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Trouble draining boiler

JAH1010 Member Posts: 5
Hi all,

I bought this house recently and am still learning the systems. I have a 2 zone, oil-fueled hydronic heat system, and the circulator pump just broke (or, is breaking). I have a new one and am ready to install it. My plan was to drain the system from the drain valve (bottom circle in image), replace the pump, fill from the main fill line (middle circle), close the valve between the fill and the upper drain valve (top of picture, red handle), and bleed any air out of there until clean water comes out.

Unfortunately, I never quite got there. I opened up the bottom drain valve and only a little water came out. I opened the top one as well, thinking there was a vacuum, and only a little more came out - about 1/3 of a gallon total, with both valves open. There aren't any other bleeder valves in the system other than the automatic one above the expansion tank, so I'm not sure what else to do. (FYI, system was at 12 psi when I started this, though it loses pressure often. That's another thread though.)

I know I have substantial air in the system, which was a problem I was hoping to solve during this process too, but I backed out of the job. I realized also that the bottom drain valve needs to be replaced (it will only turn using channel locks), and with snow in the forecast, both of these unforeseen hiccups made me close the valves, fill the boiler, and fire it up again for now.

Any thoughts on why so little water came out? I don't mind calling a plumber, but I also would give this another try in a week or two when cold weather isn't so threatening.



  • STEVEusaPA
    STEVEusaPA Member Posts: 5,318
    edited March 2019
    If you are losing pressure often you have a leak and/or not enough water in the boiler.
    You should call your heating oil company.
    Why do you think there is trouble with the circulator? What issues are you having?
    Baseboard or column radiators?
    I only see one circulator. Do you have another or do you have 2 zone valves?

    I'm guessing you're not getting enough heat and you think the circulator may be bad. A competent tech will diagnose whether the circulator is bad, bad zone valve, the control is bad, air in the system, or there isn't just enough water in the system. The tech will show you how to bleed the system to properly purge of all air.
    And you are going to need a good tech to do annual maintenance, so best to find one before you really need one.

    You save no money making a mess replacing the circulator only to find out something like your thermostat needed batteries.

    Did you confirm pressure with a separate gauge? Maybe there isn't enough water in the system. You don't want to dry fire the boiler.

    Take a few pictures a little farther back so we can see the entire near boiler piping, all controls, and the expansion tank.
    Then we can advise further..

    If there is another valve on the supply, or most likely a check valve, you can probably close both black handled valves (note how many turns for the one circled as that is a bypass and needs to be reset to where it was, most likely not fully open), open the drain at the bottom, loosen the circulator flange bolts carefully and introduce air to drain the system. Or you can lift the PRV to let in air-and you should probably change that with the system drained.
    But re-filling and purging will depend on what type of expansion tank you have and what valve is on the tank, although it looks like it will be pretty easy.
  • Intplm.
    Intplm. Member Posts: 1,336
    Do post a few more pictures as asked.
    Describe what the system is or is not doing and we can go from there.
    A pro needed at your system still may be in your future but let's see what can be done here first.
    EBEBRATT-Ed Member Posts: 10,342

    need more pictures to see what is going on.

    Take a picture of your expansion tank location.

    I noticed the make up water going into the pump suction. I don't see a PRV valve so I guess the make up water location doesn't matter. Wondering where the expansion tank is probably on the supply. MU water and expansion tank should be on the same side of the circulator but without a prv probably doesnt matter.

