Shut off and drain the water heater's hot outlet, thread the pump onto the heater's hot outlet with the flow arrow pointing toward the house, then mount the bypass valve under the faucet farthest from the heater. Grundfos says to use only the supplied flex hoses and no thread sealant on the valve.
What comes in the kit, and how does it work?
### What comes in the box?
Grundfos lists the contents of the kit this way:
| Item | Detail |
|---|---|
| Circulator pump | Grundfos UP15 with a 24-hour timer and line cord |
| Bypass valve | Under-sink valve |
| Screws | Two valve mounting screws |
| Flex hoses | Two, sized 1/2-inch FNPS x 1/2-inch FNPS x 12-inch. The valve steps below also name 1/2-inch x 3/8-inch hoses. The manual lists both sizes, so use the hoses in your box. |
| Paperwork | Installation and operating instructions |
Before you install anything, Grundfos says to check that the product matches your order and that its voltage and frequency match the installation site. It also says to look for shipping damage and to avoid dropping the pump, because dropping it will damage it.
The pump's power cable goes into a 115 volt outlet. The manual says the pump is for indoor use only, and that it has not been investigated for use in swimming pool or marine areas. Its grounding conductor must go only to a properly grounded, grounding-type receptacle.
### How does the system work?
Grundfos describes the Comfort System as a way to bring hot water quickly to the hot-water faucets in your home. It uses the existing cold-water line as the return path, so no separate return line is needed. It also needs no electrical power under the sink. Water flows from the water heater through the pump, through the hot-water supply line, and back to the water heater through the existing cold-water line.
ENERGY STAR describes the same return path for what it calls an integrated loop system: hot water is recirculated intermittently and returned to the water heater through the cold water pipes. It says this raises the temperature of the cold water slightly, and that it returns to the usual cold temperature in a short time. In a recirculating system, the cooled water sitting in the hot line goes back to the water heater instead of down the drain. We cover that effect in our page on why a recirculating pump warms the cold water lines.
Grundfos says the Comfort System is intended for indoor residential potable drinking water use only, and is to be considered where there is no hot-water return line available. If your home does have a dedicated return line, read our page on whether a Grundfos recirculation pump needs a return line first.
How do you install the pump on the water heater?
Grundfos gives nine steps for the pump. Turn the power off first. The manual warns of electric shock and says not to switch on the power supply until the product has been properly installed.
- 1Close the water supply valve to the water heater. Grundfos says this valve is typically located above the water heater on the cold-water inlet.
- 2Drain the hot-water pipe. Open a faucet in the house and let the water run until it stops flowing. Then drain the remaining water from the water heater spigot. Leave the faucet open until the pump installation is complete. If water does not stop flowing, check that the water to the heater is completely shut off.
- 3Disconnect the hot-water pipe from the hot-water outlet of the water heater.
- 4Install the pump on the water heater outlet. Use the 3/4-inch female fitting and gasket supplied on the pump. The pump shaft must be horizontal. The pump must pump away from the water heater, toward the house, so follow the flow arrow on the side of the pump housing. Grundfos also says the pump must not touch the exhaust vent pipe of a gas- or oil-fired water heater.
- 5Connect the hot-water line to the pump's 3/4-inch NPT outlet. Use pipe joint compound or Teflon tape on the threads of a 3/4-inch female NPT connection. If you use a gasketed flexible copper water-heater connector, neither is required.
- 6Reopen the water supply valve and let the water run until all the air is purged from the pipes.
- 7Close the faucet inside the house.
- 8Plug the pump into a 115 volt outlet. Route the cable so it does not touch the exhaust vent pipe of a gas- or oil-fired water heater.
- 9Set the timer. Grundfos suggests running the pump around your peak use times, such as 30 minutes before the first shower until 15 minutes after the last shower.
Our page on how to set the timer on a Grundfos Comfort System covers step 9 in detail.
### Which way should the pump face?
The direction matters because the pump moves water in one direction only. Grundfos says the water travels from the heater, through the pump, into the hot-water supply line. If the flow arrow points at the heater instead of toward the house, the pump works against the plan. Check the arrow before you tighten the fittings.
How do you install the bypass valve?
