RV Tankless Water Heater Not Hot Enough? The #1 Mistake Almost Every Owner Makes

Is your RV tankless water heater not getting hot enough or going hot and cold? Discover the #1 mistake RV owners make and the simple fix that solves most problems instantly.

If your RV tankless water heater isn’t getting hot enough, keeps going hot and cold in the shower, or takes forever to warm up, you’re not alone.

In fact, this is one of the most common RV service complaints in North America.

But here’s the surprising truth, our expert, Josh the RV Nerd, sees this pattern constantly through real-world service data collected by RVFix. And once owners make one simple change, the problem usually disappears.

Let’s break it down in simple terms.

Table of Contents

Why RV Tankless Water Heaters Work Differently
The #1 Mistake
The Correct Way to Use an RV Tankless Water Heater
Why Your Tankless Shower Goes Hot and Cold
Why it Takes So Long for Hot Water to Reach the Bathroom
Tankless Water Heater and Boondocking
Normal Things That Aren’t Problems

Why RV Tankless Water Heaters Work Differently Than Home Systems

Many RV owners search:

• “Why does my RV tankless water heater take so long?”
• “Why does my RV shower go hot and cold?”
• “Is my RV tankless water heater broken?”

Most of the confusion comes from one key difference:

RV tankless water heaters do not store hot water.

Unlike traditional RV or residential tank heaters:

• They are propane-only
• They only turn on when water is flowing
• They heat water instantly as it passes through the unit
• When no faucet is open, they are completely off

This design is lighter, more efficient, and can provide unlimited hot water, but it requires using the system differently.

The #1 Mistake: Mixing Hot and Cold at the Faucet

At home, you’re used to:

• Turning on hot
• Adding cold
• Adjusting both until it feels right

That works with tank heaters.

Here’s why:

When you mix cold water at the faucet:

• You reduce water flow through the heater
• The heater may drop below its minimum flow requirement
• The burner throttles or cycles off
• Water temperature becomes unstable

This causes:

• Lukewarm water
• Hot/cold/hot/cold temperature swings
• The feeling that the heater “can’t keep up”

The Correct Way to Use an RV Tankless Water Heater

This is the fix that solves most RV tankless water heater problems:

Step-by-step:

1. Turn on hot water only
2. Let it run for a few seconds
3. If it’s too hot or too cold:
   • Adjust the temperature on the heater’s control panel
4. Leave the faucet alone after that

Most owners quickly settle into:

• Shower = hot only
• Sink = hot only
• Drinking water = cold only

Your faucet becomes an on/off switch, not a temperature control.

Why Your RV Tankless Shower Goes Hot and Cold

If you searched:

This is almost always caused by:

• Mixing cold at the faucet
• Or another fixture briefly using water
• Or dropping below minimum flow rate

Tankless systems react instantly to flow changes, so stability depends on consistent water movement.

Why It Takes Longer for Hot Water to Reach the Bathroom

Another common search:

The answer is simple, you are waiting for the cold water in the pipes to clear out.

The farther the fixture is from the heater:

• The longer it takes for hot water to arrive
• The more water is wasted in the process

The heater itself heats instantly.

Is an RV Tankless Water Heater Bad for Boondocking?

This is an important and honest consideration.

Tankless systems can use more water when:

• The shower is far from the heater
• You’re waiting for hot water to reach the fixture

That’s why:

• Full-hookup campers usually love tankless systems
• Boondockers should pay attention to heater placement in the RV

Other Normal Things That Aren’t Problems

These are normal behaviors:

• Slight delays before hot arrives
• Burner noise changing
• Minor temperature shifts when someone uses another faucet

None of these mean your RV tankless water heater is failing.

Why This Matters (And Why Bish’s Talks About It)

At Bish’s RV, thousands of real service calls reveal the same truth:

This leads to:

• Unnecessary service appointments
• Frustrated customers
• Perfectly good heaters being blamed
• And bad experiences that could have been avoided in five minutes

That’s exactly why Josh and the RVFix team share tips like this.

A small change in how you use the system can:

• Eliminate temperature complaints
• Make showers consistent and predictable
• Reduce water waste
• Make your RV feel dramatically more “normal”

Quick Answer Summary (Featured Snippet Section)

How do you use an RV tankless water heater properly?

• Set temperature at the control panel
• Use hot water only at the faucet
• Do not mix in cold water
• Expect slight delays based on plumbing distance
• Once set, stop adjusting it

Quick Takeaway

If your RV has a tankless, on-demand water heater:

• ✅ Set temperature at the control panel
• ✅ Use the hot knob only
• ✅ Expect small delays based on plumbing distance
• ✅ Once dialed in, stop adjusting — it just works

And if questions come up, that’s exactly what RVFix and the Bish’s RV team are here for!