  • Intplm.
    Intplm. Member Posts: 1,336
    So far the make up water looks like manual feed or that could be just a fast feed for purging on start up.
  • Lance
    Lance Member Posts: 170
    If there is water in the boiler and wont drain out of boiler drain, it is clogged or defective. Try back flushing the boiler drain valve from another source. Use a hose from hose bib to boiler drain. A washing machine hose for double Female hose bib connections is good if have another nearby source like a water heater drain. This may unclog the stoppage and allow you to gravity drain, or can add utility pump to help drain it faster. If pump used must let fresh air in or could collapse an expansion tank. Consider gauge pressure reading might be false . Could try and see if the relief valve works. May need replacing if wont reclose properly. Be prepared for flow of water. I have had to temporary plug a flow when all else failed with a nipple gate valve premade to plug the opening. I once found a defect valve cast shut. Could add hose adapter to a relief valve to drain down. Then tackle the drain valve. If you have totaly isolated boiler from system, you will need to let air in at relief valve to drain boiler.
  • JAH1010
    JAH1010 Member Posts: 5
    Thanks for the feedback. I'm replacing the circulator because it's making a loud, clacking sound that can be heard throughout the house. (You can hear it here.)

    Here are two other pics of the supply side. At the top, you can see two zone valves above the expansion tank. (The tank is good, b/c I just replaced it a few months ago. Old one was full of water.)

    As for losing pressure, I've been looking and looking for a leak, but no water has made itself known. The auto vent above the scrubber is the only vent in the whole system (none at the baseboards right now), so I don't think it's enough to handle the significant air in the system - that's why I wanted to drain the whole system and refill/bleed air when replacing pump rather than just isolating the pump to change it.

    Pressure relief valve works at 30 psi, and there is not reducer valve - just the manual fill valve you see in the middle.

    My sense is that the issue of losing pressure and the bad circulator are symptoms of too much air, and in any case, I do have a reputable tech coming out this week. (I like DIY projects, but know enough not to get over my head.) So really, I just want to understand what's going on for my own sanity.

    Thanks all. Here are the other pics.

  • STEVEusaPA
    STEVEusaPA Member Posts: 5,318
    edited March 2019
    Well you're in luck...if your valves work.

    First, the air scoop and air vent are crap (and installed wrong). Don't expect them to eliminate much air. There are better options, and because you have valves, not to hard to implement.
    Also pumping away from the expansion tank and not into it would help.

    Edit: Last post contained a mistake. The circled black handled valve is a water feed shut off, not a bypass. So it should be shut off unless you are filling the system.
    Actually it should be replaced with an auto water feeder and a back flow preventer.

    Draining is easy.
    -Close black handled on supply before zone valves Probably not even necessary if zone valves are de-energized.
    -Close un-circled black handle valve on return.
    -Open boiler drain w/ hose to floor drain.
    -Loosen circulator flange bolts. If you're careful, you can probably lift the flange with a screwdriver to introduce air and allow it to drain.
    - At the same time, put a bucket under the relief valve, open relief valve, boiler should start draining out of drain (unless clogged).
    Keep in mind if your hose from the boiler drain goes up into a sink, it wont drain, just out the relief until the level gets below the relief valve opening.

    --Properly change circulator--

    Refill/purge-Boiler off, no power to zone valves (could be a separate power supply to transformer).

    Like I said earlier, couldn't hurt to change the relief valve.
    If your gauge works, close boiler drain, fill to 20 psi.
    Put a hose on the hose bib up on the return-circled, red handle valve.
    I usually run the hose to a 5 gallon bucket, in the sink, and secure hose to bucket.
    Open black handle valve on supply. Open one zone by depressing the manual level on the zone valve.

    Now for the fun, you have to do 4 things at the same time, so maybe a helper.
    While keeping about 20 psi, watching the gauge, you have to open the fill valve (circled black handle) and open the valve where the hose is connected.
    This will send water into the return line (but blocked by the closed non-circled black handled valve, into the boiler, all the way thru the supply and open zone and out the purge valve, thru the hose and into the bucket. Keep the water flowing until you see no air bubbles in the bucket. Then simultaneously close both valves, maintaining pressure. You have to keep the pressure up around 20 psi thru the entire process.
    Then manually close the zone valve and manually open the other zone valve.
    Now repeat the process for the other zone.
    I usually rotate and do each zone twice.

    Manually close the other zone valve. Drain a little water out of the system to get the pressure down to 12 psi.

