Hot / Lukewarm Water from Cold Tap – Common Reasons & Fixes!

Updated: | Author: Brad Javernick | Affiliate links may be present.

Having hot or lukewarm water coming out of your cold tap can be concerning. However, it’s actually a relatively common problem in households with certain plumbing arrangements. It’s also not difficult to resolve this problem with your own resources in some cases.

If hot or warm water is coming out of your cold tap, this could be caused by leaking or poorly insulated pipes. Recirculating plumbing can also cause problems with hot and cold water. Finally, pressure problems can affect the balance of hot and cold water in the plumbing, pushing water into the wrong pipes.

Inadequate Insulation of Cold Pipes

If your cold pipes are poorly insulated, they might warm up simply due to the residual heat of the ground they’re running through. If some sections of your plumbing are exposed, they might get heated by sunlight as well.

It’s also possible that your cold pipes are too close to a heat source. If you have a boiler or heating system, that could be the cause.

Note that the heating unit doesn’t necessarily have to be connected to your plumbing. Simply having your pipes running too close to it can cause them to absorb enough residual heat to warm up the water inside.

Copper piping is particularly prone to this. Copper is a great heat conductor, which means that copper pipes are going to absorb more heat from their surroundings.

Malfunctioning Thermostat

If you have a thermostat regulating the hot and cold water distribution in your plumbing, it may be malfunctioning. If the thermostat transmits an incorrect temperature reading to connected devices, this could lead to an excessive build-up of hot water in your cold pipes, or vice versa.

A malfunctioning thermostat can be difficult to diagnose on your own. It’s usually part of a larger system that you might have to shut off completely.

It’s also possible that you have several thermostats at different points in your plumbing installation. You will have to check each one separately, which requires more experience if you need to shut off different parts of the plumbing separately.

Failing Mixer Tap Valve

If you have a mixer tap valve, it may be on its way out. If you know where the valve is, you can easily verify if that’s the case by simply touching it. If the valve is hot without having been used recently, that’s very likely the culprit.

Sometimes, tightening the valve might be enough to fix the problem. In other cases, you might need to replace the internal cartridge but not the entire valve.

That’s not always the case, though. It’s possible that the whole valve may need to be swapped out. This is best done with the help of a professional. Depending on the layout of your plumbing, it might be far from a simple DIY fix.

Running your cold water tap for a couple of minutes can sometimes be a temporary workaround for this problem. You should keep it running just enough to clear out the accumulated warm water from the pipes.

However, this is obviously not a long-term solution. You should hire a plumber to replace the valve as soon as possible.

Recirculating Plumbing

Recirculating plumbing can occasionally cause these types of problems. This is not something that can really be fixed, though.

The best you can do is to keep the tap open long enough to allow warm water to reach the regulation valve. Once that happens, things should get back to normal and you should have cold water coming out of the cold tap as it should.

That shouldn’t take long in most cases. If it takes more than a few seconds, this could indicate more serious problems with your plumbing. Refer to the points above, checking any valves and thermostats involved in the system.

Pressure Problems

Pressure problems can cause all kinds of unpredictable behavior in your plumbing. This includes hot water coming out of your cold tap. The opposite is also possible.

Generally, this is because water is pushed into the wrong pipes due to inadequate pressure. This is a broad range of problems that can be difficult to diagnose by a layperson. If you suspect that pressure might be the root cause of your problems, working with a professional is important.

Depending on how your home’s plumbing is structured, you might be able to shut off the affected section without impacting the rest of the household. This isn’t always possible though, especially in smaller houses or apartments.


Leaks are another general class of problems that can lead to strange plumbing issues. Hot water could be leaking into your cold pipes, for example.

Alternatively, a leak in either your hot or cold pipes could be causing a pressure imbalance. Sometimes a small leak can be enough to cause major problems in this regard. This can make these problems challenging for the average person.

There are various signs that could indicate potential problems with the pressure of your plumbing. For example, occasionally having air come out of the tap for a few seconds. You might notice strange vibrations or even violent shaking in your tap if water is delivered in irregular waves.

Pressure problems tend to get worse over time. Whatever the original root cause is, it will not fix itself and will likely cause even more issues if left unaddressed. A small crack can eventually propagate through an entire section of the affected pipe, for example.


If you have a leak, pressure problems, a failing valve, or a malfunctioning thermostat, these can all lead to warm water coming out of your cold tap. In some cases, there might be a simple workaround that you can use until you’ve fixed the problem properly.

Whatever the actual cause is, this is always a problem that should be treated with at least some degree of urgency. Many of the issues associated with hot water coming out of your cold tap have the potential to get worse over time. This can lead to more expensive repairs.

Avatar photo

About Brad Javernick

Brad is a licensed home inspector and the editor of Home Oomph. He's a massive DIYer, and loves to take on new home renovation projects!

Leave a Comment