Replacing an old boiler with a modern condensing boiler is not always a simple device swap. There are differences in the flue, condensate, and operating settings.
Flue
The new boiler may require a different flue gas exhaust system compatible with lower temperatures and the presence of condensate.
Condensate drainage
A safe drainage system must be provided for the water produced during operation.
Hydraulic temperatures
Condensation performs best when the return temperature is low. For this reason, a different installation setup may be required.
Combustion and adjustment
The new device must be adjusted according to the manufacturer's instructions, and a flue gas test must be performed.
Existing piping
The existing gas piping must be checked to see if it can support the new device without excessive pressure drop.