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Navien 210 Heating Help

Zanegst Member Posts: 1
I finished the installation of my unit yesterday domestic hot water works great, however I am running into issues with the heating side. I purged the unit 3 times I get a delta of appx . 20 degrees from supply to return however the house is heating up VERY slow. Took 5 hours to go up 9 degrees. Started at 9 am at 56 degrees Appx 65 feet of baseboard. I have a pressure gauge on the navien primary manifold at the supple side with heat on shows 20 psi , however unit display states 31 ... why the difference ???? Temperature is set to 190 (which it doesn’t reach) I am frustrated at how long it’s taking to heat up the house. - am I missing something here ? Circulator is a taco 1/25hp on supply side, could it be that it is too weak to overcome the primary loop pump???? I am baffled as to how there’s a 20 degree delta yet it’s not warming up. Any help is appreciated.


  • SuperJ
    SuperJ Member Posts: 609
    Is the 20deg delta on the boiler or the heating loop?
    Can you post some pictures? Perhaps you have some air trapped if you just turned it on.
  • Gordy
    Gordy Member Posts: 9,546
    There is the delta on the navien (boiler side), and the delta on the system side. Which is 20?

    What is actual supply/return temps at each side?
  • mikeg2015
    mikeg2015 Member Posts: 1,194
    A single small 1/25 HP pump for the boiler and ALL loops will probably not move enough water. Bet it’s only flowing about 6gpm to take a WAG. So 60000 btu output.

    Why are you running a mod-con boiler at 190? It’s only about 86% efficient with a return water temp of 170.

    Is this NFC a combi boiler? Max heating output is only about 80k I think with a 20f delta T because the internal pump is limited in output. I think 8gpm max is all you get. DHW can get more output because delta
    T can be 40+f.

    Also the unit may limit firing rate to control exhaust temps so it doesn’t melt the pipe. If you use polypropylene on the exhaust instead of PVC you can run higher ouet temps.