the lever you are descriding is a low water cut off
the myth is you are not cleaning the boiler you are cleaning the prob or float on the low water cut off to make shure it works right
here is what you need to do
first you need to go to a plumbing supply and get what is called a " dirt pocket " drain the doiler and remove the old dirt pocket ( when you see the part you will know what it is ) try to clean the low water cut off out then install the new dirt pocket and you are done
the dirt pocket is about 12 bucks if this works you saved close to 300 to 400 only beacuse if this fails the low water cut off will have to be replaced
i feal it is verry important to do this seeing how this control is vital to equiptment safty
Plumber
plumbing and construction