    VERY the un-circled black handled valve on the return line. That valve should be open, the valve on the supply before the zone valves should already be open.

    Now you can initiate a call for heat.
    If it were me, I would run the boiler up to temperature with both zones calling, then shut it down and purge again.


    Now if you were pumping away and had a quality air eliminator, you would never have an air problem again.
    So with the valves you have in place, it wouldn't be that hard to fix your near boiler piping.
    Then all you would have to do is re-fill the boiler and not have to purge zones.
  • Intplm.
    Intplm. Member Posts: 1,336
    Yup! That clatter sure sounds like the circ.

    Do yo have new flange gaskets and bolts at the the ready?
    You know to shut off the power and water supply to the boiler?

    The reason you cannot drain might be because , as you said, it is caught in a vacuum, or the boiler drain below the circ. Is clogged, or both.

    Open the boiler drain and lift the relief valve handle. If water flows out, then you have discovered why it would not drain.

    While you are doing this, you might want to change the relief valve too. They tend to malfunction and drip after doing this.
    If the boiler drain is clogged clear the clog and replace the boiler drain.
  • Intplm.
    Intplm. Member Posts: 1,336
    Another will need to purge the system after all this.
    To keep as much water in the system ( not the boiler ) as possible, close the isolation valves on the supply and return. They are the black handle gate valves . One is below the zone valves the other is above the circulator. This will make getting the boiler and system back up and running much easier.
  • JAH1010
    JAH1010 Member Posts: 5
    Very helpful thread, thank you all for for the insight!
  • SuperTech
    SuperTech Member Posts: 1,691
    I strongly recommend following Steve's advice and move the location of the circulator so you are pumping away from the expansion tank. Adding a pressure reducing fill valve and backflow preventer is also a must. Replace the old air scoop and vent (it is not a scrubber) with a microbubble resorber such as a spirovent or Caleffi Discal. And the fill valve should be piped into the same point as the expansion tank and air separator. I can promise you that if you do these upgrades you will never have a air problem again.
    Also I have noticed that pumping into the expansion tank drastically reduces the lifespan, that's likely why your last one failed.
  • Intplm.
    Intplm. Member Posts: 1,336
    The things @SuperTech and @Steveusa PA say above is the best thing for your system. Pending on your DIY skills you will probably need a pro to do them.
    I'd say. A little more then just changing the circ. from when you first started. Either way. Hope this has helped.
  • JAH1010
    JAH1010 Member Posts: 5
    Helped a lot, thanks. I have a pro coming out tomorrow or the next day or so at least.

    One final question - if I replace the air-scoop/vent with the microbubble resorber as mentioned above, will there be any need to add any vents anywhere else? I was thinking of adding some at the baseboards (there are no other vents in the system right now), but if I didn't have to do that, that'd be awesome.

    Thanks again, I'm quite glad I found this forum!
  • SuperTech
    SuperTech Member Posts: 1,691
    No need for any vents at the baseboards. One on top of the boiler if the manufacturer calls for it and the microbubble resorber is adequate. Once the boiler is filled and purged and you let it run for a while all the air will be eliminated. The only time you will have more air in the system is if you need to add more water to system after a repair. That's a good reason to have ball valves to isolate the boiler from the zones, it limits how much is needed to be drained when replacing components.
    Speaking of which, it's always a good idea to add valves to isolate any part that may fail, expansion tank, air vents, circulator pump, ect. You will thank yourself later.
  • JAH1010
    JAH1010 Member Posts: 5
    Just an update - new circulator is installed, system is purged and flushed and running with no air for the first time since we bought the house a year ago. Many thanks! Going to address some of the other upgrades (Autofill valve, resorber, etc.) in the offseason when it's not 25 degrees out.
  • SuperTech
    SuperTech Member Posts: 1,691
    Good job! Post some pictures here of the boiler after you get the upgrades done, I love seeing pictures of boiler improvements. I'm glad it's working now.