Tankless Heater Temperature Swings in an RV
If your RV shower keeps shifting from hot to cold, the tankless water heater may not be the only thing to blame.
Tankless systems are sensitive to changes in water flow, which makes them a little more demanding than traditional tank heaters. Even a small drop in flow can cause the burner to cycle off and on.
The result is the classic hot-cold-hot-cold shower nobody enjoys.
First Thing I Would Check
One of the easiest tests is switching from campground city water to the RV water pump.
Disconnect city water, turn on the pump, and test the shower again.
If the hot water becomes steadier, the issue is often related to:
- weak campground pressure,
- a restrictive pressure regulator,
- a clogged filter,
- or reduced flow somewhere in the system.
In some rigs, the pump delivers more stable hot water than campground hookups.
Pressure Regulators Can Cause Problems
Some RV pressure regulators protect the plumbing but also reduce flow more than expected.
That may not matter much with a traditional tank heater, but tankless heaters depend on steady flow to keep the burner running.
Common signs include:
- weak shower pressure,
- temperature swings during the shower,
- better performance late at night,
- or better performance on the RV pump.
Adjustable regulators usually work better than the small inexpensive inline versions.
Too Much Cold-Water Mixing
This catches a lot of RV owners.
It's common to set the heater very hot and then mix in a large amount of cold water at the shower handle.
Sometimes that reduces hot-side flow enough for the burner to shut off briefly.
Try setting the water heater closer to the temperature you actually want and use less cold-water mixing.
That alone can smooth things out.
Check the Simple Restrictions
A partially clogged shower head or filter can affect tankless operation more than expected.
Things worth checking:
- shower head,
- faucet aerators,
- inline water filter,
- city-water inlet screen,
- hose kinks,
- restrictive fittings.
Even minor buildup can reduce flow enough to cause cycling problems.
Campground Pressure Changes More Than People Think
One campground may work perfectly while another causes problems.
Pressure can also change throughout the day depending on campground usage.
Morning and evening are usually the busiest times. If several RVs are showering or using water at once, flow may drop enough to affect tankless performance.
That's one reason these issues can seem random.
Propane Flow Matters Too
Tankless heaters also need stable propane flow.
If propane flow is weak, you may see:
- ignition failures,
- inconsistent burner operation,
- intermittent hot water,
- or E1-type errors.
One RV-specific issue involves the Excess Flow Valve (EFV).
If the propane valve is opened too quickly, the EFV can partially restrict propane flow. The heater may still try to operate, but performance becomes inconsistent.
If that happens:
- shut off propane appliances,
- close the propane valve,
- wait briefly,
- reopen the valve slowly,
- then test the heater again.
Cold Weather Changes Performance
Incoming water temperature makes a big difference with RV tankless heaters.
Very cold incoming water requires more heating time and can reduce overall shower performance.
You may notice:
- lower flow,
- less stable temperatures,
- or shorter comfortable shower times during colder weather.
That's normal with smaller RV systems.
What I Would Check First
Instead of replacing parts immediately, I would start with:
- testing the RV pump,
- checking the regulator,
- inspecting the filter and inlet screen,
- cleaning the shower head,
- and confirming stable propane flow.
A lot of tankless complaints end up being flow-related rather than an actual heater failure.