Central Heating Plumbing

Domestic Plumbing Systems

If you plan to do any work on the plumbing of your home, it is important that you understand the various different plumbing systems and how they work. You don’t need to be a expert on every single part of the system, but having a good overall idea of how things are linked together will make planning your DIY plumbing jobs a lot easier.

Most modern homes have four different plumbing systems:

– Direct or indirect cold water system.
– Hot water system.
– Waste System (wastewater, drainage, etc)
– Hot Water Central Heating System

Not all houses will have all of these plumbing systems, and some will have additional or different systems, but these four plumbing systems are the most common and therefore the systems we will look at in this guide.

Direct or Indirect Cold water System

This plumbing system brings the cold water in and distributes it around your house.

Direct Cold Water System

With a direct cold water system, mains water comes into your house through the Rising main as usual, and then branches off to feed the kitchen, bathroom and any other cold taps. It also usually (but not always) feeds the cold water storage tank in the loft. All of the outlets are therefore fed at mains pressure and as it is mains water, all cold taps are safe to drink from. However, in some older direct systems there is a slight chance of water from the toilet siphoning back into the system and contaminating the system. Newer direct systems will have non-return check valves to stop this happening. The Indirect Cold Water System has been the preferred type for some time now, so Direct cold water systems are now usually found only in older houses.

Indirect Cold Water System

Unlike the Direct System, with a Indirect Cold Water System only the kitchen cold water tap and the cold water storage tank are fed by the rising main. All of the other outlets are then fed, by gravity, from the cold water storage tank in the loft, including the hot water tank and toilet cistern. This means that only water from the kitchen tap is totally safe to drink. An indirect system reduces the risk of water siphoning back from the toilet and also reduces the possibility of noise in the system (such as Water Hammer, where water travelling around tight bends in the pipework causes the pipes to vibrate). With an indirect system, you also have the advantage of a back-up supply of water in the cold water storage tank in the event of a temporary loss of mains supply.

Direct or Indirect Cold Water System?

There are a couple of easy ways to tell if you have a direct system or an indirect system in your house.

1. Age of the property – Most houses built within the last 50 years will have an Indirect System. There are exceptions to this, but the age of the property is a good guide.

2. Toilets – Turn off the stopcock and flush your toilet. If the cistern refills you have an Indirect system.

3. Bathroom Tap – Turn off the stopcock and open the cold tap in your bathroom. If water flows for more than a few seconds, you have an indirect system.

Hot Water System

The hot water system in your house will usually be comprised of three separate major components: the Boiler, the Hot Water Cylinder and the Cold Water Storage Tank. Your house will have either a traditional direct hot water system or a newer style indirect system. It is important, if you are planning to make any alterations, to know if you have a direct or indirect hot water system.

Direct Hot Water

In the direct system, water is fed down to the bottom of the hot water cylinder from the storage tank in the loft. From there it feeds into the boiler where it is heated, before rising back up into the top of the cylinder to be fed into the hot taps in your house. If the hot water is not used, it cools and passes back down to the bottom of the cylinder and is once more fed to the boiler to be heated.

Indirect Hot Water

Newer houses will usually have an indirect system. Indirect systems add a fourth basic component to the system, a feed-and-expansion tank. Both the feed-and-expansion tank and the storage tank feed different parts of the cylinder and from there supply either the hot taps or the central heating system. Each tank has its own pipe run.

Direct or Indirect Hot Water System?

As with the cold water system, there are a couple of easy ways to check if you have direct or indirect hot water system.

1. Extra Water Tank – Have a look in the loft. If there is a second (usually slightly smaller) tank, and each has two pipes, you probably have an Indirect System.

2. Back Boiler – If you live in a older property with a back boiler behind the fireplace, you probably have a Direct System.

3. Boiler – If you have a single, large boiler which fires up when you turn on the hot water tap and when you turn on the central heating, you have an Indirect System.