Skip to Content

Hot Water Heater Not Filling Up [4 Reasons with Solution]

It’s pretty frustrating if your hot water runs out in the middle of a shower. It’s because your water heater is not filling all the way up. 

Why exactly is the hot water heater not filling up?

We have included 4 reasons for this problem. This can happen because of weak pipe joints. A stuck TPR valve can also be blamed. An airlock in the pipe can be responsible too. Also, the problem could be because of the blockage in the pipe as well. 

If this problem is still dizzying for you. We’ve discussed in detail and provided some methods to fix this problem.

Read along to clear yourself out!

Why Is My Hot Water Heater Not Filling Up? – 4 Reasons Explained

Water heater not filling up is a common problem if it is aged. But you may also face this problem with your new hot water heater.

4 reasons why you are facing this problem are described below with solutions- 

Reason 1: Water Leakage

You may notice water around the water tank. It’s just like sitting water in your shower tray. This indicates your hot water heater is not filling up because of water leakage.

It may occur because of some leakage in the pipe. For example, if the connection of pipes is poor, it may lead to water leakage.


You might see the water leaking from the place of connection of your pipe. To solve this, just grab a wrench and tighten the connection of the pipe. 

To ensure a good result you may also use some Teflon tape. It will be working just fine as new. 

Reason 2: Stuck TPR Valve

Your water heater is not filling up because water is draining constantly. It may have occurred because of the TPR valve. 

What if your TPR valve didn’t shut down the way it should be. Water will be draining from the valve. It will cause low pressure in the hot water heater.

If your water heater is old, it’s usually common. But no worries, It can be fixed in no time. 


TPR valves can be clogged and damaged. To fix that, disconnect the water tank from electricity first. Or just shut down the gas line. 

You need to grab a wrench and open up the valve then. Grab a brush to clean up the clogged pipeline and also the TPR valve. You should have a wire brush for this. 

Here we tried to mention some good quality brushes and brushes kit:

Product 1
Product 2

We have listed some of the best brushes and brushes kits in the market. Use them to remove the blockage properly.

Finally, after cleaning, add the valve to the tank and it’s good to go.

You need to use Teflon tape to adjust the pipe. Apply the tape in a clockwise direction. Give it a three to four wrap. Just how you would use Teflon tape on your sprinkler heads

If your TPR valve is damaged on a huge scale, you might need to replace the valve. Be very careful to buy the same matching valve with the same size and psi.

If your TPR pipe is fine, something else may be responsible for this problem.

Reason 03: Airlock in Pipe

Sometimes a pocket of air can be trapped inside the pipeline. The trapped air will hold back the hot water heater from filling up.

You have to determine if this is the problem or not. To do that, open up a hot water faucet in your toilet. 

Check if the water dripping is usual. Sometimes you will notice air bubbles coming out from the faucet.

Air bubbles decrease the water pressure. For that, you will notice slow dripping of water and also some unusual sounds.


Fixing the airlock problem is an easy task. You will just need to grab a garden hose pipe for this. 

The easy way to fix the airlock is to blow the air out. To do that, add a hot water hose to the cold water hose.

Open the cold water faucet. But this will do the trick. The cold water pressure will blow the airlock. 

But if the pipe has a nonreturn valve, it won’t allow the water to force back. 

In this case, grab a size adjustable wrench, open up the pipe. Add the hose below the nonreturn valve. Open water pressure afterward and the airlock problem will be solved.

Reason 04: Blockage in Pipe 

Hot water heaters use water pressure to fill up the tank. But the clogged pipeline around the tank may reduce the water pressure. It’s all the same if you install the heater horizontally.

The low water pressure causes your water heater to not fill all the way up. It is pretty hard to detect the blockage pipe. But here’s a catch, you just need to empty your tank. Look carefully to the bottom of the tank afterward. 

There will be some sediment at the tank deck. It’s probably the sediment that is causing the blockage. 


You can fix this problem with two methods. Both are easy and effective.

You will just need to follow some steps described below the methods. This way the blockage in your pipeline will be fixed in no time!

Method 01 

Use a mixture of hot water, vinegar, and baking soda. The remedy is super efficient and it will surely clear the blockage.

Hot water and baking soda are effective on the clog. The vinegar will destroy it. By the way, there are lots of other uses of vinegar too.

Method 02 

Take a wrench and open your pipeline. Add a pressure pump to your pipeline then. 

The pressure pump will pump water down to the pipeline forcefully. This Will clear the blockage in no time. 

It can still be possible the pipe remains clogged. That’s why before cutting up the pipe, consult a professional.

Tips On Maintaining Hot Water Heater

Facing this problem can be a hassle, But you can easily avoid this problem by giving some tips. Maintaining a hot water heater is quite easy. This way it can be used for ages. 

Some tips are described below about your water heater maintenance-

Tip 01: Drain The Tank

Draining the tank after a particular time helps to remove sediment that causes blocks in the pipeline.

It’s an easy process. Be very careful handling hot water. 

Tip 02: Replace Old Gear 

Appliances like TRP valves, gas gears are more than 10 years old. It’s best to replace those gears.

Tip 03: Yearly Maintenance 

You need to check your hot water heater yearly by a professional. It will help to find out some little flow and to maintain it for years. 

If you follow those tips, luckily you won’t face the problem again.


Question: What happens if you don’t drain your water heater? 

Answer: if you don’t drain your water heater it may corrode more quickly. The sediment also can block the pipeline. 

Question: For how long can you use a water heater?

Answer: A well-maintained water heater can last for 10 to 15 years. It’s best if you replace it by then. Otherwise, it will cost a lot of maintenance.

Question: Can a broken water heater be dangerous? 

Answer: A broken water heater can be dangerous, call a professional as soon as you can. Because this problem can be deadly.


We hope now you know the reasons behind the hot water heater not filling up. 

Contract a professional, if you are unable to fix this problem. It is quite troublesome but still fixable. 

Hope you fix the problem!