hot water heater

Why Is My Hot Water Heater Not Filling Up?

Nothing is worse than stepping into the shower in the morning and getting splashed with freezing cold water when you turn on the hot water faucet. 

Why would your hot water heater tank not fill up? It could be any one of the following reasons: cold water valve turned off, open drain valve, a leak, damaged valve, clogged water line, or the hot water heater is too small.

To learn more about each one of these issues, and how to fix them, keep reading.

Reason #1: Cold Water Valve Turned Off

gas water heater

First and foremost, make sure that water is entering the hot water tank.

If the water doesn’t enter the water heater tank at all, the cold water supply valve may be closed. Ensure that the cold water valve on the top of the tank is in the open position. 

Many valves come with very simple “Open” and “Close” labels on them, and you’ll most likely hear water flowing into the tank. If you still aren’t sure, open valves are parallel with the pipe. 
If water is entering the tank, but it seems to be escaping somehow, you’ll have to diagnose the problem. In order to do that, you need to know what happens after the water enters the tank ?

Reason #2: Open Drain Valve

The drain valve at the bottom of the tank allows water to escape to a nearby floor drain or outside with the help of a garden hose to prevent water damage from occurring every time you need to drain the water heater. 

Draining the water heater is a part of basic water heater maintenance, which you should perform at least once a year. 

If you leave the drain valve open, it will continue to drain the water from the water heater tank, never allowing it to fill up. This will also create serious water waste and increase your water bill. 

You will quickly recognize if the drain valve is open by the water pouring out of the value’s spout. If you notice this, try to close the drain valve.

This should cause the water to stop draining out of the tank and allow it to fill back up. 

Keep in mind that the temperature-pressure relief valve may open and release water if too much pressure builds up inside of the tank to help prevent an explosion.

Reason #3: Leak From A Damaged Valve

Your water heater connects to the plumbing in your house using different connectors and valves. 

If a valve becomes damaged, it can start to leak. Even a small leak can eventually greatly reduce the amount of water in the water tank. 

Some of the common valves that may develop a leak include: 

  • Pressure relief valve (tpr valve)
  • Drain valve
  • Gas valve
  • Inlet valve

The valves on your hot water heater come into contact with water and heat every single day, further expediting the deterioration process. 

Resolving The Problem

Safety first! Always turn off the water and fuel source to your water heater before working on it. 

To resolve the problem, start by tightening all connections with appropriate hardware tools like wrenches and pliers to see if that resolves the problem. If a particular valve still seems to give you trouble, you should replace it with a new valve made out of high-end materials typically found at your local hardware store. 

Reason #4: Clogged Water Line

Hard water creates large amounts of sediment deposits in your plumbing, including your main water line. 

Over time, sediment buildup can clog the water pipes and prevent water from effectively getting through and entering the tank. 

If you have a clogged water line, you will probably notice the flow of water reducing gradually before it stops filling the tank completely. 

Replace Hose 

If you can’t get any water through the clogged hose, you’re going to need to replace the hose completely. 

As always, turn off the water and fuel source to the water heater before you work on it. 

You can choose a new replacement hose between plastic or stainless steel, with stainless steel lasting much longer but coming with a higher price tag. It can also be helpful to pick a flexible replacement hose, especially if you are working in a tight space. 

Reason #5: Leak From Tank

water tank

The average tank lasts between 10-15 years. During this time, it experiences the natural metal degradation process of corrosion. 

Corrosion refers to the rusting of metal over time. Not only does corrosion eat through the tank material, but it also gets rust into your home’s hot water, making it unsuitable for potable water

Anode Rods

Anode rods in the water heater tank help slow down the corrosion process.

There are two types of anode rods: sacrificial anode rods and powered anode rods. Most people use sacrificial anode rods with a metal material that absorbs the corrosive materials and corrode themselves instead of the tank. 

The three types of anode rods are aluminum, zinc, and magnesium. Magnesium anode rods are considered the best option, but they don’t work the most effectively in hard water conditions.

Zinc works the best when you need to remove a sulfuric or rotten-egg smell coming from your water. Aluminum anode rods don’t work as well as magnesium anode rods, but they can withstand hard water better and cost the least. 

You need to change a sacrificial anode rod once it becomes corroded, usually every 2 – 3 years. 

Glass Lining 

Many new water heaters have advanced glass lining that helps them slow down the corrosive process. The glass lining protects the water heater from corrosion and ensures that heat stays inside of the tank, further increasing energy efficiency.

Fixing Leaks From The Tank

If you have a leak in your tank, you need to replace the entire unit.

Some tanks come with a warranty that may cover the replacement water heater as long as you didn’t use excessively high water temperature or hot water pressure. 

To prevent the need to buy another new water heater any time soon, consider upgrading to a tankless water heater. Tankless water heaters last up to 20 years and, as the name would suggest, don’t require a tank at all.

This makes them ideal for small homes that don’t have a lot of space for a large water heater. 

Reason #6: Small Water Heater Tank

If you have a small hot water heater, and multiple people showering one after another or you are running a dishwasher or wash machine at the same time, you will use the hot water faster than it can fill and heat back up.

To make the most of a small water heater tank, it’s best to use low-flow showerheads and reduce how often the hot water runs by limiting time in the shower and how often you use your other appliances. 


Water heater problems can be frustrating, especially if you can’t get any hot water at all. There are a number of reasons that a water heater may not fill up correctly, and you need to properly diagnose the problem in order to move forward with the right solution.

Some of these issues have simple troubleshooting requirements, while others require a complete part replacement or complicated repairs that require the service of a professional plumber or HVAC technician.