In RVs, "on-demand hot water" means the water heater can provide an unlimited supply of hot water — but it doesn’t mean you get hot water immediately when you turn on the tap.
1. The water still needs to travel through cold plumbing.
When you turn on the hot water faucet, the water already sitting in the pipes is cold. That cold water needs to be flushed out before hot water reaches the faucet. This can take a few seconds or even a minute, depending on the length of the plumbing in the unit.
2. The heater needs time to fire up.
Most RV tankless systems don't heat water until you actually open a hot water tap. Once you do, there’s a slight delay as the system detects flow, turns on, and brings the water up to temperature.
3. Low flow = No go (sometimes).
Many RV on-demand heaters have a minimum flow rate. If you try to trickle water to conserve it, the system may not even turn on — so you’ll get cold water. You usually need a steady enough flow for the heater to kick in.
4. Temperature fluctuations happen.
RV water pressure can vary a lot, especially on a pump or campground water. These changes can make the temperature fluctuate while the heater tries to adjust — so you might get hot water, but not consistently hot water.
5. Pressure can help control water temperature
If you want the water a bit cooler, turn the hot tap all the way on, as this speeds up the flow, allowing less time in the heater. Conversely, if you want it a bit hotter, you can turn down the flow, allowing more time for the water to be heated before reaching your tap.
6. Avoid the cold water
Turning on the cold tap indicates to your system that you do not want hot water. This may result in the heater turning itself off to accommodate for the cold water being requested. Avoid turning on both the hot and cold taps at the same time.
7. Conserve your water.
Water is valuable, especially if you are not hooked up to a steady water source. If you plan to cook anything with water or are expecting to use some later for other things, fill up a bucket or pot with the water that comes out of the tap while you are waiting for the hot water to come through.
For a helpful video guide, please watch the video below:
