There are some things that you should go to a pro for, this might be one of them.
However, you could take the old unit off and replace it with a new one and you should be good to go.
Which one is it? The one on the left, or the right? The one on the right looks like it is rusted in. Hit it with penetrating oil daily for a few days (weeks?) before trying to remove it. If you decide to go with a pro, then do the same for him. You don't want him breaking off the nut and having to drill it out.
First go to the auto store and buy yourself a deep socket the same size as the gland nut (what your tube goes into). Introduce it to a grinder (better yet a Dremel) and cut a slot from the end that goes onto the nut up to where the copper tube will clear the nut when the socket is put on the gland nut (take a look at an O2 socket for a car to get an idea of what I'm talking about).
Open up your boiler (after it has cooled down) and remove the switch from its bracket and disconnect any wires connected to it (remember where these go).
Carefully bring out the switch making sure not to crimp the copper *tube* (it's not a copper wire, it's a tube, and if you crimp it by bending it too tightly you will ruin it). Having an assistant hold the old unit clear and having him/her rotate it as you loosen up the nut (bolt, whatever) will keep you from ruining the tube. Getting the old one out without destroying it will be good practice for putting in the new one without ruining it.
Put in the new one, using teflon tape *only* if it is recommended (I don't see why not), otherwise use pipe dope.
Mount the new switch where the old one was and reconnect your wires.
You did take this opportunity to flush out your boiler?
However, you could take the old unit off and replace it with a new one and you should be good to go.
Which one is it? The one on the left, or the right? The one on the right looks like it is rusted in. Hit it with penetrating oil daily for a few days (weeks?) before trying to remove it. If you decide to go with a pro, then do the same for him. You don't want him breaking off the nut and having to drill it out.
First go to the auto store and buy yourself a deep socket the same size as the gland nut (what your tube goes into). Introduce it to a grinder (better yet a Dremel) and cut a slot from the end that goes onto the nut up to where the copper tube will clear the nut when the socket is put on the gland nut (take a look at an O2 socket for a car to get an idea of what I'm talking about).
Open up your boiler (after it has cooled down) and remove the switch from its bracket and disconnect any wires connected to it (remember where these go).
Carefully bring out the switch making sure not to crimp the copper *tube* (it's not a copper wire, it's a tube, and if you crimp it by bending it too tightly you will ruin it). Having an assistant hold the old unit clear and having him/her rotate it as you loosen up the nut (bolt, whatever) will keep you from ruining the tube. Getting the old one out without destroying it will be good practice for putting in the new one without ruining it.
Put in the new one, using teflon tape *only* if it is recommended (I don't see why not), otherwise use pipe dope.
Mount the new switch where the old one was and reconnect your wires.
You did take this opportunity to flush out your boiler?