Hot water flows from a cold tap: reasons


  1. main reason
  2. Improper bidet operation
  3. Incorrect boiler connection
  4. Incorrect installation of the mixer
  5. Gasket wear
  6. Mixer wear
  7. Oil seal wear
  8. Mixer factory defect
  9. Effects
  10. Problem warning

Residents of urban apartments often face minor problems with plumbing equipment. And calling masters to eliminate them is not always cost-effective. Sometimes it’s easier to find the cause on the Internet and try to eliminate it on your own. If hot water suddenly flowed from a faucet of cold water, the tenants are most likely to blame for this. This phenomenon may have several causes and solutions. Some of them will require time-consuming, and in some cases you will have to invest more money. Consider what can be done if hot water comes from a cold tap.

We understand why sometimes instead of cold water from the tap is hot

main reason

If hot water flows from a cold faucet, there may be several reasons. Hot water alone cannot get into the cold water pipe. Pipes with heated and cold water have different pressures, in the DHW channel it is greater. But due to improper connection or operation of devices, hot water under higher pressure displaces cold water from the pipe.

Unfortunately, this phenomenon affects not one apartment, but all floors with a common riser. If such a problem occurs, it is not a fact that the reason is in your apartment. We have to think with our neighbors why warm water comes from a cold tap. You can check this as follows: at the entrance to the house, close the cold water shut-off valve, then in all apartments open the cold water tap. If nothing flows, then everything is in order. Where water has flowed, you need to look for a malfunction.

If during the inspection none of the tenants has water, then the reason lies in the pipeline. It is necessary to ask the neighbors which of them have recently installed a water supply system. If this was not done correctly, pressure increases in the pipes when the pressure increases, and hot water displaces cold water.

Cold water riser of an apartment building

Improper bidet operation

A bidet is a hygienic shower. To pour water, you need to open the mixer and press the button. After completing the water procedures, press the button and close the tap. But many simply turn off the button, leaving the mixer in the open state. In this case, hot water mixes with cold water and in this form flows from taps. Neighbors can turn on cold water, then the pressure in the system drops. Consequently, hot water will displace cold water.

USEFUL INFORMATION:How to replace a cartridge in a water filter: filter maintenance, how often to change

Due to the pressure difference, hot water flows through the cold pipes. To avoid this, remember to close the bidet mixer.

When using a bidet, do not forget about some rules

Incorrect boiler connection

Due to poor installation of the water heater, this problem can also occur. If you recently installed a boiler, then you do not need to think long about why a malfunction occurred. Just check that the installation is correct - if there is no check valve, the heated water will enter the riser from the cold. Due to pressure drops, the water heater itself may break. Typically, a check valve is placed under the water tank after the shutoff valves.

It is very important to use the boiler correctly. Before use, it is necessary to close the DHW valve and unscrew the inlet and outlet valves. If the valve remains open, then the heated water will go into the cold water pipes.

To avoid overpressure in the pipes, after using the boiler, you must repeat the steps in reverse order. Close the inlet and outlet valves, and open the shut-off valve.

So that the boiler does not cause a breakdown, you should be careful when installing it

Incorrect installation of the mixer

Often residents of apartments change faucets by yourself. If this is done by an inexperienced person, he may not install the crane correctly. The whole secret is to carefully tighten the mounting washer. This is why the installation may fail, and hot water will pour instead of cold water.

If you are sure that the mixer is installed correctly, it is possible that it has deteriorated during operation. Most often this happens with old cranes installed back in the Soviet era. Over time, the following failures occur:

  • Rotting gasket.
  • The cartridge of the mixer loses its tightness.
  • Gland wears out.

Also, the cause may be a factory defect of the mixer. Unfortunately, this is not uncommon, therefore it is better to choose high-quality fittings, for which the manufacturer gives a guarantee.

USEFUL INFORMATION:Methods of attaching polypropylene pipes to the wall

An improperly installed mixer can also cause trouble.

Gasket wear

This problem occurs in most situations when hot water flows instead of cold. Rubber gaskets in mixers can serve 10 years, but according to the rules, it is worth changing them every 2-3 years.

An indicator that it is time to change the gasket is the buzz of an open tap. Over time, the rubber wrinkles and water begins to vibrate due to strong pressure. From this, an unpleasant sound appears.

You can change the gasket yourself.

  1. Shut off the water.
  2. Remove the mixer, disassemble it and remove the gasket.
  3. Replace the new rubber band.
  4. Assemble the faucet, install it and turn on the water.

If the unpleasant sounds have disappeared, and cold water comes from a cold tap, then you did everything right.

Replace the worn gasket in the mixer

Mixer wear

If replacing the gasket did not help, the mixer will have to be disassembled again. You need to check whether the gasket has been installed correctly. When you are convinced of the correctness of your actions, but hot water still comes from a cold tap, you need to completely change the mixer. In modern cranes, other parts that cannot be repaired can also wear out.

You must choose a quality device so that it does not break immediately after installation. Better to give preference more expensive options from reliable manufacturers.

Replace worn plumbing devices only with quality products.

Oil seal wear

If everything is okay with a closed tap and there is no water flowing anywhere, and when hot water is opened from under a cold valve, then you need to change the stuffing box. It could wear out from prolonged use.

Fixing this is simple enough. Here's what you need to do:

  1. The gland nut is twisted with an adjustable wrench.
  2. Tow, greased with oil or solid oil, you need to wrap the valve stem with a thin layer.
  3. After that, the nut is screwed back. This must be done carefully so that water continues to flow from the tap as usual.

USEFUL INFORMATION:Connection scheme reverse osmosis: assembly and installation

Replacing the gland in the tap is quite simple

Another option to resolve the issue is to change the seal or the entire valve.

Mixer factory defect

If you have done all the procedures described above, but instead of cold water it still goes hot, then do not exclude the factory marriage of the mixer.

Typically, the defect is a poor seal, which is inaccurate in size, or in cracks and substandard parts of the mixer. A new crane with defects can be exchanged in the store for another.


If the cause of this phenomenon is an incorrect installation of plumbing, then the residents are to blame for this. Therefore, the management company is not responsible for breakdowns caused by this problem.

Boiling water from a cold water tap is unpleasant, but there are other consequences. For example, some appliances are not designed for hot water. These include:

  • Cold water meter.
  • Toilet bowl.
  • Cold water pipes.
  • The flush mechanism of the toilet.

If these items become unusable through your fault, then the responsibility lies only with you.

In order not to suffer from unpleasant consequences, trust the installation of plumbing professionals

Problem warning

You can protect yourself from a situation when hot water flows instead of cold. To prevent pressure differences, check valves can be installed at the pipe inlets. Or you can put modern water meters, on which there are such valves.

When hot water appears in a cold water tap, there is no need to make hasty conclusions. It is much more effective to get together with neighbors and brainstorm why this could happen. If someone has recently had repairs in the bathroom, then it is advisable to look for a reason in this apartment.

In order to avoid such situations when hot water comes from a faucet with cold water, or vice versa, instead of hot water comes ice water, it is necessary to trust the installation of plumbing to professionals. Now you know what to do when such a situation arises, but it is better not to allow it at all.