Changing a circulation pump oil boiler

I'm not a plumber but until the professionals on here come along ..... Some plumbers suppliers will be open between now and Saturday, buying on line could take a week to deliver due to holidays & backlog. You can get pumps from €60.00 up but the cheaper ones may lack the power required in your specific case, the expensive one was fitted for a reason and it lasted 20 years ! Fit like for like and forget about it for another 20 years. Try turning the isolating valves with a flat screwdirver, adding some heat with a blow lamp may help, chances are they are seized so you may have to drain the whole system which is a pig of a job especially in mid winter. Pipe freezing kits are available - you basically temporarly freeze the pipes both sides of pump while you fit the replacement.