Burnham Alpine Gas Boiler replacing High Limit Sensor - depressurizing and repressurizing boiler?

[day123]

My Burnham has stopped producing heat so did some research and confirmed that I need to replace my High Limit Sensor. Since the system is pressurized, not entirely sure how to go about it.

I assume the steps are as follows:
1. Turn off the power to the Boiler
2. Close the water valves to isolate the Boiler? (Circled in red)
3. Drain out the water through the drain valve which will depressurize the system
4. Once that's done, you can unscrew the faulty High Limit Sensor
5. Wrap the new sensor with Teflon tape and screw it in

Then I am kind of unsure how to repressurize the boiler. Will just reopening the water valves i closed automatically refill and give the boiler the correct pressure? Any insight would be greatly appreciated!

 

[Fitter30]

Turn gas off to boiler, turn thermostats up hopefully pumps will run cool boiler down to under 100°. Turn power off to boiler and pumps, check system pressure take note of it. There are two shut off valves yellow handles shut them to isolate boiler. Crack drain valve put a hose on it if floor drain isn't close. Water will get air bound, when limit is pulled it will start sucking air, put the new one in, before it's fully tighten, close drain valve, finish tightening, open boiler valves, check for a leak, wire new sensor. Pull up on the relief valve handle see if any air comes out, turn pumps on, air bubbler should take out the air in the system, wait 20 minutes, turn pumps off check boiler pressure, looks close, turn gas on, all power, fire boiler. Might have to cycle power to boiler to reset burner control.Use pipe dope with t teflon tape if u have some.

 

[Sponsor]

 

[day123]

Thanks, looking to replace very soon!

Also, curious how you would purge this heating system.

I believe the process is as so:
1. Isolate zone valves (both the Supply circulator pumps and Return T-Purge Valves)
2. Attach the Hose to the zone of the T-Purge Valve you are looking to purge
3. Open the Supply line's circulator pump Valve of the respective zone (the one attached to the hose)
4. Turn the Return T purge valve so that it stops flow going to the boiler and unscrew the purge knob (water should then leave from the hose)
5. Then isolate it all up and repeat for every zone

Is there anything else I missed? I know the first image you were looking at is a partial part of the heating system so here is sort of a whole-look schematic:

 

[Fitter30]

Thanks, looking to replace very soon!

Also, curious how you would purge this heating system.

I believe the process is as so:
1. Isolate zone valves (both the Supply circulator pumps and Return T-Purge Valves)
2. Attach the Hose to the zone of the T-Purge Valve you are looking to purge
3. Open the Supply line's circulator pump Valve of the respective zone (the one attached to the hose)
4. Turn the Return T purge valve so that it stops flow going to the boiler and unscrew the purge knob (water should then leave from the hose)
5. Then isolate it all up and repeat for every zone

Is there anything else I missed? I know the first image you were looking at is a partial part of the heating system so here is sort of a whole-look schematic:

View attachment 103179

There won't be that much air. A 150k boiler only holds 1.3 gallon of water. Your micro bubbler air removal device will take the air out.( brass devise that the ex tank is piped to) Just run the pumps with boiler not firing for hour if possible.