Even if you are maintaining the tank, there are high chances you might not know if the water tank gets full, for this reason, we have here a guide on how to make sure your RV hot water tank is full. Typically, the bypass valve is the reason behind RV warm water reservoir not filling up, but there are quite some reasons that might also cause the problem. Besides all this, good maintenance and keeping everything checked doesn’t necessarily mean that your reservoir is full. So, that being said, let us hop into the details.

How to Fill RV Hot Water Heater

Before taking a good warm bath in the RV, you must check the filling capacity of the RV water heater. Don’t worry, filling one is quite an easy task that needs to be done before a checkup. So, there are two processes or ways in which you can fill the RV which are identical to one another. Let’s discuss them;


First of all, you need to make sure that the warm liquid is not present in the bypass mode. When you are connecting a hose to the intake, the liquid starts flowing through it and into the heater.

In case you are filling the RV with fresh liquid, upon turning the pump on, the fresh liquid will start to flow through the pipes. Now, turn the warm faucet in the motorhome and all of it starts to flow out, leaving no air behind.

This process is the same for all the brands and all the types of heaters, whether they are powered by electricity, propane gas, or even both of them. But, an important thing here to keep in mind is that you shouldn’t turn the electric heater on till the whole reservoir gets too full. In another case, if it is on, the elements will start to burn in the heater.

How to Make sure your RV Hot water Tank is full?

How to Make sure your RV Hot water Tank is full

The process is rather simple because, in the first step, you can ensure that fresh liquid is flowing through the lines by turning ON the pump or simply you are safely connected with the liquid from the city. Then, you can turn the shower warm line on and let it flow.

If you are facing the liquid trying to sputter or slit you need to have patience and let it flow. Sometimes your heater comes with a bypass kit, you need to make sure that these valves are not closed because they are forcing liquid around the heater in the plumbing. That’s how you can make sure your RV Hot water tank is full.

Checking RV Reservoir

  • The most reliable and easy way is to use the level gauge but most models don’t come with one. You can effortlessly tell that the RV is going full by watching this gauge.
  • Another way can be listening to the overflow but it can be done when you are filling it through the city inlet.
  • Don’t like both methods? If you have a gravity fill, you can simply listen to the splashback.


Why does the RV warm liquid tank not full up?

The reason might be the bypass valve, either it is partially closed or completely. Depending on the type of system that you are using, you need to make completely sure that the bypass valve is open. There are a few possible reasons;

  • Blockage in the cold inlet port of the heater.
  • Broken Bypass valve
  • Leaking drain Valve

Does the reservoir fill Automatically?

When it is connected to the city supply, the reservoir will fill automatically. In another case, when it is not bypassed, it will work automatically.

Where is the RV water Heater Bypass valve present?

It is present near the heater back, where the cold enters and the hot liquid leaves. There are various types of bypass valves and depending on it you will find three to even a single one. But, finding them is easy.

RV Water Heater Bypass valve


Even if everything is working fine, there is not a visible means to know that the hot RV tank is filling properly. You can either check the bypass valve and set them to in case there is a problem or check all the buttons that are required to be turned on. There are also various valve systems and typically in the oval position. If you turn on the hot faucet and flows in sputters, it means air is flowing inside it. Wait for around one minute, if the liquid gets smooth flow, it means it is filling properly.