The valve goes under the sink where hot water takes the longest to arrive. Grundfos says that, for the greatest effect, it must be located beneath the faucet with the greatest pipe distance from the water heater. If your home has a branched hot water line, more than one bypass valve may be necessary.
### How do you disconnect the risers?
- 1Close the angle stop valves for hot and cold water below the sink.
- 2Disconnect the risers.
Grundfos notes that hot water is typically on the left side and cold water on the right when you look at the sink. Confirm this at your own sink before you connect anything, since a swapped hookup would send the wrong water to the wrong side.
### How do you connect the valve?
- 1Connect the 1/2-inch x 1/2-inch flex hoses to the ports marked HOT OUT and COLD OUT.
- 2Connect the 1/2-inch x 3/8-inch flex hoses to the ports marked HOT IN and COLD IN.
- 3Connect the 1/2-inch hose fitting from HOT OUT to the left side of the faucet.
- 4Connect the 1/2-inch hose fitting from COLD OUT to the right side of the faucet.
- 5Connect the 3/8-inch hose fitting from HOT IN to the left angle stop valve.
- 6Connect the 3/8-inch hose fitting from COLD IN to the right angle stop valve.
- 7Open both angle stop valves and check for leaks.
- 8If you like, mount the valve to the wall with the supplied screws, using the two-hole bracket flush with the wall.
Three warnings apply to this part of the job. Grundfos says not to use Teflon tape or pipe joint compound on the valve threads. It says to tighten the flex hose connections by hand plus 1/4 turn with a wrench, because overtightening can damage the valve, causing it to leak and cause localized water damage. And it says to use only the flex hoses in the kit, because other hoses could damage the valve and void the product warranty. Our page on the Grundfos Comfort System warranty covers what the warranty says about installation.
How do you check that it works?
Grundfos gives a four-step test once the pump is plugged in:
- 1Close the angle stop valve for the cold water below the sink.
- 2Open the cold-water faucet.
- 3Check that the flow of cold water gradually decreases and stops as the bypass valve closes.
- 4Turn on the hot-water faucet and check that hot water begins to flow quickly.
If the test fails, Grundfos's fault table points to the valve first. For "no hot water at the faucet or too much hot water on the cold water side," it lists an improperly installed valve as the cause, and says to review the bypass valve installation and reinstall the valve if necessary. If the pump does not run at all, Grundfos lists three causes: the pump is not connected to power, the circuit breaker has tripped, or the pump is defective.
### Why is there warm water in the cold line?
Grundfos warns that after installation you may find some warm water in the cold water line at the sink where the valve is installed. It says the warm water will dissipate in a very short time once the cold water line is opened. It also points to scalding: the manual says to pay special attention to the risk of injury caused by scalding hot water.
### What are the limits of the kit?
A few limits are worth knowing before you buy or install:
- Indoor use only. The manual says the pump is for indoor use only.
- Potable water only. It is intended for residential potable drinking water. Grundfos says not to use it for flammable, combustible or explosive liquids such as diesel oil or gasoline.
- A running pump needs water. The pump is lubricated and cooled by the liquid it moves, so water must be allowed to circulate through it while it runs. Grundfos also says to make sure the system is filled with liquid and vented before starting.
- Maintenance. Grundfos says the Comfort System is maintenance free and that no service is required.
ENERGY STAR adds a general caution: recirculation systems that operate continuously have the potential to use more energy, due to energy spent pumping and hot water energy lost from the pipes, than the energy saved by reducing hot water waste. The Department of Energy's building science site says the best way to operate the pump is to use demand-initiated controls. The timer in the kit is how you limit run time. Our page on whether a recirculation pump is worth it walks through that tradeoff.
When should you call a plumber?
Several parts of the job reach into your plumbing: draining a water heater, disconnecting its hot outlet, and working on angle stop valves that may be old. Call a plumber if a shut-off valve won't close fully, if a stop valve leaks when you turn it, or if you have a branched hot line that needs more than one valve. HQ Plumbing & Air is licensed and insured, gives free estimates, quotes an upfront price, and offers 24/7 service. If your hot water only works when a pump runs, see why you get no hot water unless the recirculating pump is running.