Installation of Hot Water Recirculation Pump / Recirculation

In a standard system, hot water runs from the cylinder to the taps through a single pipe. When nobody uses it, the water in that pipe cools down. Recirculation adds a second return pipe that runs from the furthest tap back to the cylinder. A pump on this return slowly pushes the water round the loop, so the pipework stays warm.

It makes most sense where:

• Bathrooms or the kitchen are a long way from the hot water cylinder
• The house has several floors or several bathrooms
• You often run cold water down the drain while waiting for hot
• The pipework is being renovated anyway and a return pipe is easy to add

In a smaller flat with short pipe runs the benefit is usually small. If your block of flats has central hot water, recirculation is normally the responsibility of the building management or owners' association. Do not touch the shared risers without their agreement.

In a new build, recirculation is planned together with the rest of the plumbing. When it is added later, the first question is whether a return pipe can be run at all, and along which route. A typical job looks like this:

1. Assess the existing pipework: the route, pipe sizes, condition, and whether the cylinder has a secondary return connection.
2. Plan the route of the return pipe and the pump position, usually in the plant room or airing cupboard next to the cylinder.
3. Shut off the water, drain the affected section and switch off the water heating.
4. Run the return pipe and connect it at the furthest taps or at the end of the hot water run.
5. Fit the pump with isolating valves on both sides and a non-return valve, plus balancing valves on longer or branched systems.
6. Insulate both the hot supply and the return pipe.
7. Refill the system, bleed out the air and carry out a pressure test for leaks.
8. Connect the pump to the electricity supply and set up the controls.
9. Check that it works under real use, at every bathroom and in the kitchen.

Simply swapping an old pump for a new one usually takes a few hours. Adding a return pipe during a renovation can take a full day or more, depending on how much chasing out and making good is needed.

Many homeowners do not realise this: a pump for domestic hot water is not the same as a central heating pump. Recirculated hot water is drinking water that contains oxygen, so the pump body must be made of a material suitable for potable water, usually bronze or stainless steel. A cast iron heating pump would quickly rust in this kind of loop.

As for size, a small, energy-efficient pump is normally enough for a family home. An oversized pump does not add comfort. It only brings more noise, higher heat losses and faster wear on the pipework.

You can choose between these types of control:

• Timer control: the pump runs, for example, in the morning and evening when the household uses most hot water
• Temperature control: the pump switches on when the water in the return pipe drops below a set temperature
• A combination of timer and temperature, which is a sensible choice in most homes
• On-demand start with a push button or through a smart home system

Why not skip the controls and let the pump run all the time? Because the whole loop then loses heat constantly and the boiler or heater has to keep topping it up. Good controls keep the comfort and cut out most of the pointless running.

In a sealed system with a non-return valve, the cylinder also needs a safety relief valve and often an expansion vessel approved for drinking water. It absorbs the expansion of water as it heats and protects the pipes and fittings.

How much work is involved depends mainly on whether the return pipe is simply added to prepared pipework or has to be run from scratch.

• It is easier with a cylinder that already has a return connection, accessible pipes in the plant room, and pipework running above a ceiling or in a service duct
• It is harder when pipes are buried in walls and floors, which means chasing out channels and then repairing plaster or tiles
• A house with several branches needs more work, because each branch has to be balanced with valves
• Old steel pipes may turn out to be furred up, so part of the pipework may need replacing

A fixed connection of the pump to the mains or to the boiler controls is a job for a qualified electrician. If the work involves a gas boiler, only a qualified, registered gas engineer may work on it. A recirculation loop in a family house does not usually need building permission, but for a larger renovation check with your local building authority under the local building regulations.

These mistakes come up again and again in practice:

• A missing or wrongly fitted non-return valve, so water flows the wrong way round the loop and mixes
• A central heating pump used instead of a pump for drinking water
• An uninsulated return pipe, which in effect heats the walls
• A pump with no controls that runs day and night
• A pump fitted where nobody can reach it for servicing
• Water in the loop kept too cool, which raises the risk of Legionella bacteria

On the last point: lukewarm water that keeps circulating is ideal for bacteria. That is why it is generally recommended to keep the stored hot water at around 60 °C and the water in the loop at roughly 55 °C or above, and, where the heat source allows, to heat the water up higher from time to time. Set the exact values according to the cylinder manufacturer's instructions and the relevant EN standards and local guidance. If small children or elderly people live in the house, ask the installer about thermostatic mixing valves at the taps to prevent scalding.

When you take over the work, check that:

• Hot water arrives almost immediately at the furthest tap
• The pump runs quietly, without humming or vibration
• All joints are dry and a pressure test has been carried out
• The pump has isolating valves on both sides and a non-return valve
• Both the hot supply and the return pipe are insulated
• The controls are set to match your daily routine and you know how to change them yourself
• The water temperature in the loop is not set unnecessarily low
• You have received the pump manual, the warranty and a description of how it is connected