An expansion vessel acts as a “shock absorber” for the water circuit of your heating installation. Why? Quite simply because this heated water would explode the pipes of the circuit; the expansion vessel absorbs excess pressure and variations in water volume to prevent this. But how to change it if it is defective? Follow the tutorial from belimo valves.

Defective Expansion Vessel: How Do You Know?

You can detect if your expansion tank is no longer functioning thanks properly to a few warning signs:

  • You notice that the filling of your installation is carried out very quickly.
  • You have a water leak under your boiler.
  • It often enters safety due to lack or excess water.

If all these signs are true, first check if your expansion tank is not out of adjustment. To do this, turn it off and empty all the water present in the circuit to drop the pressure to zero. Locate the valve (often located on the front of your expansion tank).

Take a pump with a barometer (which may be a bicycle pump) and inflate until you reach the right pressure, usually around 0.8 bars. Remove the pump and then restore pressure in the water circuit (approximately 1.5 bars).

Do problems persist despite this manipulation? It is therefore high time to replace your expansion tank and therefore to move on to the next step.

Change Your Expansion Tank

First of all, switch off your boiler and drain the heating water circuit. Then, once the pressure inside has dropped and the pressure gauge is at zero, unscrew your faulty expansion tank.

Seal the new expansion vessel with gasket paste and tow and take care that there is no more air!

Once this is done, we recommend that you install a quick release connector on the stem. Indeed, if in a few years, your expansion tank is again defective, this will prevent you from having to drain your boiler before replacing it.

Screw the new vase directly onto the stem and, with a wrench, tighten the lock nut. Then turn on the water supply to the boiler, increase the pressure to 1.5 bar and shut off the supply again. Check that there are no leaks and you’re done!

Defective Expansion Vessel: The Risks

In addition to causing a drop in pressure in your heating circuit, a faulty expansion vessel may form sludge deposits and thus impair the operation of your boiler. If this is not a problem in summer, in winter, that’s a whole different story. It is therefore essential not to neglect its maintenance.

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