Draining and refilling a Burnham Boiler and Indirect Water Heater Combination

[rmcderm313]

Hi All,

I am planning on extending a baseboard forced hot water radiator in a foyer. I’m waiting for Spring in case I run into any issues, I don’t want to be without heat. I have some questions about that extension as well but I’ll save those for a later thread.

First things first, I’m hoping to get some guidance on draining my system for the repair, and then refilling it when ready. Here is a summary of my system.

Burnham Series 2 Gas Boiler
Burnham Indirect Fired Hot water heater model PAL-41 (41 Gallons)

I think I have a good handle on how it’s set up, but if I am off on anything here please correct me. Refer to the picture with the numbers on it for this description. The red vs. black number have no significance, I just used red where it would be hard to see black.

#1 is the incoming domestic water line shut-off for the boiler
#2 is the domestic (cold) water feed for the indirect water heater
#3 is a branch off the domestic water that feeds the boiler. It has a shutoff valve, and…
#4 a Watts low water pressure reducing valve, and a Watts ½” 9D-M3 dual check valve backflow preventer (as an aside, I’ve read mixed opinions on whether this shut off should be in the “on” position, but in my case it is)
#5 2 Taco circulator pumps (return side) connected to each of the 2 zones (upstairs and downstairs), each with a shutoff valve.
#6 Refers to this general area which is a loop to connect the heating coil in the indirect water heater to the boiler.
#7 Another circulator pump (supply side this time) that pulls heated water from the boiler on demand, through the loop mentioned in #6, to heat the tank water.
#8 The supply side output from the boiler. In addition to this being connected to the pump mentioned in #7 above, it feeds the baseboard radiators in the two zones. Before feeding the zones this is connected to a Taco Air Scoop with an expansion tank (see pictures).
#9 A bank of 4 hose bibs, one each for the 4 return pipes from the radiators.


I have the installation instructions from Burnham that speak to filling the system, but they don’t jive with how the system is installed in my case. First of all it doesn’t include the indirect water heater (not surprising) and the related complications that introduces. Also the circulator pumps that feed the system in the instructions are on the supply side as opposed to on the return side like they are in my installation. I believe that results in shut off valves and hose bibs being in different locations. All of that makes the instructions pretty useless.

Based on generic instructions I’ve found on draining a system, my thinking is to:

Shut off the boiler (electric switch on boiler)
Let the system cool (2 hours)
Shut off the incoming water valve at #3
Start with the hose bibs at #9, connecting a garden hose one at a time, open and drain each one (I’ll need to use a 5 gallon bucket because I don’t have a floor drain)
Open the bleeder valve on the furthest radiator to help the system flush

Here’s where I’m stuck. Should I just open every hose bib (connected to a hose of course) that I can until they stop draining? As you can see there is one right at the return side of the furnace, as well as one on the return side of the indirect heater loop. I’m just not clear on what will effectively empty the system enough to make my extension (which is on the first floor).

Then, what is the correct method for refilling once I’m done? The Burnham instructions say to use a garden hose connected to a hose bib on the supply side, which in my case doesn’t exist. Based on other reading I’ve done, I should be able to simply turn on the domestic water valve #3 and the system should fill until the low water pressure reducing valve stops it at 12 PSI (or where it’s been set).

So overall, my system has enough differences from anything I’ve been able to find online that I’m just not sure how to go about this. Any and all assistance is appreciated.

Thanks,
Rob

PS - As you’ll see in the photos if you go to the album, the PSI on the boiler is North of 12. Looks to be more like 15 PSI. Is that an issue?

 

[Dana]

You don't need to drain the whole system for this, only the part of the system that's above where you're cutting in. It looks like you have a place to drain the zones directly below the green pumps at a hose bib that you haven't numbered or labeled.

Turn off isolating gate valve between the potable & system at the auto-fill valve. Turn off the gate valve above the pump to the zone you're not working on (no need to inject air into that zone too!) Turn off the isolating gate valve to the indirect too (also not labeled.) Where ever you can, isolate, isolate, isolate, and you'll save yourself a lot of joyless air-purging later!

You also don't have to drain it completely down, only low enough to where it's below the pipes you're working on. With most of the system reasonably isolated, try drawing just a gallon or so. Any high-volume rads on the system, or is it all baseboard? With 3/4" copper fin-tube & distribution plumbing you get about a gallon out of every 50', with half inch every 100'. Since the drain tap is below the top of the boiler it would keep running until at least part of the boiler's volume has been drawn down too, which is completely unnecessary.

A system pressure of 15 psi isn't usually necessary for 1-2 story houses, but it's not a problem. Sometimes people will raise the pressure a few psi to quiet cavitation on the pumps, if they're talking a bit. (Cavitation shortens the life of pump impellers.) If the expansion tank is located reasonably near the intake sides of the pumps, raising the pressure isn't usually necessary. I don't see where expansion tank is relative to the rest of it in any of the pictures, but it's probably not a real problem.

 

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[rmcderm313]

Thanks so much! This is great...

I have all baseboard units so I shouldn't need to drain too much. Is there a good way to test whether I've drained the target pipes well enough or is it just a matter of trying to de-solder the pipe and seeing if it works?

My expansion tank which is connected to a Taco Air scoop is on the supply side of the boiler, which is counter to the Burnham installation instructions, but is recommended in the Taco installation instructions (go figure). It is very near the boiler, just after a bend to horizontal along the ceiling, within a few feet of piping. Judging by the way you asked the question about it's location maybe that's why they set the PSI high (due to it's longer distance from the return side circulator intakes).

Here is a picture of the expansion tank in relation to the boiler (lower left)..

http://s1252.photobucket.com/user/r...A-49E9-A024-093E953B7632_zpsulyupk40.jpg.html

When I go to fill the system again, how should I go about it? My potable water make up (PRV and backflow preventer) is on the return side and as far as I can tell there aren't any valves or hose bibs to open on the supply side (near the boiler) that would facilitate the water traversing from return side to supply side to fill the empty spaces in the system. Will opening the purge valves on my baseboard units be enough to let the water start flowing through the whole system? The Burnham instruction manual refers to a hose bib on the supply side that doesn't exist in my installation. Or maybe just the lack of PSI in the closed system will allow the whole thing to fill????

Your response was incredibly helpful.. Thanks for your assistance!
Rob

 

[Dana]

For re-filling, open the just air bleeder on the far end of the zone you modified, then open up the gate valve to the auto-feed you should hear it filling the system, pushing air (and eventually water) out the bleeder valve. Set it up to catch the splatter at the bleeder valve end (towels, bowls) at the ready to close the bleeder once the sputtering stops and becomes a clear stream of water. Run at least a few quarts of clear water to be sure you've gotten most of the air.

Unless you over-drained the system or failed to isolate the other zones, 9 times out of 10 that will be enough. Even though there is still some air in the system it won't be enough to halt flow, and the air scoop & vent will eventually take care of it.