Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.

If you've found help here, check back in to let us know how everything worked out.
It's a great way to thank those who helped you.
Need to contact us? Visit

can someone explain what is happening, furnace not snapping off

My new house has a domestic h/w system off an oil fired Burnam V-1, installed 1995. The hotwater heat has two systems, one radiant in the "old" part of the house, and a baseboard loop in the "new" part. During the summer, when I'm away from the house for a period of time, I turn the whole furance off (kill switch) to keep it from periodically heating the slug of faucet h/w in the internal coil.

When I return and snap the furnace back on. It usually runs for a few minutes and stops. When it gets it first call for hotwater at a tap, it will start again, and then , for some reason, starts sucking hotwater to the radiators (heat is turned off) while making a water hammer type sound. I don't think the water pump it on, but blistering hot water seems to be getting sucked up to at least the first floor. Doesn't seem to affect baseboard system. Even if I turn off the hot water faucet, the furnace seems to be "stuck" on, burning and burning despite no call from anywhere. The last two times, I turn it off again, let it sit a bit, and then it seems to work fine again. Any explanation? Anything to prevent this? (ps I miss my old steam furance so much)


  • HVACNUTHVACNUT Member Posts: 3,099
    So long story short, you're getting heat in the radiant zone whenever the boiler is on even though the heats not on?
    Can you post some pics of the boiler and connected piping?
  • steamnoobsteamnoob Member Posts: 28
    Yup. so hot water is going up the "radiator" path, but not the baseboard side (or at least not by an appreciable amount). And unless it is the quitest least vibrating water pump I've ever encounters, the water has to be flowing via suction. I do have an expansion tank above (not in picture). Pretty sure it is open.
  • HVACNUTHVACNUT Member Posts: 3,099
    Those green Taco flo checks at the baseboard and radiant arrows.
    There might be something stuck in the weight seat causing gravity flow. Not suction.
    Try loosening the wing nut on top and turn on the heat for the radiant. Let it run for a few minutes and turn the heat back off. Tighten the wing nut.
    If that doesn't do it, you'll have to replace the weight insert at least. Maybe the whole flo check.
  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 6,744
    The flowchecks as @HVACNUT mentioned is par of the problem. But you need to find out why the burner is staying on even when it is not calling for domestic hot water....sounds like a wiring or control problem.

    Take pictures of wiring and controls with the covers off. Shut the power off when removing/installing covers
  • HVACNUTHVACNUT Member Posts: 3,099
    @EBEBRATT-Ed I guess I glossed over that part.
    Oil fired.
    From what I see, I think that's a Honeywell R8182 Triple aquastat/cad cell relay combi.
    Things aren't looking good from Jump St.

    @steamnoob remove the grey cover from the control on the burner. There are three dials. Hi, Lo, and diff. What are the settings? Post back.
    That control can be set to maintain a minimum boiler temperature. So having the burner continue to run a bit after you turn off a hot water faucet is not a concern. You can turn the low all the way down.
    There are also much much much better, safer controls than the obsolete R8182. And a modern aquastat can be set up for "cold fire" which is what I think you're looking for.
  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 6,744
    Agreed Either the settings are wrong LL jacked up or defective and hitting hi limit
  • steamnoobsteamnoob Member Posts: 28

    looks like 190HI 170LO with a 15 Diff.

    I'm sort of understanding the "gravity" concept. The wing nuts on the taco units seem pretty toight. I'll try what @HVACNUT recommended later this week. As mentioned, after the inital meltdown, the system seems to be working now. This only happens when I fire the furnace after sitting for a couple days.

    I really hate the domestic hot water, even after fiddling with mixer valve, hard to maintain a constant shower temp, and hate firing up a big noisy oil furnace in the middle of summer. Was planning on just putting in a gas water heater. Any advice...

    1. If I cap the domestic hot water lines, and disconnect the thermostat wire, do I need to do anything else to the furnace.
    2. Am I crazy to go the tank route... is there something else I should consider. I do have gas service, but hear pretty negative stuff about hi efficiency tankless.
  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 6,744
    Yes, put a gas water heater in. Tankless coils are problematic.

    Cut the pipes going to the tankless coil you can leave them uncapped.

    Your boiler will still run on the low limit control in the summer so the easiest thing is to just shut the boiler off in the summer.

    The low limit control that runs your boiler in the summer can't be disconnected it's built into the control. There are ways around this which would require a few relays and some wiring if just shutting it off is a problem. You would still need to fix the Flocheck problem because you have multiple zzones
  • HVACNUTHVACNUT Member Posts: 3,099
    Dummy me just realized it's a tankless coil.
    Do the gas water heater.
    The Lo needs to be kept at about 140° to provide, hopefully decent hot water.

    Who said you had to go high efficiency tankless?
    I'm an oil guy at heart but if you want to switch, a cast iron atmospheric gas boiler, indirect water heater, stainless chimney liner and outdoor reset. Smooth sailing for 30+ years.
    Of course oil tank abatement with certificate if the tank is buried.
  • steamnoobsteamnoob Member Posts: 28
    I was thinking about doing it all in one shot with indirect water heater, but really wanted to take care of the hot water problems before really investing in an entire system upgrade. We'll see how ambitious I get this weekend. I'm just down the road a bit from the all steamed up guys, maybe I'll see if they can figure out my flowcheck prob. Thanks for all the helps folks.
  • HotanCoolHotanCool Member Posts: 53
    Letting a Boiler go cold for 6 months or more has been debatable, especially an older Boiler. It's why I like Indirects.
  • steamnoobsteamnoob Member Posts: 28
    well, I might need to go the indirect route since I have some sort of weird indirect chimney and can't figure out on the vent the dang thing.
Sign In or Register to comment.


It looks like you're new here. If you want to get involved, click one of these buttons!