Original message
| pdt1842
 |  "Unable to hold heat - Hydronic system"
, posted Mon 11 Feb 16:09  
I have a tri-level house with basement heated by a 3 year old Burnham hydronic boiler which replaced a 40 year old American Standard boiler that finally called it quits. Each level has its own zone(s), the thermostats (Honeywell T87K) were just replaced and are properly opening/closing valves, set for 3 cycles per hour as noted in the thermostat setup. The boiler is set for 180° and cycles (so I know I'm not at the boiler's capacity), but I am unable to hold heat on the main level especially when outside temps are below 15°F, but no problems on the other levels. The main level is serviced by two zones, so I don't think I should be having this issue. House is well insulated and windows are all low-E thermal pane, so heat loss is relatively minimal compared to what it was when we bought the house 5 years ago. I had no problems the first heating season with this new boiler, but this year has been a pain in the neck, with temp swings of 5° not uncommon.
My boiler contractor is stumped on this one, as this didn't start occuring until last year. I have some air in the lines - which is really irritating to listen to - but none of the zones are airlocked. Zones appear to be fairly well balanced.
I'm at wit's end right now, and am tired of fighting this. Does anyone have any suggestions as to where to turn next, trying to solve this? Thanks.
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Replies:
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| wet head
| "Re(1):Unable to hold heat - Hydronic system" , posted Mon 11 Feb 17:24
some things to check,
- temp of water leaving to zone hand temp returning, baseboard heat normally operates on a twenty dgree temp drop from supply to return. if water temp is less than that than you need to check baseboard placement, obstructions, dirty elements.
if water temp is more than twenty then you are probably not moving enough water trough the lines. in that case i would suggest increasing the circulator to a taco 0010 or 0011. grundfoss also makes a nice pump there model 99 is a three speed circ more money though.
-why is your t-stat set for three cycles per hour? how long do these cycles last? does it kill the heat call before it has made temp? first floors can be hard to maintain with warm air rising to the seccond and third, maybe you are not running the heat long enough.
- has anyone done a leat loss calc on your first level? do you even have enough element to keep up?
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| | pdt1842
| "Re(2):Unable to hold heat - Hydronic system" , posted Mon 11 Feb 17:49
Thanks for the response and suggestions.
Current circulating pump is a Taco 007-F5. No obstructions to the baseboards, so I have decent ventilation/convection. I ran a shop vac w/brush over all the elements before the start of the heating season.
Stat calls for 3 cycles per hour (10 min on, 10 min off), but I've noticed that as long as the system is calling for heat, it doesn't seen to be adhering to that cycle pattern. I can change it to 5 or 9 cycles, but I don't think that would make a difference other than running short cycles.
Didn't seem to have a heat loss problem before (that is, with old or new boiler) until this year; plus, I added 8" of insulation to the attic this fall, bringing my total to about an R59 value - and for our area, that's probably overkill.
I've turned the water temp up to 190° and turned back the setting on the upstairs stat for the interim, to at least get the main level warm. System is holding steady at 20lbs, so I think I'll be ok with that increased temp.
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| | wet head
| "Re(3):Unable to hold heat - Hydronic system" , posted Mon 11 Feb 20:17
i would set that limit back to 180 and try to do something about that t-stat. 10 min on 10 min off no more than three times an hour. on a zero degree day your first floor will more likely want to run 20-30 min 0n 10- 15 min off. i would at least try eliminating your t-stat issue before making adjustments to your boiler. a properly sized boiler should never be set over 180 degrees. pull the t-stat off the wall and twist the r & w wires together and just wait to see if it makes temp. even if it takes an hour. it is no big deal to let your circ run and run to heat the space, as long as it eventually makes temp. if it was your boiler that ran without downtime i would say you have a problem.
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| | theduke03
| "Re(3):Unable to hold heat - Hydronic system" , posted Mon 11 Feb 19:22
I agree. 3 cycles per hour may not be enough to heat the 1st floor. Especially on cold days. That setting does not control runtime, only the # of times it may turn on in one hour. Are all your baseboards hot when those zones are calling for heat?
You can't put a price on comfort! Be Safe.
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| | pdt1842
| "Re(4):Unable to hold heat - Hydronic system" , posted Mon 11 Feb 22:26
Appreciate everyone's input.
1) Boiler thermostat is off - setting at 190° is only giving me high temp of about 170-172°. This might be part of the problem.
2) Even though I have the wall thermostat set at "3" (3 cycles per hour), that seems to be over-ridden if the thermostat is calling for heat - e.g., I have one thermostat that has been calling for heat for the past 30 minutes, and the zone valve has remained open.
3) Does the presence of air in the lines effect my thermal conduction? My boiler guy says "no" but I can't seem to feel that I'm not getting full thermal transfer due to the air in the lines. I hate to bleed air right now as the refill water is just so darn cold that I'll end up with more air than I currently have. This is the strangest thing, though, as I bled the entire system before the heating system started, but it seems to be getting worse. I've shut the fill valve off and kept an eye on the pressure gauge for a week to see if I have a leak, but pressure is remaining constant. Expansion tank was replaced last year, so that shouldn't be an issue.
4) Baseboards are all hot, so I've ruled out an airlock in the system.
Again, I appeciate all the replies and suggestions. My wife tells me I'm obsessing with this - and she's probably right!
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