Your RV water heater is working.
Eventually.
You turn it on expecting hot water, wait…and wait…and the water still isn’t ready.
Maybe it eventually gets hot, but it takes much longer than you remember. Or perhaps you can get warm water, but the heater struggles to recover after someone takes a shower.
The good news is that if your RV water heater does eventually produce hot water, you’ve already eliminated several possible problems.
Now the question becomes:
Why is it heating so slowly?
Before replacing the heating element, thermostat, or entire water heater, there are several simple things worth checking.
Safety First
RV water heaters use electricity, propane, or both.
Before opening access panels or inspecting components:
- Turn off shore power and disconnect other 120V power sources before working around electrical components.
- Turn off propane before servicing the burner assembly.
- Allow the water heater to cool before draining or opening the pressure-relief valve.
- Never operate a tank-style RV water heater without water in the tank.
- Never bypass thermostats, thermal cutoffs, pressure-relief valves, or other safety devices.
- If you smell propane, shut off the propane supply and have the system inspected before operating the water heater.
If you’re uncomfortable working with propane or 120V electrical systems, leave those tests to a qualified RV technician.
First: How Long Should an RV Water Heater Take to Heat?
Before troubleshooting, determine whether the water heater is actually taking longer than normal.
A typical RV tank water heater doesn’t produce hot water instantly.
Depending on the tank size, starting water temperature, heater design, and heat source, it can take roughly 20 to 45 minutes to bring a cold tank up to temperature.
Some systems may take longer, particularly when operating on electric heat alone.
Recovery after using some hot water should normally be faster than heating an entire tank of cold water.
Tankless or on-demand RV water heaters operate differently. They heat water as it flows through the unit rather than heating and storing an entire tank.
If you have an on-demand water heater, some of the troubleshooting steps below won’t apply.
Check First: Which Heat Source Are You Using?
Many RV tank water heaters can operate using:
- Propane
- 120V electric
- Propane and electric together
If your water heater normally heats quickly but suddenly seems slow, determine which heat source is actually operating.
This is particularly important on combination propane/electric models.
You may think both systems are heating when only one is actually working.
Quick Decision Tree
Water heats normally on propane but slowly on electric
Check:
- Electric water-heater switch
- Water-heater circuit breaker
- Heating element operation
- Wiring and connections
- Thermostat operation
The electric heating system may not be producing its normal output.
Water heats normally on electric but slowly on propane
Check:
- Propane supply
- Burner flame
- Burner tube
- Air adjustment
- Exhaust/flue area
A weak or poorly adjusted burner can significantly increase heating time.
Water heats slowly on both propane and electric
Check:
- Starting water temperature
- Bypass valve position
- Outside shower valves
- Hot/cold water mixing
- Mineral buildup in the tank
- Thermostat operation
If both heat sources appear to work but performance is poor, the problem may not be the heat source itself.
Water starts hot but quickly becomes lukewarm
This may not be a slow-heating problem at all.
Check for:
- Incorrect bypass-valve position
- Outside shower hot and cold valves left open
- Failed or improperly positioned mixing valve
- Excessive hot-water demand
- Sediment or mineral buildup
Cold water may be mixing with the hot water somewhere in the plumbing system.
Most Common Causes
1. Only One Heat Source Is Actually Working
This is one of the first things I’d check on a combination propane/electric water heater.
If you normally use propane and electric together, the water heater can recover relatively quickly.
But if one heat source stops working, the other may continue heating the water.
That creates an interesting symptom:
The water heater still works—it just takes much longer.
Because you’re still getting hot water, it’s easy to overlook the failed heat source.
Quick Test
Try operating the water heater on each heat source separately.
Run it on propane only and note the heating performance.
Then, after allowing conditions to return to normal, test it on electric only.
If one mode heats normally and the other doesn’t, you’ve narrowed the problem considerably.
2. Electric Heating Element Isn’t Working Properly
On electric-equipped tank water heaters, a heating element transfers heat directly into the water.
If the element isn’t operating, the propane burner may still heat the tank normally.
