The plumber replaced the pump...did he replace the fan too?
He's working illegally and only registered engs. are permitted to work on boilers regardless of whether it's just a pump swap.
If you are going to drain it down to check hose/add more cleanser, disconnect and remove the isolation valves underneath (return and flow). Do not turn them off as they will leak, when the hoses are removed (or possibly pump being replaced) to clean a lot of crap falls into these valves and blocks them.
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local