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N°2 – Single return condensing boiler – Part 1 training (A to HND level)

Contrary to standard boilers and certain « low-temperature » boilers, condensing boilers do not have a lower water production temperature. It is therefore possible to ensure a set point line acting on the modulating burner. Unless the boiler also deals with DHC production, there is no need to fit a 3 way valve for outlet temperature control.

In individual heating, taking into account an interior compensation sensor, permits optimal control (see course : «Control of individual systems – Part 2».

In individual heating, when the system has 2 circuits of different temperatures, the low temperature circuit can be fitted with a basic mixing bypass.


Considering the set point line of the radiator circuit below, draw the set point line for an under-floor heating system for the above boiler:

As a change we could use the diagram below in which the mixing bypass is replaced by a decoupling cylinder.

Note: in the above the presence of a balancing valve at the primary side of the decoupling cylinder, without which the flow in the radiators would be insufficient.