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Old 01-23-2011, 08:40 AM   #1
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HVAC return line keeps going cold

Hello everyone, I'm a maintenance tech at a hotel and am having an issue with a heater that I can't seem to nail down. Admittedly I'm not an expert in the heating department but I know enough to normally keep them running, and this might be a simple answer. We've got a real cold spell coming so I'd like to get it straightened out.

The HVAC has hydronic heat and the coil and both pipes stay hot when in the 'Off' position (zone valve open), but within a minute of turning the heat on, the return pipe starts going cold while the supply stays hot.

There is a room above and below this particular unit and both of them are tied into the same lines and neither one of them is having any trouble. The coild doesn't seem to be frozen, the t-stat seems to be operating just fine, as does the zone valve. When I bleed it I seem to get a tiny bit of air but no blasts like from an HVAC that is airbound. There also don't seem to be any leaks anywhere.

Any ideas on what this issue could be? Any help appreciated.


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Old 02-02-2011, 09:18 PM   #2
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I'm going to bump this in hopes of a response.


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Old 02-02-2011, 11:10 PM   #3
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Sounds like everything is just the way it supposed to be, the return line is cold or cooler because of the heat exchange that is happening in the room or rooms the system is supplying.

When its all said and done there is usually more said than done
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Old 02-03-2011, 02:30 AM   #4
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Does the return warm up a few minutes later while the fan is still on, or does it stay cold?
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Old 02-03-2011, 05:43 AM   #5
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Just to update, the pipe kept getting cold because the room itself was so much colder than normal, just like you say Jackofall1. I had never had one go that cold on me and it took it a couple days to actually get back to normal. We had a similar problem one time and it ended up being frozen, I was trying to narrow down where that might be, but it wasn't frozen after all.

Thanks for the bump, I appreciate the help. This is a great forum to read, I've learned quite a bit.
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