How to isolate a baseboard heater circuit, drain, purge?

Question

I am renovating a kitchen and in the process have a need to remove a baseboard heater from a wall that will now occupy cabinets. The removal is straightforward and will take 10 minutes tops. However I of course will need to drain the line of water prior to doing so. Being from Texas, baseboard heating is new to me. I believe I have the overall concept but want to be sure so that I do not damage my system or cause future problems or hazards.

The first image is a part of the overall system. I have circled what I believe are the main components I need to worry about. Correct me if I am wrong at any point.

In pink is the power shut of for the furnace. I would need to shut this off prior to starting any work?

In green is the supply lines to the heating system (details below).

Yellow are control valves that send the water to each circuit (details below).

Blue are the return lines of each circuit (details below).

I believe that circuits 1 & 2 are fed from the supply line on the left and are controlled by the valve. The spigot allows to drain/purge the circuits. Same with circuits 3 & 4 being fed by the supply line in the middle which are also controlled with the vale and spigot.

In theory, if the unit I need to remove is on circuit 3, I'd close the valve for 3 & 4 to stop the water flow. I'd also attach a hose and bucket to that spigot to drain those lines correct? (See pink highlight).

The two main lines marked 1 & 2 and 3 & 4 in the previous image split off to individual circuits that I believe are controlled by these valves which are controlled by thermostats in the house, correct? And each of these lines go wherever they go throughout the home hitting their respective units along the way. In my example, #3 is the line my unit I need to remove is on.

After winding their way through the home all four circuits join back up and return to the boiler for reheating. Shortly after all 4 merge there is a valve that seals off water from flowing backwards into the circuits (if that's even possible?). I'm assuming that closing this valve in conjunction with the 3 & 4 valve previously mention would allow me to drain the circuit enough to do the plumbing needed. (see valve in pink below.)

Is there anything I am missing or am I completely off base here?

I am also assuming that doing this procedure introduces air into the system that would need purging.

The steps for purging would be similar I believe except I would have to have the power to the boiler on and have each thermostat running as I purge the air from each circuit?

All advise is greatly appreciated!

Answer 1

You are on the right track. Assuming you want to work on a single zone, you will need to:

1. Shut off your boiler using the switch (potentially you could disconnect just one zone and leave your boiler running for the sake of other zones, but in general it's simpler to just turn off the system unless you're doing extensive work during the winter).
2. Disconnect that zone by closing valves on both the supply and return ends of the zone's loop. It looks like you have valves on each of the zone supply lines, but only one valve on your return, after the zones are joined - the pink circle in your last pic. So you may end up draining a bit of water from other zones. Note that if you didn't have valves on both ends, you could also drain your entire system. To do that you'd want to also shut off the cold water supply into your boiler, which is always there to allow the system to fill and respond to evaporation/leaks.
3. Prepare to drain by attaching a hose/bucket to your chosen zone's drain valve/spigot. Open the drainage valve. You'll get some water out at this point, but it will be limited because there is no other opening to allow air in.
4. To facilitate draining in the areas you'll be working, open bleed valves on your radiators upstairs. The bleed valve is a smaller valve designed to let you release air from your pipes so that the there is no air in the pipes along with the water. In this case you're going to use it to allow air in instead, so that the water can drain down into your bucket instead of spilling all over your floor when you cut a pipe upstairs.
5. Make your changes upstairs. Note that if you change the layout significantly you may need to add bleed valves to facilitate purging air in the future.
6. Close all your bleed valves. Close drainage valves and remove hose/bucket.
7. Reopen all the valves you used to disconnect your chosen zone. That zone will now be filled/under pressure, but with a significant amount of air in the pipes so it won't yet be ready to run.
8. Bleed the air from the system. Note that you may need to bleed radiators in other zones as well, because it does not appear you can fully isolate the chosen zone on both the supply and return ends. When bleeding the radiators, open a valve to release air and close it when it stops sputtering. Use a cup and rag to avoid spraying water everywhere. :)
9. Check again for leaks. :)
10. Turn the system back on and test it out!

Good luck with your project!