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Tankless Boiler works but no heat - Open system in attic/loft

Have a cabin with a Takagi T-K4 running on propane set to 167deg. I installed the system summer of 2016.
It's an open system an it feeds DHW and baseboard heat. Have a (4) port distribution manifold with zone valves to 3/4" pex lines feeding baseboard. Grundfos Alpha 15-55SF pump. 84' total baseboard + kickspace heater in kitchen. 2 story house with tankless in "attic/loft" above 2nd floor master bedroom. System runs at 30 psi. Whole system is Stainless/Copper/Brass since it is potable water.

Zone A - First Floor
1) 25' baseboard
2) 24' + Kickspace heater
Zone B
1) 18' Baseboard
2) 17' Baseboard

Worked fine last year, always slow to heat up put worked. Now this season it's having problems. When hot water is being used regularly (occupants) the heat works fine too but if ppl leave for the day the heat stops. Thermostats are calling for heat, Taco zone controller shows the calls and have the zone valves open. Pump is running. Highest flow I'm ever getting through the system is 0.5-.8 GPM as read by the Takagi controller and verified by mechanical flow meters on manifold (0.4 GPM max per Zone).

To try and fix the system I changed out pump to more powerful (Armstrong ASTRO 250SS 1/6HP). That made a little difference 0.8-1.0 GPM total but not alot. I added two more air vents to make sure there wasn't bubbles but still not working consistently. Works fine for an hour or two. I leave and check the wifi thermostat a couple hours later and its cold.

Any suggestions / ideas. Still don't understand why I get such low flows. Is it because I'm fighting gravity, pumping hot water down? I've heard of ppl with boilers in attics and they seem to work fine.


  • SnowmeltSnowmelt Member Posts: 1,195
    did you clean the little filter on bottom of cold water inlet ? lets see a picture of your set up. What was the flow last year. it may have crap on the flow control where if you take it out and rinse it off it will flow better.
  • SnowmeltSnowmelt Member Posts: 1,195
    also in a perfect situation you want a minimum of 1 inch on manifold , maybe 1 1/4 if you can. I am not sure of the Armstrong pump, but you need either a bronze grundfus 26-99 or a S. S. Taco 009 or 0011. that machine has 25 feet of head just to start with.
  • macgyver681macgyver681 Member Posts: 9
    Under Takagi
    I have all 3/4" lines, manifold is 1-1/2" square
  • macgyver681macgyver681 Member Posts: 9
    Just pulled that filter and it was pretty clogged. I'm waiting for zone valves to open now to see how it flows with that filter cleaned. Thanks, forgot that filter existed, it's well below eye level in this cramped space.
  • macgyver681macgyver681 Member Posts: 9
    Dealing with air in the system now, trying to get it purged.
  • macgyver681macgyver681 Member Posts: 9
    Ok now running at 2.6 GPM... Slightly better ;)

    Damn filter
  • macgyver681macgyver681 Member Posts: 9
    Down to 1.8GPM now.
    Didn't realize the tankless creates that much head tho. I probably shouldn't have the circulator going thru the tankless. Maybe I can do primary/secondary loop and add a separate boiler pump. Not sure how with the dhw feeding off it to tho, I'll have to think about that more.
  • ZmanZman Member Posts: 5,873
    The tankless is designed for domestic water and the high pressure drop that you can get away with in a high pressure system.
    This is one of many reasons why open heat systems are a bad idea.
    If you are going to do primary/secondary, do one better and put in a heat exchanger
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • SnowmeltSnowmelt Member Posts: 1,195
    if you go to radiant there are good diagrams to go by , you most likey need an air separator, I recommend the taco 4900. nobody is found of using the tankless for both domestic and space heat. if you buy an indirect water heater and ad another zone then you will be better off.
    also get the pumps I suggested.
    myself, I have a tk 3doing a snow melt in my moms drive way.
  • macgyver681macgyver681 Member Posts: 9
    I ended up getting a fairly new Indirect off a guy on CL that never installed it for $75. I tore out half the piping, repiped it primary secondary with Zone 3 priority for the indirect HWH. Once I did that I have the Grundfos Alpha running the Primary loop and a Taco 3 spd running the baseboard circulation. I'm getting 3 GPM on the primary loop thru the Takagi and 1.0 GPM thru each of the (4) heating loops thru the baseboard. I'm going to return the SS Armstrong and get a cheaper cast circulator for the DHW loop. Working 100% better now.
    Original system was installed in the midst of a major reno of the whole house and just didn't have the $$ and enough knowledge at the time to do it right. I like this new system much better. Thanks for the suggestions!
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