RV Water Heater Not Getting Hot Enough

The Short Answer: Lukewarm hot water in an RV is most often caused by the water heater bypass valves left partly in the winterizing position, which mixes cold water into the hot line. Other common causes are only one heat source working on a dual-fuel heater, low campground voltage slowing the electric element, a mixing valve, or simply using more hot water than a 6- or 10-gallon tank holds.

Start with the bypass valves

Most RVs have two or three valves behind the water heater (inside a cabinet or under a bed) that route water around the tank for winterizing. If one is partly open in bypass, cold water flows straight into the hot line. The labels or a diagram near the valves show the normal position. Set them to normal, run a hot tap until the water is clear of air, and let the tank heat fully before judging.

A faucet that runs hot briefly and then turns lukewarm, with the tank itself hot to the touch through the access door, also suggests a bypass or mixing problem rather than a weak heater.

Is the heater reaching temperature?

Many RV water heaters do not let you choose the temperature. Suburban’s manual for its SW10 models says the thermostat is not adjustable and holds water at about 130°F. Some newer models and other brands have adjustable or electronic controls; check your manual.

If the water at the tank is hot but the shower is not, look at:

• A mixing or anti-scald valve on the hot line or at the shower
• A shower cartridge letting cold cross into hot
• Long runs of uninsulated pipe in cold weather

Gas and electric are separate heat sources

On dual-fuel heaters, the propane burner and the 120-volt element work independently. One can fail while the other keeps the water lukewarm.

If propane does not light, see RV water heater fault light. If electric does not heat, see RV water heater not working on electric. Electric heating is noticeably slower than propane, and low campground voltage slows it further.

Never switch on the electric element unless the tank is full. Suburban’s manual warns that even brief operation without water burns out the element.

Capacity and use

A 6-gallon tank delivers only a few minutes of shower at full flow before it starts mixing in cold water. That is normal. Navy-style showers, a low-flow shower head, or running both heat sources to speed recovery make a bigger difference than any repair.

When to involve a technician

If the bypass is correct, the tank is full, and the water at the tank is still lukewarm after a full heating cycle on one or both heat sources, an RV technician checks the thermostats, element, burner, and controls. Sediment in Suburban steel tanks can also reduce heating; flushing during anode replacement helps.

Related: RV water heater fires up then goes out, Suburban not working on electric, and Atwood electric not working.

Frequently Asked Questions

Q: How long should an RV water heater take to heat up? A: It depends on tank size, heat source, and the starting water temperature. Propane is faster than electric. If the tank is still cool after an hour on a working heat source, something is wrong.

Q: Can I turn up the thermostat? A: On models with a fixed thermostat, like the Suburban SW10 series, no. Do not modify the thermostat or ECO to get hotter water; they are safety controls.