Depending on the model, possible causes include:
- Failed heating element
- Tripped circuit breaker
- Water-heater switch turned off
- Failed thermostat
- Wiring problem
- Control-board problem
A heating element can also be damaged very quickly if it’s energized while the tank is empty.
If you suspect an electric heating problem, the element and its electrical supply can be tested.
3. Propane Burner Isn’t Producing a Strong Flame
If propane operation is unusually slow, inspect the burner flame.
A healthy burner should normally produce a strong, mostly blue flame.
A weak, lazy, yellow, or unstable flame may indicate a problem with:
- Burner tube
- Air adjustment
- Propane pressure
- Gas orifice
- Obstruction in the burner assembly
Spider webs, insects, dirt, and debris can sometimes partially obstruct burner components.
Important
Do not enlarge or modify the gas orifice in an attempt to increase burner output.
If cleaning doesn’t restore proper burner operation, the propane system should be inspected by a qualified technician.
4. Cold Incoming Water
Sometimes nothing is wrong with the water heater.
The incoming water is simply much colder.
This becomes particularly noticeable during colder weather.
If the water entering the tank starts at 40°F (4°C) instead of 70°F (21°C), the water heater has considerably more heating to do.
That means longer initial heating times and slower recovery after showers.
If the problem only appears during colder weather, incoming water temperature may be part of the explanation.
5. Water-Heater Bypass Valves Aren’t Fully in the Normal Position
This is especially worth checking after the RV has been winterized or de-winterized.
The bypass valves allow you to isolate the water heater when winterizing the RV.
If one of those valves is left partially open or positioned incorrectly, cold water can mix with the hot-water supply.
The heater may actually be reaching normal temperature while the water coming from the faucets feels only warm.
Check the Valve Positions
Make sure the water heater is configured for normal operation rather than bypass mode.
Valve arrangements vary between RVs, so follow the plumbing layout or manufacturer’s instructions for your particular system.
6. Outside Shower Valves Are Open
This one causes more confusion than you might expect.
If your RV has an outside shower with separate hot and cold valves, those valves can sometimes be left open while the shower head itself is turned off.
That can create a connection between the hot and cold plumbing systems.
Cold water then mixes into the hot-water line.
The result can look like:
- Slow water-heater recovery
- Lukewarm water
- Hot water that doesn’t last
- Inconsistent faucet temperature
Make sure both the hot and cold outside-shower valves are fully closed when the shower isn’t being used.
7. Mineral or Sediment Buildup
Over time, minerals can accumulate inside a tank-style RV water heater.
How quickly this happens depends heavily on water quality.
Mineral deposits can reduce heating efficiency and contribute to other water-heater problems.
If the tank hasn’t been flushed in a long time, servicing it may improve performance.
Always turn off the heat sources, allow the tank to cool, shut off the water supply, and relieve pressure safely before draining the water heater.
8. Hot Water Demand Is Exceeding Recovery Rate
RV water heaters are small compared with most residential water heaters.
A common tank size is only around 6 gallons, although larger models are available.
That means there is a limited amount of stored hot water.
Long showers, consecutive showers, dishwashing, and other hot-water use can consume the available supply faster than the heater can replace it.
This doesn’t necessarily mean something is wrong.
If the heater reaches normal temperature when left alone but struggles during heavy use, you may simply be exceeding its recovery capacity.
A Simple Test to Narrow Down the Problem
If you have a combination propane/electric tank water heater, testing the two heat sources separately can tell you a lot.
Test 1 — Propane Only
Start with a cold tank.
Turn on propane heating only and note approximately how long it takes for the water to reach normal operating temperature.
Test 2 — Electric Only
Once you’re able to repeat the test under similar conditions, operate the water heater using electric heat only.
Again, note the heating time.
What the Results Tell You
Propane normal + electric slow:
Investigate the electric heating system.
Electric normal + propane slow:
Investigate the burner and propane system.
Both unusually slow:
Look beyond the individual heat sources—especially water mixing, valve positions, mineral buildup, thermostat operation, or unusually cold incoming water.
This is much more useful than simply replacing whichever component seems most suspicious.
