Why Does My Hot Water Heater Only Runs Lukewarm?

Ossiana Tepfenhart
by Ossiana Tepfenhart

If you’re anything like me, there’s nothing that is better at night than experiencing a nice hot bath. We often don’t give our water heaters enough credit in that department, or appreciate how much they do until we notice that things aren’t doing too well in that department. Having your water running lukewarm might be okay if you’re in the kitchen, but it’s still pretty bad when you’re trying to run a bath and should be cause for concern. Ever wonder what could cause this?

There are four reasons why you might have this issue happen. It’s often a matter of a malfunctioning heating system, a broken dip tube, or sediment buildup in the tank. If you live in a particularly cold area, there is also a slight chance that you might be dealing with water that’s just being cooled down by the cold surrounding piping as well.

Trying to figure out what’s going on with your water heater can be frustrating, especially if it’s in the middle of winter. Thankfully, you don’t need to know too much DIY plumbing to be able to troubleshoot it yourself…or at least get a good idea of what you should expect to hear from a plumber. This guide will help you out.

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Why Would My Water Only Run Lukewarm?

Lukewarm water is great if you have a need for it, but not when you’re in need of piping hot stuff. If you’re dealing with a tap that only runs lukewarm, check for the following issues:

  • Broken Dip Tubes
  • Sediment Buildup in Your Heater
  • A Malfunctioning Heating System
  • Extreme Cold

To help you understand how each issue can affect your water temperature, let’s break it down for you, problem by problem.

Broken Dip Tubes

Dip tubes sound like they belong in a car, but the truth is that they’re actually part of the water heater. The dip tube is the part of the heater where cold water enters the heater. When it’s properly functioning, the dip tube will push cold water down to the bottom of the tank where it can heat up quickly.

If it’s broken, the water won’t get that same amount of pressure. Rather, it’ll simply trickle the water down, which will leave it up at the top. The problem here is that water will only be able to heat quickly at the bottom of the tank. This leaves your water temperatures higher than they should be.

Unless you wait a long, long time to get your water heated, you will end up with lukewarm water. A dip tube can even cause heat problems despite long waits. The good news is that this is a fairly easy fix. All you need to do is replace the dip tube.

Sediment Buildup In The Heater

If you read our article on why water heaters could leak from the bottom, you probably are well-aware of the fact that sediment is bad news. Like, really bad news. If your heater is old, the sediment can corrode the heater from the inside, causing leaks. If you have this happen, it can lead to a need to replace things.

Newsflash! Sediment buildup can also cause other problems. When you have a lot of sediment that hasn’t fully started to corrode everything, the sediment can congregate at the bottom of the tank. This, in turn, makes it harder for the water to heat up at the bottom.

Fixing this can be a little tricky. Flushing out your water heater can help get rid of some of the sediment, but not all of it. To reduce sediment issues even more, switch out your anode rod.

Malfunctioning Water Heating System

One of the easier problems to notice is if your water heating system is just not working. What we mean by that is that your actual heater may be busted. When the part that actually heats the water is not functioning properly, chances are that you will get lukewarm water at best and cold water at worst.

There are several parts that can malfunction here, including the thermostat, thermal switch, and the actual heating element. All three can cause lukewarm water, and you might to have a plumber switch out some parts to keep the water heater going. A professional diagnostic is also necessary.

Since having a water system malfunction isn’t an easy fix, a licensed plumber will be your best route. If you are talented with DIY plumbing, replacing the heating element, thermostat, and switch might be a good way to get rid of all three issues in one swoop. However, this isn’t advised by most DIY gurus.

Extreme Cold

If you’re dealing with lukewarm water in the middle of the winter, there is a possibility that the water is cooling down on the way to your bathtub. However, there are several things that need to line up for this to be true:

  • You have a larger house. If your water heater is a long way away from certain taps, this could increase the chances of cold affecting water temperatures. The larger the house is, the more time it takes water to travel through piping, which can lead to a cooling issue. If you live in a one-bedroom condo with the heater located inside your unit, cold is not going to be what made your water lukewarm.
  • Your home has heating problems. A home that feels nice, warm, and cozy will not have extreme cold as a reason for water being lukewarm. It needs to be pretty chilly inside the house for this to happen in most cases.
  • It has to be extremely cold outside. For the cold to be bad enough to affect water temperatures inside your house, it usually has to be incredibly cold outside. If your area isn’t in temperatures below freezing, chances are that cold doesn’t really explain why your water heater is only lukewarm.

If this is the cause of your cold water, then the best thing you can do is improve your indoor heating setup. Aside from that, there’s not much you can do aside from wait until the cold weather stops being such a huge issue.

When Does Lukewarm Water Mean You Need To Replace Your Water Heater?

In the vast majority of cases, getting lukewarm water instead of hot water doesn’t mean your water heater is dying. In most cases, it’s possible to fix the issues with your heater by replacing one or more of the parts that keep your water flowing warmly. So, there’s no need to panic about buying a new heater.

How Much Will It Cost To Fix My Water Heater?

Well, it depends. The price it takes to replace a dip tube or a thermal switch will be far less than what it takes to replace the full heater. In most cases, the repairs you’ll need to make will cost under $300 if you do them yourself. Calling a plumber, of course, will be pricier due to labor costs.

How Long Does It Take To Repair Most Of These Issues?

Here’s another slice of good news for worried homeowners. If you were worried about going for days without a heater, don’t be. Most of these repairs can be done in a couple of hours, tops. So as long as you fix the problems, you should be able to enjoy a piping hot bubble bath later that day.

Should I Replace My Water Heater?

With most cases involving lukewarm heating, there’s no need to replace your heater. It’s usually a quick fix, and it can even happen to water heaters that are more modern. However, there are always times when this problem could be the straw that broke the camel’s back.

Most water heaters should be replaced around the time when they get between 10 to 15 years in age. This is because that’s the time they become increasingly unreliable and less likely to be able to function without serious revamping.

A good indicator that it’s time to change your heater is if you regularly field problems with it, or if this isn’t the only issue you’ve had. If getting lukewarm water is the least of your issues, then yes, it might be a good idea. Otherwise, just give it a fix.

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Our Final Take

If you’re like most people, getting lukewarm water when you want hot is more than a pet peeve. It’s a major cause for concern about the wellbeing of your water heating system. We get it! Water heaters are not exactly cheap!

There are a bunch of different things that can cause your water heater to underperform, including built up sediment at the bottom of a tank, a broken dip, or even having the actual heating portion lose its ability to do its job. A quick diagnostic can help you rule out what it could be, but

Ossiana Tepfenhart
Ossiana Tepfenhart

Ossiana Tepfenhart is an expert writer, focusing on interior design and general home tips. Writing is her life, and it's what she does best. Her interests include art and real estate investments.

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