FYI... I am a homeowner and not technical. Problem.. about 2 months ago my baseboard heating (hot water) starting making loud noises when the furnace turned on. It continues for a good period of time, its so loud it wakes me up. If I go to the thermostat and lower the temp the noises immediately stop. The noises come from more than 1 baseboard. I had service come to check the issue and I was told that the pipes are hitting something and need to pinpoint and eliminate where hitting. The system has been in place for years and this never occurred. I would appreciate any feedback before I call for another service appt. Thanks
It sounds like there's water in your system. When you have a hot-water based radiator system, sometimes air will get in there and start making banging noises.
If it is a water boiler, I also highly suggest getting a new tech.
When I bleed (let the air out) of my radiators, I turn the system on and let it run at a hot temp, then turn it down and let it cool off. Starting at the radiator closest to the boiler I turn the bleed valve and let all the air out until water starts to come out. It helps to have a bowl or something to catch water when it comes out.
Repeat this process until you make it to the top floor. You may have to repeat the process again in a day or so, but this should take care of the issue.
If you need a more detailed guide read here