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Old 12-13-2010, 11:36 AM   #1
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forced hot water not getting to 2nd floor


We have two-zone forced hot water system which intermittently stops getting water to the second floor. The first floor is baseboard heating, and the second floor uses radiators. I can get the water moving upstairs by releasing some water from the blow-off valve for a second or two, which, if I had to guess, creates a siphon. This rapidly moves the water upstairs, and once I do this, it works fine for two or three days, but then gets stopped up again. When this happens, several feet of the return pipes are hot, and the outgoing hot-water pipe is cold. We had a repairman come out twice, and $600 later he bled the radiators and replaced the expansion tank, which was probably not broken to begin with. My only guess is that the circulating pump is defective, as it allows water to move backwards through it, but you can hear and feel it working when the thermostat is on, and the repairman thought it was fine. The other possibility is that we have a leak, but it doesn't seem like the system is losing pressure. When cold it is around 10-12 psi, but when everything is working it gets to around 15 psi.

The other possibility is that since both zones switch on at the same time, that the first floor cycle completes, and the water just never starts moving to the second floor.

The system has a similar set up to the one in the link below, with differences in the placement of some valves and the expansion tank:

http://static.howstuffworks.com/gif/...n-system-1.jpg

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Old 12-13-2010, 01:37 PM   #2
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forced hot water not getting to 2nd floor


well what it could be is that you have an air loop in your system. which means that the upstairs is full of air so it wont let the water up there. bleed the lines. at every hearter upstairs. becareful as the water is hot. and if this fixes your problem you might have a leak, or there is air getting into the system some how.

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Old 12-13-2010, 01:48 PM   #3
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forced hot water not getting to 2nd floor


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Originally Posted by hvac kid View Post
well what it could be is that you have an air loop in your system. which means that the upstairs is full of air so it wont let the water up there. bleed the lines. at every hearter upstairs. becareful as the water is hot. and if this fixes your problem you might have a leak, or there is air getting into the system some how.
Have bled the radiators several times, and there is very little, if any, air coming out. And when the system is stuck, the water coming out is not hot at all.
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Old 12-13-2010, 06:54 PM   #4
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forced hot water not getting to 2nd floor


Might not have enough water pressure.
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Old 12-14-2010, 11:17 AM   #5
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forced hot water not getting to 2nd floor


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Might not have enough water pressure.
When cold, the pressure is right around 12 psi. When hot, it gets near 20 psi. The furnace is located in the basement, so it needs to travel up two flights to get to the third floor. I could get the pressure up, but I am worried that if I raised it to 15 psi when cold, that the relief valves, which are set to 30 psi, might then fire and drop the pressure back down to 12. Also it just doesn't seem like there is any connection between the pressure on the gauge and water getting up to the second floor. Is there a way I can check to see if the pressure might be the problem?
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Old 12-14-2010, 08:07 PM   #6
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forced hot water not getting to 2nd floor


How high is the highest rad/baseboard above the boiler. Each 1 PSIG will raise water 2.3 foot. So if your highest rad/baseboard is 30 foot above the boiler. Then you need 13 PSIG just to reach that rad/baseboard. And should add 3 to 5 PSIG to that to get good flow using a standard circulator.

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