We had issues with our boiler unit as it made a brutal grinding sound at the pump. I called Brent Air and they sent Gary out...naturally the sound stopped as soon as he got there. In any case, about a week or so later it started again and this time Gary was able to get to the house and hear what the problem was. He replaced the pump attachment and no noise since (knock on wood).
Brent Air is whom we used for our annual servicing of the furnace and they prove time and time again to be reliable and fair. Totally recommend.