Connect fitting with boiler

If you want to install a boiler under the kitchen sink or bathroom vanity, you have to connect it correctly to the tap. And it also has to be the right fitting. In the following, we will explain how to proceed with the matter and what you have to pay attention to.

The right fitting for boiler operation

If there is only one cold water supply at a tap in the domestic water system - either because there is no central hot water preparation in the house or because there is simply no hot water pipe leading to the tap in question - you have to provide hot water locally. This is usually done with a water heater or a boiler. In contrast to an instantaneous water heater, a boiler has a water reservoir in which it holds warm water for direct consumption.

Boilers are usually not pressure-resistant. This means that they cannot withstand the pressure of the domestic water supply system (between 3 and 6 bar as standard). Although there are now pressure-resistant boilers, the non-pressure-resistant (open) models still have a larger market share.

For a non-pressure-resistant boiler, you need a low-pressure fitting. This will protect the boiler from excessive pressure and from bursting. This is because a low-pressure fitting shields the boiler from the full house water pipe pressure with a separate connection hose to the cold water pipe. The cold water from the house water pipe first flows through this connection hose into the fitting, from where it flows into the boiler when hot water is drawn off at low pressure.

Connect the fitting to the boiler

Because of the necessary separate cold water connection, a low-pressure fitting not only has 2 connection hoses as with a normal high-pressure fitting, but 3:

  • Connection hose from the fitting to the house water pipe
  • Cold water inlet from the fitting to the boiler
  • Hot water drain from the boiler into the fitting

You have to connect the cold water connection hose from the fitting directly to the house water pipe. The other two hoses are for the cold water inlet from the fitting into the boiler and the hot water drain from the boiler into the fitting.

The hoses to and from the boiler are marked on most fittings with blue and red according to the cold water inlet and hot water outlet. The third, mostly unmarked hose belongs to the cold water connection of the domestic water system, so it is connected directly to the angle valve.

When using a boiler for the first time, make sure that it is vented. To do this, open the angle valve and the tap. Let the water run in the cold and warm water position until the jet no longer bubbles and scoffs. When the boiler is vented and everything is tight, you can connect it to the electricity and start up.