This is a simple system. FHW on Zone 3. Pumps out to the garage,
through a Modine blower unit mounted near the ceiling. It is new this
year. I turned it on, the zone pump fires up, but the pipes
(plastic), never get warm beyond the first few feet of the return and
feed. There is a little valve on the feed side with a grey plastic
turn screw on the top, looks like something to bleed with, but I'm not
sure how it works. I backed it all the way out, but it seems to make
The Modine unit never kicks in, but I assume there is a mechanism to
detect heat in the pipes before it does. All is pluged in, the zone
pump just keeps running.
Any ideas where to go from here?
I have no experience with the unit, but it seems like there is a
blockage preventing the hot water getting into the unit or the cold
(warm) water getting out of the unit. Are there valves on either pipe
that may be shut off?
Who installed the unit? If a contractor, call him.
Yes, I looked at the Modine unit, but I don't see any valves there. I
really think that there is a air blockage, if that is possible. But I
can't figure out how to bleed it. I did call into the contractor and
I'm sure he'll come out and fix it, but I just like to try and
understand and figure these things out.
I gather from your post you are using a separate pump for each zone
instead of zone valves and a single pump.
Since your pump and HW line are new, I suggest you also look into the
reverse flow from the other zone(s) in your house. The pump will pull
from all connection(s) on the HW manifold. Unless there is back-flow
prevention valve on each zone.
Also, for heat efficiency, you should also have a back-flow on your
garage zone. You don't want to waste heat in the garage.
Run only your new zone pump for 30 minutes or so, then check the return
pipes from your other zone(s) to see if they are hot, warm, or room
temp. Trust me, if the return pipes from your other zones are HOT, you
need to make some changes.
However, I do agree with others that your problem is most likely some
sort of blockage, or the the pump motor is not spinning the pump (i.e.
the pump clutch has one or more broken springs.)
Thank you. I'm not exactly sure what you mean so I'll describe the
setup in more detail. There is a large pipe coming out of the
furnace. There are 3 pipes coming off of this pipe, each one going to
a green pump above it. One pump is for the 1st floor, one for the 2nd
floor, and the third for the garage. Each pump has an electrial
connection to a box on the wall that says something along the lines of
"zone control". Each connection has a corrosponding connection to a
thermostat. Zones 1 & 2 have been operative for over a year and
working fine, the pipes associated with these are hot all the way
through. The pumps are all about a year and a half old, but this is
the first time the Zone 3 (garage) pump was acutally fired up. It
seems to be spinning. When I turn on the thermostat in the garage, I
hear a gurgle of water at the heater, but as I say, nothing get's hot
and the fan never kicks in (Modine unit)
Can you tell me how the valve on the feed end work? They have a grey
plastic knob on the top that I can turn by hand, with a lock nut below
it. If I back the plastic knob all the way up, I can then press it in
and pull it out, but nothing happens.
Yes, I will try to describe what I was talking about:
In some HW setups, there is a large diameter pipe that feeds all the
pumps (as you described you have.) Again in some homes, all the zones
have a return line, and these returns are joined into a single pipe that
feeds the cold water return to the boiler. Thus the water can be re-
heated and re-pumped out to the multiple zones. My personal experience
is the return is about 20 degrees F minimum to maybe 40 to 50 degrees
cooler than the output of the boiler.
(Aside: again from my experience, a thermostat was attached to the water
tank on the boiler, and this thermostat controlled the burner for the
boiler to kick on or off, completely independent of the room thermostat
(s). DAMHIKT, that the boiler thermostat can go bad without the room
thermostats going bad. And you must never, ever, set the boiler
thermostat higher than it is supposed to be set to, which was 180 degrees
in my case.)
The back-flow valve is also called a check-valve. This is nothing you
can control, it is soldered into a part of the pipes. Internal to the
the back-flow valve is a one-way flapper valve that allows the water to
flow only one way in the pipe. Without a check-valve, when the 3rd zone
pump is on, water can flow backwards from zone 1 & 2 as well as normal
flow from the boiler; of course this presumes the pumps for zone 1 & 2
are off. With all three zones pumps working, there will be no back-
Wikipedia has a good write up on check-valves. Google for check-valves.
But, again, I think the most likely cause of your problem is an air
bubble in the line. There must be a small air bleed at, or near, the
highest point of the zone piping. All water has extra oxygen, nitrogen,
or carbon atoms in dilution in the water. As the water is heated,
cooled, and circulated these free atoms of gases will come out of
dilution and form gas bubbles. Small air bleed valves installed at the
high points allow the home owner to manually bleed these air gas bubbles
out of the boiler HW system. Every time you drain and re-fill the
system, you will need to bleed the air bubbles about every month or so.
You may get better instructions on how often to bleed the air on a re-
filled system from another poster on this newsgroup.
Also, there should be a small tank on your system for water expansion so
you don't blow your pipes as the water heats up. It also should have a
separate air bleed valve. Just make sure you plumber shows you this
expansion tank, it's bleed valve, and the location of the other bleed
I know, you know much of this already, and I gave way too much unwanted
No, I didn't know all of this and I truely appreciate you taking the
time to explain it all. Now I guess I just need to find the bleed
valves. Again, I believe the pumps are on the inflow side of the
boiler, right? If so, then on the outflow side there are 3 other
valves. Valves may be the wrong terminology, but they are the pipe
diameter at each end, and wider in the middle. On the top of the
middle there is a brass nut with a grey knurled knob on top of it. I
can unscrew this knob and them pump it up and down, but it doesn't
seem to be doing anything. So I backed off the lock nut and tried
it. Again, no joy. Would this be the "air bleed valve"? What does
one typically look like?
Could be. Your mileage may vary. The system on my home 9 years ago had
the pumps on the outflow (Hot) side of the boiler. The garage zone pump
caused the reverse flow in my old system. It is very possible your pumps
are on the return side. I had a push system, yours could be a pull
Only the installer (or someone familiar with your type of system) can
tell you exactly what these are. This media of text only is too
difficult to get it correct.
Usually located at the highest point of the system, in your case I would
look near or on the heat exchangers (baseboards, radiators, or whatever)
on each zone.
see chrome square nut drive in link below:
Your Modine unit will have one. It may be behind some of the extra sheet
metal covering the left or right sides of you unit. Look for a service
hatch near where the Hot Water enters the unit. But the bleed valve will
(should be) at the highest point of the plumbing for that zone.
By the way, I just had a thought, do you have a pressure gage on your
system? Is your Hot Water system up to equal system pressure as your
domestic potable water system? With no pumps running, do you have about
60 or 80 PSI water pressure in your lines?
Hmmm, good point. The unit I have looks like this one:
There is a connection at the top and one at the bottom. I assume the
return is the one on the bottom?
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