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

Circulating water not getting up to temp.

stratostrato Member Posts: 3
I need some advice. I have a RFH system with two zones. Last year here in WI it got cold. Really cold. And my system seemed to not be able to keep up. The house would only get to 62-65F. When it's 30F outside, the house stays a cozy 70F. I noticed the the circulating water was only 90F (it should be 110-120F), which led me to a mixing valve that turned out to be calcified stuck in place. So I had the valve replaced in the summer. Forward to this winter, here we are in the negative temperatures again, and my house is 65F. I turned up the replaced mixing valve a 1/2 turn, hoping to increase the water temp in the loop. The temp, however, seems to hover at 95-100F. I've monitored the circulating temp for hours, and it never get's above 100F.

I'm concerned for a few reasons:
1. The house isn't the temp it should be, 70F.
2. The RFH system, the pumps, are running constantly, for days trying to reach the set temp of 70F.
3. I don't want to keep having to adjust the mixing valve for when it's cool or really cold out.

Any suggestions?


  • ZmanZman Member Posts: 6,301
    Is your tubing in concrete?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • stratostrato Member Posts: 3
  • hot_rodhot_rod Member Posts: 14,371
    Two things needed to move heat energy, temperature and flow. Sound like either or both may be the cause of underheating.

    As far as temperature, what type and size of boiler? Does it run non-stop on cold days? How was it sized?i

    Flow issues could be too long of loops, undersized circ, piping issues such as undersized pipe, improper configuration, etc.

    Was a heat load calc performed for the home, or a radiant layout showing tube spacing, loop length, etc?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • stratostrato Member Posts: 3
    Thanks for the help so far.

    The boiler is a Bradford White combination water heater and heat exchanger. 45 gallon. The unit itself does not run non-stop on cold days, but the pumps do.

    The domestic water is very hot. Scalding, in fact, while the water heading to the in-floor loop is lukewarm.

    No idea how it was sized. It was here when I moved in 6 years ago.
  • icesailoricesailor Member Posts: 7,265
    IMO, if it is a Bradford White 45 gallon electric water heater, (I didn't know they made a 45 gallon unit) if is a direct fired unit, and if so, the raw water being heated in the tank (that calcified the mixer) has calcified the coils under the floor and insulated them from heating the space.

    You need to take some photos of what you have. The tank, mixer, the radiant manifold blocks.

    Maybe there is an indirect coil in your water heater? Street/house pressure will usually ruin radiant coils.
  • hot_rodhot_rod Member Posts: 14,371
    The original CombiCor had an output sheet for the coils. I know you will not get the full burner output into the coil HX available to the radiant.

    If it is one of the early Combicors they had a horrendous pressure drop, it was just a large coil of 5/8 aluminum coated tube. it took a high head circ to get much of any output from the coil.

    I believe the new versions have a large 1-1/2" steel coil for the hydronic loop, glass coated on the outside of course.

    The coil output is somewhat limited by the fact it is in still water, not ideal for best heat transfer.

    Find out which model you have and look up the spec at Bradford White.

    Also if it has had hard water running in the tank, there is probably a good build up around the outside of the coils. You may need to dilemma the tank somehow.

    If the system once worked well, you probably have a HX problem.

    I installed a bunch of the early CombiCors, as I recall @ 40-45,000 BTU on the hydronic side was about what to expect.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • hot_rodhot_rod Member Posts: 14,371
    Here is the spec sheet on the large coil version. Note the coil outputs are based on a 180F tank temperature!
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • icesailoricesailor Member Posts: 7,265
    hot rod said:

    Here is the spec sheet on the large coil version. Note the coil outputs are based on a 180F tank temperature!

    And we ALL know how long the warranty is on steel tanks run at 180 degrees. Let alone the DHW water coming out of the tank at that temperature.

    Be sure to heat trap that mixer.

Leave a Comment

BoldItalicStrikethroughOrdered listUnordered list
Align leftAlign centerAlign rightToggle HTML viewToggle full pageToggle lights
Drop image/file


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