What can Cause Low Hot Water Pressure and How to Repair It?

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Having low hot water pressure at home can be frustrating and problematic. Whether it is because you can't bath as your tankless didn't turn on or because washing dishes becomes a headache, having reduced pressure is simply something you want to avoid.

But as there are many reasons for the pressure drop, there are also many ways to fix it. No matter the reason, there's always a way to get back the proper water pressure to your shower or sink. So, if you want to learn more about having the right hot water pressure to at home, the many problems you can face, and how to fix each one – then come further and find out!

Things to consider when dealing with the low hot water pressure

What is the correct water pressure?

Before we investigate what can cause low hot water pressure lets first see what is the correct pressure.

Water pressure is measured in PSI (Pound-Force per Square Inch). This measurement varies depending on the type of the water source (sink, shower, garden hose, water softener, etc.), the time of day (water pressure is usually higher at night and dawn), and the number of water sources at home.

But technically, water pressure in your home should be between 40 and 80 PSI.

Anything below 40 means that something is happening at home, and it could be one of many things happening at once.

And this is the topic of the article; low hot water pressure.

What can cause low hot water pressure?

Problems with water pressure can be as simple as just a broken pipe, or as challenging as a water heater, or worse, the leak. But being difficult does not mean that it is impossible to fix. Here we go over the different reasons why water pressure at home can be deficient, as well as some quick fixes to each:

Can a faulty water heater cause low hot water pressure?

Is your hot water heater losing pressure? Do you have a water heater connected to the source? It probably means the device is working deficiently. Any unit having this either means it leaks, the pipes are clogged, or the heater's pump is not doing its work (if installed).

Or there might be the limescale buildup, or sludge at the bottom of water tank heater and inside the water pipes. That is why it is recommended to drain and flush a water heater at least once a year. The narrow passages between the fins of the tankless heat exchanger are especially delicate and prone to clogs affecting the heat transfer.

If the water heater is equipped with heat traps (to improve efficiency), you might hear the humming noise and experience low water pressure due to the restrictions in the water flow. Also, check out any limitations in water inlet and outlet flow or water valves not fully open.

While this can be an easy job for an expert to revise, we recommend testing the device and making sure it is the heater having that problem. Then, if you don't feel confident enough looking for the exact cause, call for an expert to take a look at the heater and maybe even fix it for you.

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Can a clogged hot water heater cause low water pressure?

Sediment buildup and low pressure are pretty common as well, especially in the area with hard water. This happens mostly to aerators and showerheads, but it can happen practically anywhere, including pipes or water heater elements.

It means the minerals, dirt, and overall contaminants from the water clogged the elements in a water heating system, resulting in reduced water flow and low water pressure.

To fix the problem, make sure to have the water line completely closed, or just the one that goes to the shower, faucet, or pipe you want to clean. Then pour the solvent into the water heating system to flush all the mineral deposits. This will slowly get rid of the sediment and clear out the system.

For aerators and showerheads, you can use a brush to clear out the residue. Leaving the parts on vinegar overnight will also eliminate the hardest debris to clean inside the components.

Eventually, you'll have a clean and buildup-free showerhead, aerator, or pipe that will not reduce water pressure.

Defective pressure reducing valve (PRV)

If you find that the pressure problem is in every faucet, shower, hose, etc., in your house, very likely the problem comes from the PRV (Pressure Reducing Valve).

The PRV is almost always located between the outside water line and the house water connection. Just look at it and make sure it has the pressure screw in the right direction and level. If it does not, turn it clockwise to the right level. If this doesn't fix the problem, it is probably broken.

A PRV valve can be fixed most of the time, so you'll have to replace it directly. To do it, we recommend hiring an expert on the matter. As the PRV is connected with the outside water line and the house, it is better to call a professional.

Issues with the water shutoff valve

This valve is also close to the PRV and the connection between the house and outside line. If it is closed by mistake or bumped, it could eventually reduce water pressure. To check it, you need to turn it counterclockwise and finally test the faucets that were having low pressure before. If the pressure is fixed now, it means the problem was there. If it didn't fix, it means the problem is elsewhere.

Corroded and leaky pipes

After testing each of the previous parts, and none is culpable for the weak pressure, it may also be a leaking or corroded pipe(s). But to make sure this is the problem with low-pressure water, you'll have to check the piping system. Corrosion is often found on plumbing pipes of older homes.

Here, we recommend investigating all the areas with plumbing connections, from behind toilets to behind faucets, garden hoses, kitchen sinks, showerheads, tanks, water heaters, and so on. Ensure you check each of these, especially the connections between the wall pipes and the objects.

Another thing you can do is to check the leak indicator and the service meter. They are a great way to find out if something is leaking inside your house. The service meter usually shows leaks by adding numbers to the flow when there aren't water sources open. And the leak indicator, in contrast, shows significant leaks with a gauge but does not show the smallest ones.

If you didn't find any issue on the first try, you can come back later and recheck both. If you see different numbers even though there weren't water sources being used – it means you leak.

