is especially useful in cases of old boilers, which were not designed with non-return valves. First you have to close the water inlet of the house. Then open the boiler inlet tap, and open several or all of the hot water taps. In a short time the heating circuit will be empty.02 Kitchen faucet made of stainless steel, completely open

3. How to empty the heating circuit through a radiator

This is not an entirely efficient method, as the radiator petcock (unlike a true drain cock) is located far from ground level, plus it doesn’t have a large flow rate. Draining the heating circuit through a radiator is not the best way if the entire system needs to be drained.

It is only recommended for partial emptying (when air gets into the circuit or when there is overpressure due to excess water). You just have to put a large enough container under the radiator petcock, open the petcock and allow the water to flow out.03 A plumber opens the drain valve of a heating radiator and lets water flow out..jpg

4. Open the safety valve (not recommended)

This method should not be used unless there is no other alternative. The safety valve is very sensitive and is designed to work automatically. It will probably break if you tamper with it. In spite of everything, if it happens that you have to follow this method, it will suffice to open the safety valve and let the water flow out.

5. How to empty a central heating circuit

It is worth considering how to empty a central heating circuit, although it is assumed that this will always be a task carried out by a qualified technician. As you probably already know, central heating is the heating service provided by a boiler or boiler system to a multi-family building or a house large enough to require this system.

A central heating circuit includes or must include a central drain valve. You just have to open it to empty the circuit. It is normal that at some point the central heating circuit has to be emptied, for the same reasons that a normal one is emptied: maintenance, cleaning, repair, replacement of components, etc., either at a general or private level (1 or more families).

Despite the larger dimensions, draining a central heating circuit is not much different from draining a non-central heating circuit. The details are that the neighbours have to agree, because while the circuit is empty there will be no heating, in addition to the fact that after emptying it and doing the work that is needed, it will have to be refilled, and perhaps purged, until it is left as it was.04 One person opening or closing a yellow stopcock.jpg

Especially in the case of old installations, which do not include individual cut-off valves, emptying a central heating circuit is something that will affect everyone. However, there are special methods that allow a particular installation to work without the need to empty the central heating circuit of which it is a part. You just have to look for the plumber who knows how to do it and has the right tools.

Frequent questions

Now we will concisely answer some frequently asked questions related to the topic of this article.

How to clean a radiator heating circuit?

  1. The first thing to clean the heating circuit is to completely turn off the boiler.
  2. Next, it is necessary to empty the installation or heating circuit, following one of the methods that we have oriented in this article.
  3. Now it is time to insert a water pump in the circuit. To do this, the hot water pipe and the cold water pipe must be connected to the two ends of the pump.
  4. Using the pump, insert into the circuit an anti-limescale product dissolved in water, which is indicated for use in heating systems (which does not damage the boiler or the pipes).
  5. Allow the anti-limescale product to circulate inside the installation, in the cycles or for the time recommended by the anti-limescale product container.
  6. Now it’s time to remove the pump from the system and redo the normal connection of the hot and cold water pipes.
  7. Open the hot water taps and the radiator bleeder valves, turn on the boiler, and let the water run until the anti-limescale product is removed from the system and the water comes out clean.
  8. Close the taps and the radiator bleeder valves, and let the system fill with water until the boiler pressure gauge shows the appropriate pressure (it must be between 1 and 1.5 bars, depending on the brand or model of boiler).

After this procedure to clean the heating circuit, and once the system is already full of water, it is not a bad idea to purge the radiators, because in the process air may have entered the system. Let’s see how to do it.

How to empty the water from a radiator?

Purging the radiators consists of extracting water from them until all the air they contain is expelled. This must be done at least once a year, unless the radiators have built-in automatic bleeders. If the bleeders are manual, then they must be opened, for example, at the beginning of the winter season, or after cleaning the circuit.05 Plumber opening a radiator drain cock with a wrench..jpg

So, how to empty the water from a radiator? It is very simple if you follow these steps:

  1. Place a container under the radiator bleeder valve, so that the water does not spill on the floor.
  2. Depending on the type of bleeder, you will need to use either a flathead screwdriver or some kind of wrench. Using the proper tool, turn the bleeder counterclockwise. Water mixed with air or impurities will begin to come out. Let the water run out until it turns clear and no more air comes out.
  3. Close the radiator bleeder valve, and make sure that the pressure has not dropped more than necessary in the boiler. If so, open the inlet faucet and let water in until the pressure normalises.
  4. If you need to purge several radiators, it is best to start with the one closest to the boiler, and move towards the furthest. If the house has more than one floor, you have to start with the upper floor and work your way down.

How to lower the pressure of the boiler?

If you’ve wondered how to lower the pressure in the boiler, the answer is that it depends on what caused the pressure to rise. In the following table we put some of the most frequent reasons that cause the pressure of a boiler to rise, and their solutions.

no apparent causeAllow water to flow through the drain valve or through a radiator.
no apparent causeNeed to purge the heating installation through the radiators.
Excessive water due to faulty or clogged filler tapUnclog or replace the fill valve. Access the filling valves for sale at Suner
Faulty expansion vesselRepair or replace the expansion tank. Access the expansion vessels for sale at Suner
Safety valve faulty or wrongly taredReplace the safety valve with a new one of adequate calibration. Access the safety valves for sale at Suner

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