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Old 02-28-2011, 12:09 AM   #1
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questionable top zone diagnosis


I have a 12 yr old super hot boiler with a 007-F5 pump and 6 zones. The top zone will only heat up if all the other thermostats are tuned off. This happened 4 yrs ago and the fault was solved with a pump replacement but it's now happening again. The top zone is the furthest & highest & is only piped in 1/2" pex compared to the 1 " pex going to the other zones. All the pressures, temp and excess air seems normal. It was explained last time that the flow resistance to 1/2' pex going up three stories causes too much flow resistance for this pump when it's not 100%. There are no bleed valves on the baseboard heaters but I am assuming it's not an air lock as it can work when it's only on by itself. Does this diagnosis seem possible and should I then replace The 007 pump with an 008 pump instead?

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Old 02-28-2011, 01:04 AM   #2
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questionable top zone diagnosis


If your worried about the pump do an amp draw on it, one of the easiest methods of seeing if it's working. My self i live in an area where we don't have to worry about any build up in the pipes, that said I would look at flushing that one loop independently of the others.

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Old 02-28-2011, 01:53 AM   #3
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questionable top zone diagnosis


hey Adam
I don't doubt that the pump is working. It's heating all the other zones perfectly well. It will even heat the top zone if the entire force of the pump is directed to that zone by only having that one zone call for heat.
The problem is that when that pump force is shared by the opening of any other zone, the top zone stops heating. All the zones are physically opening and closing properly. My question is if the inside diameter of 1/2 " pex pipe ( which has a smaller inside diameter than 1/2" copper) is too restrictive to adequately circulate hot water up three stories through a baseboard heater and back, when that pump is also diverting it's pumping pressure through lower and shorter 1" pex runs. There are engineering formulas that with some study will give me this info but I was hoping that some body familiar with zone heating would know off the top of their head.
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Old 02-28-2011, 03:11 AM   #4
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questionable top zone diagnosis


Most hydronic piping is done in 1/2" that 1" you see goes off to a header somewhere and drops down to 1/2".
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Old 02-28-2011, 03:16 AM   #5
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questionable top zone diagnosis


Darn phone, hit send too early. check your water pressure if it's below 15-25 psi might be an issue. Also try to flush water through that zone,manually turn on that zone valve as well as a drain somewhere close to the return loop before the boiler. This can achieve two items pushs air out and can take debris out of the line.
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Old 02-28-2011, 06:03 AM   #6
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questionable top zone diagnosis


What is the water pressure in your system when this is happening? How high above the boiler is the baseboard of the third zone? 20' 25', 30'?

Your water pressure is probably just a little to low to circulate water through while the other zones are also calling.
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Old 02-28-2011, 11:04 AM   #7
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The water pressure is between 22 and 26 psi, the baseboard is 28 feet above the boiler.
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Old 02-28-2011, 11:18 AM   #8
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questionable top zone diagnosis


By your description it certainly sounds as if the pump is sized on the hairy edge of capacity, and when you replaced it 4-5 years ago the fresh impeller was capable of meeting the flow required when multiple zones are calling for heat, over time an impeller will erode (loose efficiency) and the zone with the hightest pressure drop will not be fed the GPM required to meet the demand.

In order to advise on the replacement pump, more information would definately be needed, such as, # branches, valves, fittings and total length, but again it sounds like the pump is sized to close to the flow vrs pressure drop required.

Mark

Edit ----- In looking at the curves for an 008 it will increase your operating pressure, but it could reduce the system total flow, resulting in an even worse condition.

What is the differential pressure, inlet to outlet of the pump?
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Last edited by Jackofall1; 02-28-2011 at 12:21 PM.
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Old 02-28-2011, 01:59 PM   #9
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questionable top zone diagnosis


That's a TACO pump with a replaceable cartridge. The OO7 model doesn't have a great pumping ratio to head pressure, so you will have flow issues when the other zones with less resistance open up and the pump will push to the zones with less resistance. If replacing the pump worked last time , you could probably replace just the cartridge this time and save a few bucks if you are happy with marginal performance. A 008 pump has a much higher head that it will pump against and should give you the pressure you need to get to the top floor. The GPM isn't a huge concern in this type of system as pipe sizes are fairly small and won't likely exceed total GPM of the pump.
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Old 02-28-2011, 03:14 PM   #10
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questionable top zone diagnosis


How much pex is in that upper zone?

1/2" pex at 120F water temp has a head loss of 3.804 foot for every 100 foot of pex at a 1 gallon per minute flow rate. At 180 its a 3.171 foot loss. And at 2 gallon per minute its 13.159 foot of loss at 120, and 11 foot at 180.

What water flow rate was your baseboard sized for?

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