Why is my RV water heater not working?

If your RV water heater stopped working in cold weather

This usually happens when outdoor temperatures drop to around 35°F (1–2°C).

At that point, the water supply line often isn’t frozen, so water still flows normally. That makes it feel like the heater suddenly failed.

In most cases, it didn’t.

What’s actually going on

RV water heaters can only raise water temperature by a limited amount.

When the incoming water is near freezing, the heater can’t bring it up to operating temperature fast enough. Many units will either:

• Shut down to protect themselves, or

• Run but never produce hot water

This is a cold-inlet issue, not usually a broken heater.

Check 

Before assuming the heater is defective:

1. Stop trying to restart it repeatedly
   If the unit is in a protective shutdown, forcing restarts won’t help.

2. Check your exact heater model
   Look up whether it has cold-weather limits or freeze protection. Many tankless RV heaters do.

3. Confirm the recommended cold-weather setup
   Manufacturer or dealer support can tell you whether this model requires inlet water warming in low temperatures.

Heat tape

Some RV owners prevent this issue by keeping the cold-water inlet line warmer in cold weather.

If you do this:

• Use heat tape rated for exterior plumbing

• Apply it only to the cold-water supply line

• Do not apply heat tape directly to the water heater or hot-water line

• Add insulation over the taped line for efficiency

• Plug into a grounded outlet

If you’re unsure, skip this step and contact a professional.

Some tankless RV water heaters are not designed to operate reliably in sustained freezing conditions without additional winterization or enclosure heating. In those cases, the solution is environmental, not mechanical.

If your RV water heater stops working during cold weather, it’s often reacting to very cold incoming water, not failing outright.