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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
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.