Turn off the hot water: how-to guide

Need to turn off the hot water? Whether you have a hot water cylinder or a combi boiler, this is normally a very straightforward task. In this article, we’ll discuss how to turn off the hot water in your home.

How to turn off the hot water

The first step for this task is to understand how your hot water system works. Here’s a brief list of the most common configurations:

  • Combi boiler. This is the most common arrangement in UK households. With a combi boiler, there are no cisterns in the loft. Water for both the hot taps and the radiators comes directly from the mains.
  • Hot water cylinder with a cold water storage cistern. This is a very common arrangement. The cylinder is supplied with water from a cold water storage cistern in the loft. The cistern also accommodates for the expansion of the water when it is heated. This type of configuration is known as an open vented cylinder. On some hot water cylinders, the cold storage cistern may not actually be in the loft, and is instead an integral part of the cylinder. Such cylinders are known as Fortic cylinders.
  • Hot water cylinder without a cold water storage cistern. This is becoming more common in UK homes since they were permitted by the water regulations in the mid eighties. An unvented cylinder does not need a cistern in the loft because it is fed directly from the mains.

If you have a combi boiler

If you have a combi boiler, you can turn off the hot water by turning off the mains stopcock. You can usually find the mains stopcock in the vicinity of the kitchen sink. It may be in the cupboard under the sink, or it may be on an adjacent pipe. Turning off mains stopcock will also shut off the water to every outlet in your home.

If you have a hot water cylinder with a cold water storage cistern

Turn off the gate valve on the cold supply pipe to the cylinder. This valve should be easily recognisible as a valve with a red, wheel-shaped handle on a pipe that runs from the ceiling of the airing cupboard to the bottom of the cylinder.

Hot water comes out of the top of the cylinder due to gravity acting on the cold water in the cistern in the loft. Thus, stopping the cold water going in at the bottom prevents the hot water from being pushed out at the top.

This obviously means that even if you turn off the cold supply, the hot water cylinder will still be full of water. This is a safety precaution which prevents the immersion heaters or the boiler from trying to heat an empty cylinder. If you need to drain the hot water cylinder, take a look at the how-to guide for this task.

If there is no gate valve on the supply pipe

Can’t find a gate valve on the supply pipe in the airing cupboard? It may be in the loft on the cold pipe coming from the cold storage cistern.

If there isn’t a gate valve at all between the storage cistern and the hot water cylinder, another solution is to insert a rubber tank bung into the outlet at the bottom of the cistern.

If you have a Fortic cylinder

On a Fortic cylinder, there probably won’t be a gate valve on the cold supply pipe, because the cold supply pipe is probably concealed under the cylinder’s foam insulation. If there is a gate valve on the hot outlet pipe, it’ll be on the pipe coming out of the very top of the hot water compartment. (Should there be two pipes lower than this in line with each other, then these are the flow and return from the boiler, which you can ignore.)

If you have a hot water cylinder without a cold water storage cistern

If you have a pressurised cylinder, you’ll need to turn off the stop valve or isolation valve on the cold feed pipe. You can turn off the mains stopcock if you can’t find this. As previously mentioned, the mains stopcock is usually located near the kitchen sink, perhaps in the cupboard underneath it. Note that closing the mains stopcock will also shut off the water to every tap and outlet in your home.

Getting the hot water back on should simply be a case of opening the valve which you closed. If you have to turn off the mains stopcock, don’t forget to fill up some saucepans with water so you can still make a cup of tea!

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