Can I use the Grundfos circulating pump to replace the faulty one in my boiler?
It is not a good idea to asume anything about the pump in a boiler.
Whilst the pump in your Combi or system boiler may have "Grundfos" on it, Grundfos make boiler specific pumps for the major boiler manufacturers.
They do this so that they can fit into the casing as they have been designed.
If you consult the boiler manual it will have a parts list in it, which will help you identify the correct pump.