The Hot Water Loop That Is Quietly Doubling Your Gas Bill
A recirculation pump is supposed to run on a schedule or on demand. A surprising number of them are simply running all the time, reheating the same water around the clock.
August 26, 2026 · 6 min read
Lucas kept its one-acre minimum lot size, and the houses that got built on those acres are large. So are the ones in Fairview and Parker. In a house that size, the master bath can be a long way from the water heater, and waiting two minutes for hot water gets old quickly.
The fix is a hot water recirculation loop: a pump that keeps hot water moving through the supply piping so it is already hot when you open the tap. It works, it is a genuine convenience, and when it goes wrong it goes wrong invisibly.
How the loop is supposed to work
There are two common arrangements. A dedicated return line runs from the far end of the hot water piping back to the heater, and a pump circulates through that loop. Or, in a retrofit, a valve under the farthest fixture bridges hot to cold so the pump can push cooled water back through the cold line.
Either way, the pump is not supposed to run continuously. It is controlled — by a timer set to household schedule, by a thermostat that runs it only when the loop cools, or by a demand button or motion sensor that runs it when somebody is about to want hot water.
The three ways it fails
The timer fails or was never set
This is the most common one by a distance. The timer loses its program after a power outage, or the pump was installed with the timer bypassed to make it work during commissioning and never restored. The pump runs twenty-four hours a day, and the water heater reheats the entire loop continuously, all night, whether anybody is home or not.
A check valve sticks open
The loop needs a check valve to keep flow going one direction. When one sticks open you get thermosiphoning — hot water circulating by convection with the pump off — and in a crossover-valve system you can get hot water bleeding into the cold line, which is why the cold tap runs warm.
The loop is uninsulated
A recirculation loop deliberately keeps a long run of pipe hot. If that pipe is bare in an attic, every foot of it is a radiator. Insulating the loop is the difference between a system that costs a little to run and one that costs a lot.
What it actually costs
The energy cost is not the pump — a circulation pump is a small motor. The cost is the water heater reheating the loop every time it cools, all day and all night, for a house that is asleep for eight hours of it and empty for another eight.
It shows up as a gas or electric bill that is stubbornly higher than the neighbours' for no reason anyone can identify, and it is often blamed on the HVAC because that is the usual suspect. If your bill is high year-round rather than seasonally, the recirculation loop is worth eliminating before you go looking at the air conditioner.
Getting it right
- Put the pump on a control that matches how the house is actually used — a timer for predictable schedules, on-demand for irregular ones. On-demand is the most efficient by a wide margin.
- Insulate the entire loop, including the return leg. This is the highest-return item on the list and it is often skipped at install.
- Check the check valves if the cold tap runs warm. That symptom is a stuck valve nearly every time.
- On a tankless heater, confirm the unit is specified for recirculation. Not all are, and running a loop on one that is not will short-cycle it constantly.
- While you are there, look at whether the loop needs to serve the whole house. Many were installed to reach one distant bathroom and are keeping the entire hot water system hot to do it.
The tankless wrinkle
Recirculation and tankless water heaters need to be matched deliberately. A tankless unit fires when it senses flow, and a recirculation loop creates a small continuous flow. On a unit not designed for it, that means the burner cycling on and off endlessly, which is hard on the equipment and inefficient.
Units built for recirculation handle this properly, often with a small internal buffer tank. If a loop was added to an existing tankless heater by somebody who did not check, that is worth reviewing.
Family-owned, based in Rockwall, serving Lucas, Fairview, Parker and the rest of Collin County. TX Master Plumber TXM11693, TX HVAC TACLB2360E. (469) 338-5533.
Frequently asked
Why is my cold water tap running warm?
In a house with a crossover-style recirculation system, that is the signature of a stuck check valve letting hot water bleed into the cold line. It is also the reason the system feels like it is working while quietly costing money — the loop is circulating when it should not be.
Is a recirculation pump expensive to run?
The pump itself is not. The water heater reheating the loop is. On an uninsulated loop with a pump that runs continuously, that reheating is a meaningful line on the utility bill every month of the year.
What is the most efficient way to run a recirculation loop?
On demand — a button or occupancy sensor that runs the pump only when somebody is about to use hot water. A timer matched to actual household routine is second best. Continuous operation is the worst of the three by a wide margin and is what most poorly maintained systems are doing.