What is a heating system circulator pump?

In a central heating installation, the water after being heated in the boiler is transferred to the radiators with a circulator (or in a boiler or other medium) to deliver a certain amount of heat, as the company καυστήρες Μπότης explain us.

It is then transferred back to the boiler to be heated again. Hot water is lighter than cold water and therefore tends to rise upwards, towards the radiators.

The installation that works in this way is called a natural circulation installation or a gravity installation .

Today we have a natural circulation installation almost only in solar water heaters.

We apply and use central heating installations with forced water circulation. Thus we avoid a series of studies for the implementation of which large piping sections and special constructions are required.

The use of circulators is required for the operation of the accelerated traffic heating installations.

The circulator is a centrifugal type pump that moves with the help of electricity. It transfers water from the boiler to the radiators and from there back to the boiler.

Main applications of circulators

Circulators are mainly used:

  • In heating systems with hot water
  • In closed industrial fluid circulation systems
  • In hot water recirculation
  • In autonomies of central heating installation

Circulation of circulators

Circulators, depending on the way they are lubricated, are divided into:

  1. Hydro-lubricants
  2. Oilseeds

Today, in central heating installations, we almost always use water-lubricating circulators.


Each pump consists of the impeller where the impeller is, the electric motor that ensures the rotation of the impeller, the housing where the impeller moves and the electrical connection box.

In water-lubricating circulators, all rotating parts are wetted by the water circulating inside them.

The water lubricates and cools the circulator. The advantages of the hydraulic circulators are their quiet operation, their simple construction and they do not need maintenance.

Also due to the low resistance they do not create an obstacle to the natural circulation of water if they break down.

Thus the installation can operate with natural circulation until the circulator is repaired. The lubricating circulators operate with clean water.

Dirty water can damage the circulator (usually the impeller clogs and the electric motor is damaged).


The pump must be installed when all welding work is completed and after rinsing the installation. In an accessible location, for inspection or repair, if and when needed.

So that, in case of leaks, water does not drip on the electrical connection box. With its axis in a horizontal position because otherwise we will have air retention at the highest point, resulting in poor lubrication at this point.

So that the arrow in its shell, shows the same direction of flow of water from the boiler to the radiators. So that the box of electrical connections is not down because during its venting water can get into it.

It is necessary and must:

  • Valves should be installed before and after the circulator so that in a future necessary repair or replacement, we do not have to empty the entire installation.
  • Only insulate the pump housing and not the motor.
  • In installations with the expansion tank open and the pump placed in the supply, the safety (or expansion) pipe must be connected before the pump (between the pump and the boiler) and with the suction port as close as possible to the filling of the expansion tank.
  • In systems with a closed expansion tank, the tank must be located on the suction side of the pump.
  • Do not connect the connecting cable to the piping housing or motor of the pump.

General installation instructions

The circulator can be installed at any point of the installation as long as it is placed on the center line of either the water supply to the bodies or the center return line. However, it has been established to be placed inside the boiler room so that it can be controlled better.

The installation of the pump in the supply has the advantage that the whole installation is under pressure and the suction of air from possible points that are not watertight is excluded (eg Ventilators).

The pump is placed in the return pipe, only in heating installations where the water temperature can not be controlled such as e.g. fireplaces and wood boilers.

It can also be placed in the return pipe and in installations with open expansion vessels. It should not be placed too close to the chimney and in areas with an ambient temperature above 40 ° C as damage to the circulator electrical box may occur.

Circulators should never be fitted to horizontal piping, which then descends lower than the circulator, unless this horizontal pipe is automatically vented.

Otherwise, air is collected at this point which, not only does not allow the installation to work properly but can also damage the circulator.

If we have systems with thermostatic valves in the radiators or installations with autonomous valves then, a by-pass (branch, bypass) must be placed between the supply pipe and return with differential pressure valve.

In installations with plastic or copper pipes, it is advisable to fasten the circulator to a base with rubber supports, to avoid the transmission of vibrations to the pipes.

The connection of the circulators to the piping is done, depending on their size, with fittings or flanges.

At the connection of the pump it is good to place two pressure gauges, one before and one after it. In this way the overpressure created by its operation can be measured.

Also, a thermometer in the supply pipe and one in the return pipe will allow us to control the temperature difference between the supply and return water and thus properly adjust the circulator speeds, achieving a temperature difference of about 20 ° C.

In large installations, the installation of a water filter (which can be easily cleaned) in the pump suction provides great protection.

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