When to Book Service
Consider having the water heater inspected if:
- Heating time has suddenly increased significantly
- The propane flame appears abnormal
- The burner repeatedly shuts down
- The electric heating element isn’t operating
- The circuit breaker trips
- Wiring or terminals show signs of overheating
- Water temperature is inconsistent despite correct valve positions
- The water heater won’t reach normal operating temperature
- You smell propane
Propane pressure, electrical voltage, heater current draw, thermostat operation, and control-board output may require proper testing equipment.
Service Call Prep
Before contacting an RV technician, write down:
- Water-heater manufacturer
- Model number
- Tank size, if known
- Whether it uses propane, electric, or both
- Approximate heating time
- Whether the problem occurs on propane
- Whether the problem occurs on electric
- Whether the RV was recently winterized or de-winterized
- Whether the water is truly cold or simply lukewarm
- Any warning lights or fault codes
Those details can significantly shorten the diagnostic process.
What to Expect During a Service Call
A technician will usually begin by determining whether the water heater is actually heating slowly or whether cold water is mixing into the hot-water plumbing.
Depending on the symptoms, they may check:
- Burner flame
- Propane pressure
- Gas valve operation
- Heating element
- Voltage to the element
- Current draw
- Thermostat operation
- Control-board operation
- Bypass valves
- Plumbing crossover
- Tank condition
The important distinction is whether the heater isn’t producing enough heat or whether the heat it produces is being diluted or consumed faster than expected.
Why Does an RV Water Heater Take Longer to Heat Sometimes?
Heating time depends on more than the water heater itself.
The system has to raise a certain volume of water from its starting temperature to the thermostat’s operating temperature.
Colder incoming water requires more energy.
Electric-only operation may recover differently than propane operation.
Heavy hot-water use continuously introduces cold replacement water into the tank.
And if cold water is accidentally mixing into the hot-water plumbing, the heater can be working perfectly while the faucets still deliver lukewarm water.
That’s why measuring what the water heater is actually doing is more useful than simply deciding that it “seems slow.”
Frequently Asked Questions
How long should an RV water heater take to heat?
Many tank-style RV water heaters take roughly 20 to 45 minutes to heat a cold tank, depending on tank size, starting water temperature, heater design, and heat source. Your manufacturer’s specifications are the best reference for your particular model.
Is propane faster than electric for an RV water heater?
It can be, depending on the water heater. On combination models, using propane and electric together may provide faster recovery than either heat source operating alone.
Can I use propane and electric at the same time?
Many combination RV water heaters are designed to operate both heat sources simultaneously, but this depends on the specific model. Check the manufacturer’s instructions before doing so.
Why is my RV water hot at first and then quickly turns lukewarm?
You may be using the stored hot water faster than the heater can recover, but also check for incorrect bypass-valve positions or hot/cold plumbing crossover.
Can an outside shower cause lukewarm water inside the RV?
Yes. If both outside-shower valves are left open while the shower head is shut off, some systems can allow hot and cold water to mix.
Can hard water make an RV water heater less efficient?
Mineral accumulation can reduce performance over time. Periodic tank flushing and maintenance are particularly important when the RV is frequently supplied with hard water.
Related RV Water Heater Problems
If your water heater isn’t simply taking longer than expected, start with the symptom that best matches what you’re experiencing.
RV Water Heater Not Working on Electric
Start here if the water heater works on propane but won’t heat on 120V electric power.
Water Heater Doesn’t Work On Propane
Use this guide if the electric side works but the propane burner won’t heat the water
Still Not Sure Why Your RV Water Heater Is Heating Slowly?
Don’t replace the water heater just because it’s taking longer to produce hot water.
First determine whether the problem happens on propane, electric, or both.
If only one heat source is slow, you’ve already narrowed the problem considerably.
If both are slow, start looking at water temperature, valve positions, plumbing crossover, mineral buildup, and hot-water demand.
A few simple observations can often separate an actual water-heater failure from a system that’s working normally but under less-than-ideal conditions.
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Written by Dan Harvickson (Founder of Last Mountain Tech) RV Specialist