Does it Matter Which Side of the Radiator has Flow and Return?

Understanding your central heating system can mean the difference between sorting issues when they come up yourself, or calling in an engineer. There are many things you can do, such as bleeding radiators or even replacing them, whilst other things such as power flushing will need a professional.

One question you may have about the way your radiators work concerns the flow and return of water in the system, and if it matters which side the TRV (Thermostatic Radiator Valve) is on. To help, here is our quick guide on what radiator flow and return is, and does it matter which side of the radiator has flow and return. Hopefully, by the end of the article, you’ll have a clear answer!

Radiator Flow and Return – What Does This Mean?

When we talk about radiator flow and return, this refers to the way a wet central heating system works in general. If you have a boiler that supplies heated water to your radiators, this is the system you’ll have and is the most common way our homes across the country are heated. Whether you have designer radiators, vertical radiators, or the classic design of column radiators in your home, they all rely on the flow and return of water to work.

If your system has a hot water cylinder, the water used to heat your radiators passes from the boiler to a heat exchange coil that is present in the cylinder itself. The water then flows back to the boiler with a timer controlling this, as well as a cylinder thermostat. It usually also has a motorised valve to help this along, and the water is pumped around when needed by the radiators.

If you have a combi boiler in your home, a similar cycle happens but there is usually no hot water cylinder present. Instead, when you need hot water, the combi boiler works on demand when you turn the taps on, for example, or the radiators. As it’s on-demand, the flow of water will not go through the radiators if your hot water tap is on, but once turned off, the water will return. This is why if you have a combi boiler you may experience cold water in the shower suddenly when someone else turns the taps on in the kitchen!

Overall, radiator flow and return is the cycle of the water entering your radiators and then returning to your boiler. So, does it matter which side of the radiator has flow and return for this cycle to work properly?

How to Tell Which is Flow and Return on a Radiator

It’s quite simple to work out which side is flow and which is return, and you’ll be able to tell when you turn your central heating system on. Both pipes should be cold if the heating has been off for a while, so when you turn it back on, one side will get hotter much quicker than the other.

  • The flow pipe is the one that gets hottest first, as the water is coming from the boiler
  • The other colder pipe side is the return pipe.

Depending on the size of the radiator, it should be easy to tell which is flow and return on a radiator by touching both pipes, for example, on large radiators, as it will take time for the hot water to go through. Smaller radiators may do so much quicker, so you may need to hold both sides to be able to tell in this way.

Radiator Flow and Return Sides – Does it Make a Difference?

Your central heating system most likely has a two-pipe layout, where one pipe carries the water to your radiator and the other returns it to the boiler for reheating. As described above, you can quickly tell which is the radiator flow and return sides when turning on your heating from cold. When it comes to the TRV, many radiators will have this setup on the flow side as this is where the water enters the radiator, however, you can fit this on either side.

Many modern TRVs are bi-directional, meaning they can be fitted to either the flow or return side of the radiator, but some TRVs only work one way. If you are fitting a TRV or replacing one, it’s usually recommended to place this on the flow side to avoid any issue. Generally, if the TRV is placed on the return side, you may hear a louder, vibrating noise when the water goes through. If purchasing a new TRV, check which type it is and if it is bidirectional before fitting.

What if the Radiator Flow and Return Sides are Fitted Wrong?

If for any reason you think the flow and return are round the wrong way, or you discover the TRV is fitted to the return side and making a noise, you should call out an engineer. This is so they can investigate further the issue and whether any changes are necessary. As described above, if you have bi-directional TRVs, then you shouldn’t have a problem if it’s the flow or return side.

If the flow and return pipes are reversed, potentially this could mean your heating isn’t working as efficiently as possible. Sensors within the system may detect the water being cooler, and in a combi boiler, may increase the heat output. This is where it may make more noise or signal a fault with the boiler. During installation, the pipes may have red and blue tape attached to signal which is flow and return to help avoid this.

If your radiators have bi-directional TRVs installed, then the radiator flow and return sides will not matter. It’s handy to be familiar with your central heating system set up, just in case you ever need to address an issue. In most circumstances, it’s best to get an expert to check if anything unusual is happening.

For more information about installing radiators, or if you have any queries, please contact us.

You still have items in your basket

Would you like to checkout?