Last spring I noticed the relief valve was lifting on my furnace. Its a Burnham forced hot water system. I placed a bucket under it as spring was near. Now that the cold weather has returned, I replaced the valve with a new one. Unfortunately the result is the same, meaning there is something else wrong with the system causing overpresurization and the valve is doing its job. Any ideas as to what the problem could be, and how much it will cost to repair?