Draining Noble combi nkc 199

Ken_Ben

Have a leak on the upper connection of the water outlet tube to the heat exchanger and need to replace the washer. (Also want to account for possibility might have to also to loosen lower connection to get tube to line up when reconnecting.) Lochinvar instructions for the water outlet tube says "drain water from unit"; but not 100 percent certain how to drain.  Based on Lochinvar and the forum (great info), these are the steps as I'm thinking (might be missing, or unnecessarily including, some). Thanks in advance for the feedback:

1) turn off power
2) turn off gas
3) shut off the "domestic cold water supply"
4) shut off the "supply" to house heating system
5) Shut off "return" valve (next to red valve)
to drain unit
7) Open red (see photo) drain(?) valve on "boiler inlet" line (Does relief valve at top of boiler have to be opened to allow air into unit for it to drain?)
8) Open (yellow tagged) valve on the "domestic hot water out" line (?)

Refilling unit:
9) Close "red" and "yellow tagged" valves 
10) Open domestic cold water to fill
11) Turn on power to unit
12) Put into service mode
13) Open relief valve at top of unit to rid of any bubbles
14) Exit service mode
15) Open house heating "supply" and "return" valves
16) Turn on gas

EdTheHeaterMan

Sounds right. I would add one more step between 13 and 14.

13.b) Open a hot water faucet in the home to purge air from DHW side of system.

Ken_Ben

Great, thanks for the feedback.