Radiant in-floor heating problem

Old 09-23-04, 07:42 PM
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Radiant in-floor heating problem

I would like to get some input on an odd heating problem.
There is a quite new house (a little over 5 years old) in
seemingly good condition with a hydronic (radiant in-floor)
heating system with 6 thermostats (2 on every floor) each
controlling their own respective zone valve. Water is heated
by a gas-powered burner for both hydronic and domestic use.
The hot water goes into separate (copper) pipes leading to
the different heating zones (with a separate zone leading to
the hot water tank for domestic use). Each of these zones is
controlled by a two-position (normally closed) straight-through
valve operated by a Honeywell V8043G1018 4-wire valve head
located on the supply (i.e. hot) side in a manifold located
above the furnace. All of the end switches for these zones
are wired in parallel to the furnace and circulator pump.
While these controls and the division of the hot water into
the different zones are located in the furnace room (which
also houses the hot water tank), there are also separate
supply (incoming) and return (outgoing) manifolds located
in each zone area.

On both the bottom and the first floors, the heating is uneven:
even after turning up the thermostat for 3 hours, there are
some (isolated) spots which should be warm but are not.
For each zone, when the thermostat calls for heat, the motor
in the zone valve powerhead turns and closes the switch to
start the furnace as well as (what sounds like) the pump and
opens the valve to let the hot water through -- as it should.
Shortly afterwards, the pipe in the furnace room leading from
the valve (controlling the activated zone) and going into the
wall becomes very hot to touch. The in-flow supply manifold
(where the hot water goes before branching into the various
circuits of the area to be heated) located in that zone itself
also becomes hot, but the return (out-flow) manifold is at
most lukewarm. Is this usual?
When I tried bleeding the Taco (bleeder?) valve on the return
manifold of one of the first floor zones, colorless lukewarm
water (but no air bubbles) came out, but this bleeding did not
improve the heating. (Written on this cylindrical-shaped Taco
valve is 150 psi, 240 F, Italy, and there is a Schrader
valve-like opening which opens when it is depressed.)
The other remaining zone on the first floor and the two in the
bottom floor have no such valve and so cannot be similarly bled.
How can I eliminate the cold spots?

On one of the second floor zones, this problem is even more
pronounced: while some areas are warm, there are large swathes
(entire rooms) which are cold. Moreover, although the
controls seem to be working (in the way described above),
only one of the three pipes leading out from the supply
manifold for that zone gets hot -- which appears to indicate
that hot water is not flowing to some of the branch loops in
that zone. When I first turned up the thermostat for this zone,
I heard the sound of water running in this zone's manifold.
Then, when I bled it, there was initially a lot of air bubbles
and rust-colored water before it cleared up leaving only colorless
water. Surprisingly, when I bled it again about 3 hours later
(still with the zone calling for heat), no liquid came out!
Ever since then, with the thermostat still turned up, bleeding
yields colorless water only sporadically. What does this mean?

The other zone in the second floor is even stranger still.
On a call for heat, the powerhead for this zone turns on
the furnace and pump just as for the others. Now, however,
while the pipe (in the furnace room) leading from the hot
water source to the zone valve becomes hot rapidly, the section
of this same pipe downstream of this valve cools off rapidly
to the point that it is merely warm long before it leaves the
furnace room. So it appears as though hot water cannot get
very far pass the valve -- if at all. I tried to determine
if this was because the valve was sticking by removing the
powerhead to see whether the motor assembly and valve stem
assembly rotate freely -- but both seem fine. When I bleed
the valve in the return manifold located in one of the rooms
within this zone, colorless water comes out only occasionally --
most of the time there is nothing. What is wrong?

Thus, so far as I can see, all of the heating controls seem
to be working. Nevertheless, there are obvious problems as
described and none of the thermostats get satisfied. Also,
the problems on the second floor appeared before this summer.
In contrast, the domestic hot water is fine: it is available
when it iscalled for, and there is not any noticeable rust.
I also checked a gauge on the furnace-pump assembly and it
showed a pressure of about 8 psi or 48 kPa, and a temperature
of 195 deg F or 90 deg C. The temperature gauge on the hot
water tank shows 126 deg F or 52 deg C.