Apart from checking the pipes that go out from the wall, check the floor and other objects around. If any of these is wet or with excessive moisture, it probably means there's a leak somewhere. Wet marks on the walls are also a great sign that there's a leaking pipe around.

After you've found the water leak, it is time to fix the pipe. You can do it yourself by looking for a pipe or replacement of the same size as the damaged one. But first, you'll have to close the water line from outside, so no water comes in while you do it. Also, make sure to buy pipe connections so you can mount a replacement quickly.

Anyone can do this with basic plumbing levels, but sometimes it can be challenging, especially when connected to a water heater or similar product. For that, it is recommended to call an experienced plumber instead. They will save you time and effort and very likely fix your pipe problems once and for all.

Other reasons of the low water pressure

Home elevation. If your home is located at a higher altitude, you might receive water with lower pressure.

Low pressure from the main supply. The best is to call a utility company to check why you are receiving low water flow/pressure due to ongoing service.

Peak time. During the peak times, in the morning before work or in the evening before the bed, or if there is a great usage when neighbors are watering the lawn, you might experience lower pressure in the shower than usual.

Water softener issues. After many months of work, water softeners can collect all kinds of dirt and debris, making it hard for water to pass through. It is recommended to switch the water softener to bypass mode and recheck the pressure.

Low-flow faucet or showerhead. If low pressure is due to the low-flow showerhead, for example, and your tankless water heater cannot get the required water flow, change the showerhead to a newer model.

How to check (test) the water pressure

Testing the water pressure is vital as it might indicate not only low but high pressure too. Problems with low pressure are described in the above text, but high pressure is even worse. It can harm your plumbing and devices that use water, such as; water heaters and water softeners.

The testing should be done to confirm the problem and see if it is working correctly. Here's how to do it:

Using a water pressure gauge

To check the pressure, you'll need a pressure gauge kit. You can find one of these in practically any plumbing section at a hardware store; they are very affordable and can be used efficiently. After having one, you'll have to:

Go to a water outlet such as a faucet, hose, or sink in the house. The closer this outlet is to the water meter coming from the outside water line, the better it will be.
Make sure all the other water outlets in the house are closed before testing. If there's any water moving in the pipes, the pressure read won't be accurate.
Now attach the gauge to the outlet you want to check with. Use a washing machine connection and a pipe wrench to tighten it up.
After having the gauge tightly attached to the water outlet, you can now open the supply and let the water flow into the gauge.
The gauge will give you a pressure read; it will be accurate once the needle on the gauge stops moving. If it stops at 60 PSI, then that's the pressure on your water outlet. Anything below 40 PSI means you have a water pressure problem.
To make sure the test was accurate, you can check later after a few minutes. Remember to check all the other house outlets and make sure they are closed. If, after re-testing, the readings are the same, it means either you have a problem with pressure (if it is below 40 PSI) or that it is okay (if it's over 40 and similar to last time). As mentioned above, you could expect a reading between 40 and 60 PSI.
If you have problems reading the pressure with a gauge and need help, you better call a professional.

Testing with a water hose

This process is more straightforward but not as accurate. It will, however, give you a somehow useful measure to know the water pressure. Here's how:

Attach a water hose to a spigot or bib. Then open the valve, letting the water go through the hose.
As soon as the water starts going through, raise the hose with the outlet pointing up. Raise it until the water stops coming out.
The elevation of the hose from the floor to the end where water comes out is the pressure in water feet.
This number will be divided by 2.31 (this is the approximate conversion of water-feet to PSI). It comes from the 144 square inches divided by the density of water at 62.4 PSF (pounds per square foot); the result is 2.31.
When you divide, let's say, the 100 inches of the water by 2.31, it will give 43.3 as a result. That would be the approximate water pressure in PSI you have at home. Anything below 40 would be too little.

You can always call an expert if the pressure still hasn't been resolved after trying to fix & test it with the previous recommendations.

Conclusion

Having low water pressure at home is a very frustrating problem.

Whether it is poor pressure in the kitchen faucet, on the garden hose, shower, or just in the bathroom sink – having less pressure than you need can make your living very annoying.

However, if you are a DIY-er with some plumbing knowledge and the right tools, the above handy tips can help you diagnose and repair your low hot water problem.

FAQ

Why my shower loses pressure when the toilet is flushed?

When a toilet flushes, it draws cold water from the home's plumbing to refill the tank, resulting in a temporary cold water pressure drop - everywhere, including your water heater and a shower.

Why my water pressure/flow in the shower is lower after installing a new showerhead?

The reason you have a reduced water pressure/flow through your shower head is that you installed a low-pressure model. Another reason is debris in your dirty plumbing system that clogged the fixture once you start using it.

I have cold water but no hot water pressure; what's happening?

If your hot water pressure is very low while the cold side is ok, you might have a problem with sediment build-up. Once you start using hot water, sediments picked from the bottom of the tank will build up inside the outgoing water heater pipes causing water to run slowly until it entirely stops. Flushing the tank and a plumbing system will help you unclog all the elements and ensure water flow is restored.

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