How to Install Recirculating Pump on Tankless Water Heater – A Complete Guide

A hot water recirculation pump is one of the best things you can install at home. A recirculating pump installed on your tankless water heater or under the sink gives you instant and on-demand hot water. If you want to install the recirculation pump yourself, you must have a basic knowledge of plumbing lines and fixtures.

To help you further, I’ve composed this guide in which I’ve discussed one of the easiest methods to install a recirculating pump on a water heater. This guide answers all the necessary questions that arise in the mind of consumers who want to know how to install recirculating pump on tankless water heater.

How to Install Recirculating Pump on Water Heater?

Before we jump to the installation methods, it is crucial to understand the working of a recirculating pump and its attachment mechanism with your existing plumbing lines.

How Does A Recirculating Pump Work On A Water Heater?

A circulating pump is installed on the water heater while a senor valve is installed on the faucet or shower away from the heater. For the working of a recirculating pump on a water heater, a separate plumbing pipe for warm water is required. In this way, a loop is created from a water heater to the faucet and shower in your home.

The recirculating pump draws back the unused water to the water heater and recirculates the water through this loop.

In this way, you instantly get hot water when you open the tap or faucet. The advanced recirculating pump comes withs sensor valves that automatically shut off once the warm water loop is complete.

Also, they have programmable timers allowing users to set timers. The pump only activates according to the timer settings and saves a lot of energy.

Tools and Materials

To install a recirculating pump on a water heater you require the following tools and materials A complete pump and sensor valve kit is the main thing you must have in hand. Usually, advanced pump kits include everything you need for installation.

Pump kits usually include fully compatible mounting screws, rubber washers, an electric cord, and a 10-feet long plumbing faucet. Also, you will need a pipe wrench or channel-type pliers, screwdriver, bucket, exit pipe, and towel.

Here is that step by step guide on how to install a recirculating pump on the water heater

Turn Off Electric or Gas Supply

The first step is to turn off the gas and electric supply of the water heater. If your water heater is electric, you need to shut off the breaker to which it is installed. Water heaters are usually connected with a 30-amp breaker, and you can easily locate them inside the home.

If your water heater is connected with a gas supply, locate the gas valve that supplies gas to the heater. A gas valve could be of yellow, blue, or red color. Turn the valve so that it faces the gas pipe perpendicularly.

Disconnect the Water Supply

In the next step, you need to disconnect the water supply to the water heater. The valve is located right above the water heater in most plumbing mechanisms. Close this valve to cut off the water supply to the heater.

If you cannot find the valve on the water heater, look at the water tanker in your home. Locate the pipe that is going to the water heater and shut off the valve present on it.

Drain Water from Plumbing Lines and Water Heater

Before installing a recirculating pump on your water heater, it is advised to drain all the water present in existing plumbing lines. Open the tabs, facet, and showers, flush all the hot or cold water already present in the pipes. The best way to do this is to open the lowest outlet in the home.

However, you can open multiple faucets to drain the water quickly. After draining all the water from plumbing lines, flush out water from the water heater. You can locate the drain valves on the water heater on the back or bottom.

Connect the Pump

Once you are done with all the steps mentioned above, it’s time to connect the pump to the water heater. The recirculating pump is connected via a threaded nipple. The pump’s inward outlet should be installed on the connection that is directed towards outward flow. You may need a Teflon tape or rubber gasket depending upon the type of threaded nipple and plumbing lines present in the home.

Also, it is advised to read the instructions provided by the pump manufacturer carefully. An over-tightened or under-tightened pump will not work properly, so make sure you have fixed it correctly. Also, make sure that the timer is facing in a direction that can be adjusted easily.

Connect Hot Water Pipe with Pump Outlet

Now it’s time to connect the additional pipe for warm water in your plumbing lines. This warm water pipe is directly connected to the pump’s outward outlet. The warm water pipe is usually delivered with the pump, and you get all the nuts and gaskets required in the process.

Remove Air from Plumbing Lines

Since the water supply is disconnected from the water heater and faucets, the plumbing lines will be filled with air. Before we close the loop, it is critical to remove the air from the plumbing line. Open the water supply to the water heater and to all fixtures in the home. The air in the piping will be automatically replaced by water.

Connect the Sensor Valve

Once the air is removed from plumbing lines, you can close the loop by installing a sensor valve. The sensor valve is installed under the sink that is farthest away from the water heater.

Locate the sink furthest away from the heater and look for the valves present under the sink. Under every sink, you can find two valves, one for hot water and another for cold water.

Before you install the sensor valve under the sink, shut off both cold and hot water supply valves. Now disconnect the flex pies from stop valves.

Now check if the sensor valve size and flex pipe size are some or not. In general, there are two flex pipe sizes available in the USA, ½ inch or ⅜ inch.

If they are not of the same size, you can easily buy a new flex pipe or an adapter of the required size from a nearby hardware store. Now connect the hot and cold water supplies to the top inlets of the sensor valves.

In the next step, connect the flex pipe to the bottom outlets of the sensor valve. One senor valve is enough for a small household and ensures a warm water supply for up to three outlets in the home.

However, if you have a big house and branched plumbing lines, you may need to install more than one sensor valve at multiple sinks. Once the valve is fixed with water inlets and flex pipes, you can mount it to the nearby wall using mounting screws. Always use the fully compatible mounting screws that are delivered with the recirculating pump.

Check for Leakage

Before you plug in the power supply of recirculating pump, check for leakage throughout the loop. Open the water supply on all facets and make sure there is no leakage. If you observe any leakage, fix it before you plug in the power supply. A leakage in the loop can cause irreparable damage to the pump when connected to the power supply.

Turn On the Heater

Plugin the power cord into a nearby power supply and program it as per your requirements. Advanced recirculating pumps like Watts 500800 offer a 24-hour fully programmable timer. You can set the timer for any two times a day. Also, on weekends, you can set it to recirculate warm water every fifteen minutes to ensure a flawless warm water supply all day.


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Where do you put a hot water recirculating pump?

A hot water pump comprises two parts, the pump itself and the check/sensor valve. The pump is installed on the water heater’s warm-water outlet. The sensor or check valve is installed under that sink that is located farthest away from the water heater.

Do you need a check valve on a recirculating pump?

Yes, a check valve is necessary on a recirculating pump. Whenever you install a new zone or loop to an existing plumbing line, installing a check wall at the end of the loop is critical. A check valve maintains and regulates the flow throughout the loop.

Should a check valve be before or after the pump?

A check valve is installed at the end of the loop, usually after the pump. The primary purpose of the check valve is to prevent backflow from downstream when you shut off the pump. Therefore it should be installed after the pump.

Final Thoughts

I hope this step-by-step guide will help you install the recirculating pump on the tankless water heater. You can easily install a recirculating pump on the water heater if you have already installed recirculating plumbing lines in your home.

In other cases, it will take you too long to install recirculating flex lines, and it is advised to seek professional help. This is the easiest method one can adopt to install an advanced recirculating pump on a water heater. However, if you have outdated plumbing lines or an old pump model, you may need additional help during installation.

With years of experience under his belt, Adam decided to put his water heater knowledge to work. By providing high-quality content and expert guides, Adam hopes to help anyone looking for expert water heater advice.