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Thermostat set at 69 room stuck at 67

About 5 years ago I put radiant heat system in a small apartment I was building for my elderly parents. Heat source is Veissmann Vitodens 222. I set the thermostat for 69 and other than changing the batteries never touched it again. Monitoring the room temperature over time I found it wold range from 68 to 70 occasionally see 71. 2 months ago I noticed the apartment felt cool, in looking the thermostat I noticed it was 67, monitoring it over the course of a few weeks it ranged 66 to 67, so i bumped the thermostat to 70 and monitored it for a few more weeks I'm now seeing 67 to 68.
I called for service and described what's going on, they said they will purchase a part and be out the following week. Tech comes out and says nothing is wrong..we just need to be patient because radiant takes time...talks about outside sensor (it's winter her in NE). In the end he says he'll bump the boiler temp up a bit and I should be all set.
Been monitoring it, I now get 68 to 69 but not back to the 68-70 range I was used to seeing.
I guess what concerns me is for 3+ years of seeing 68-70, the fact that it was stuck at 67 seems to me a sign something has changed or not working as it should. Boosting the boiler temp is not addressing the root cause.
I should add that over the years I've put my hand on the manifold when the system is running and it would be hot, now it's just luke warm.
Any suggestions, am I overthinking this or did the tech miss diagnose?



  • Brewbeer
    Brewbeer Member Posts: 616
    The boiler supply temp varies with the outside temp, the colder outside, the warmer the boiler supply temp.
    Any changes is occupancy or use patterns that could explain the temp differences? If we watch a movie at my house, the temp in the family room cones up a couple degrees from the people and electronics.
    Hydronics inspired homeowner with self-designed high efficiency low temperature baseboard system and professionally installed mod-con boiler with indirect DHW. My system design thread: http://forum.heatinghelp.com/discussion/154385
    System Photo: https://us.v-cdn.net/5021738/uploads/FileUpload/79/451e1f19a1e5b345e0951fbe1ff6ca.jpg
  • Jamie Hall
    Jamie Hall Member Posts: 22,893
    Did anyone put down a new rug or something of the sort?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • JohnNY
    JohnNY Member Posts: 3,226
    edited January 2019

    I recently started using a Powerflush pumping unit I bought from Caleffi. The two radiant systems I flushed with it brought back surprisingly slushy, dirty water through the return. Mind you, these are systems I've purged of air or replaced glycol in the past through the existing pressure reducing valve. The powered pumping unit is a different thing providing 13 GPM at 60 PSI.
    I have to believe heat transfer was suffering with this soupy water quality because my temperature difference (∆T) increased significantly after I put it all back into service. Perhaps someone else has another example of this. I intend to use the Powerflush on my previous installs knowing what I know now. Perhaps you should inquire about having your system's tubing flushed through.
    Contact John "JohnNY" Cataneo, NYC Master Plumber, Lic 1784
    Consulting & Troubleshooting
    Heating in NYC or NJ.
  • PeterB62
    PeterB62 Member Posts: 2
    Thank you for the feedback and pointing out things that hadn't crossed my mind. Fact of the matter is it could be any one, or a combination of the 3 things mentioned.
    1) the apartment has been empty since August, so unlike last winter there is no activity.
    2) we installed new carpet in the fall with rubber padding, the old carpet didn't have padding.
    3) I'm on a well, and although I have a 5 micron filter I do notice a fine residue in places like the toilet bowl, makes me wonder if that residue is inside the system.

    Thanks again!
  • Jamie Hall
    Jamie Hall Member Posts: 22,893
    That rubber padding alone may be the culprit. Turn up the water temperature a bit.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England