Thanks in advance for any helpful feedback.
Old 09-24-04, 11:08 AM
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Your description is very good of the system and your problem. I see a couple of problems with your scenario. One is that there is no primary/secondary loop setup and no mixing valve. You don't want to put water any hotter than about 140 degrees F into the radiant tube and if you are using the boiler for domestic, I would assume that you have to keep the boiler temp higher than 140. Possibly not but probably so. One standard circulator will not be able to supply water to the heating manifolds and also push it through the individual radiant loops. Usually we install a standard circulator (Taco 007) on theboiler to cause flow through the 4 way mixing valve and also provide circulation for the indirect water heater. Then there is a larger pump like a Taco 0010 to move water through the secondary loop which would include the header with your zone valves for the individual manifoids. Each zone valve would be able to start the secondary loop pump, and signal the boiler that there was a call for heat. The indirect would signal the boiler that there is a call for heat but not start the secondary circulator. I hope that makes sense.

Old 09-27-04, 05:45 PM
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Thanks very much for your feedback.

Some of what you pointed out in your response are issues which I had omitted
in my already-long original post for the sake of brevity, so I shall
describe them now.

After the water is heated by the furnace, it passes through a Grundfos pump
and then seems to be mixed with water returning from both the various heating
loops and the hot water tank in a 3-way junction before part of it is
re-introduced into the supply pipe to the hot water tank; the remainder
appears to be mixed in a different 3-way junction with (cooler?) water from
another pipe coming from the furnace in-flow water which then goes into the
hot water heating supply manifold. (This is my guess of the workings of my
system as I am not a plumber and it is sometimes hard to determine the
direction of water flow. Indeed, is there a good way to figure out the water
flow direction when it is not obvious?)
Is this the primary/secondary loop setup and mixing valve you refer to?

You are certainly right in that the boiler temp should be above 140 deg F,
and judging from the temp of the hot water coming from the taps I think it
is (even though this causes me to wonder why the temp gauge on the tank
reads only 126).

In regards to the circulator(s), there is none in or attached to the hot
water tank, and besides the one I already mentioned on the out-flow of the
furnace I do not see any others. Where else might there be a circulator?

Prior to my present problems, all of the heating zones and the domestic hot
water were working as far as I could tell -- which seems to indicate that
the pump(s) were sufficiently powerful. Although I tried to determine the
type and power rating of the above Grundfos pump used, its label does not
seem to contain such information but rather only certain specs such as
15-42 F, S/N, 115 V, 1 PH, etc. which I do not find very illuminating.
Moreover, even if the pump(s) were not powerful enough, the fact that
the 2 zones on the second (top) floor behave so differently suggests that
there are other factors involved.

I really appreciate the points you have raised, and it would be helpful to me
if you could also respond to some of the specific questions in my first post.
Besides what we have already discussed, what else can I do to diagnose the
cause of my problems?

Old 09-27-04, 07:19 PM
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It seems like some of your radiant loops are airbound. There must be a way to balance flow through each individual loop. If one has an air trap, the others will get the flow and that one will be cold. In order to bleed them, you must close all of them and open one at a time to force all flow through one at a time. Then the Taco automatic air vent will let that air out as it returns to the manifiold. It would probably be helpful and worthwhile for you to hire someone to come and check it all out and explain it all to you and get it working now. Then in the future, you will understand and be able to maintain it better on your own. I still say that there should probably be another pump somewhere. I can't tell you exactly where it should be but I would think it would be fairly close to the boiler and mixing valves.

Old 11-02-06, 03:17 PM
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Did you fix up your problems yet

Hi, selfhelp, just wonder did you fix up your problem with your heating yet? I have the same problem as you described in your thread I have a 2 year old, 4-zone controlled in-floor-hot water heating system. And as you dedscribed in the thread, I have one totally cold zone at my home and don't know what the problem is. I will be very happly to hear about your soluitons.

Thank you very much.

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