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short cycling system

Weezbo Member Posts: 6,232
familiar with the system you own.

you may have to just agree with the radiantec and polaris guys that it is working fine. perhaps through agreement it will preform according to the arrows on the paper.

it may be just too deep to delve. i am not certain.

any pictures?


  • T Hawkins
    T Hawkins Member Posts: 2
    radiant system short cycling

    I have a hydronic system engineered by Radiantec,50 gal. Polaris heater (gas) 3 zones, 2300 sq. ft. live in central Illinois, well insulated 6 year old home. Problem is constant short cycling of the polaris unit, I have also had to replace the Hot surface igniter 7 times in 6 years of service, the control module has been replaced as well as new gas valve. Supply temp is always @ 150, return usually 15 -20 degrees lower, unless it has not ran for awhile, then return side temp is down to room temp. In phone conversations w/ polaris and Radiantec after describing my installation and e-mailing pictures they both think everything is fine. I have not been able to find anyone in my area (61817) that knows much at all about this type of system for service/repair. Winter bills I think have been much too high for this type of system, I'm sure it could be more efficient if "tuned up". Any suggestions at all would be appreciated.
  • Brad White_40
    Brad White_40 Member Posts: 31
    You say that the system runs constantly at 150F

    Is there no outdoor reset? Are the heater loop and radiation loops de-coupled so you can use deep re-sets without condensing in the heater? (I am assuming the Polaris is non-condensing).

    Without knowing what your calculated heat loss is, how much radiant surface you have at what design temperature and what size the heater is compared to those, there is no way to start helping you.

    At first I would say that the costs of energy are up everywhere, but the igniter replacements do indicate a failure rate that is obviously unacceptable. You are probably stocking spares now, I bet. Ask Radiantec and Polaris how annual replacement of igniters is acceptable.
  • Ron Schroeder
    Ron Schroeder Member Posts: 998

    What is the differential on the heater's aquastat?
  • T Hawkins
    T Hawkins Member Posts: 2
    Short cycling responses

    thanks for the responses, as for some of the technical mechanical questions raised i will attempt to answer some, although I did install the system myself along with a plumber friend I am only an Ironworker not real hvac mechanically proficient! ( I do change the H.S.I. the air sensor and control module when they all have failed though).As for the outdoor reset there is none, the polaris unit has excesive condensation going on due to the short cycling as the polaris techs have explained. As for the calculated heat loss, sorry I dont know that answer. the unit is 94% efficient,w/ input rating of 100000 btu/hr, it does perform potable and space heat, w/stainless lined tank. I certainly agree energy cost are up, however I feel this system never has performed at its most efficient at all. also looking back on my notes the H.S.I. has been replaced 8 times now as well as an air sensor once. The heat supply and return are plumbed out of the top of the unit as described to do by both radiantec and polaris techs in the begining, however after recent conversations w/ techs they say it should be plumbed from the sides of the heater that do have supply and return nipples marked! Would this truly make any difference? There also is no expansion tank anywhere in the system would this make a difference in a closed system such as mine. Yes I do have spare H.S.I. on hand! thanks again !
  • Blackoakbob
    Blackoakbob Member Posts: 252
    Polaris piping...

    What I have have done with my installs is, pipe out of the side supply and return to a flat plate heat exchanger using a bronze or stainless pump. Then on the heating side of the system I use a typical piping arrangement: supply out of the HX to spirovent with auto fill valve and backflow preventer, circ pump or pumps as needed, thru the system and back to the HX. I run the pump from the polaris on a summer winter switch and cycle the heating pumps with thermostats. The polaris has to run for hot water as needed but with the required supply temp @ 150 degrees I have a HW tempering valve on the domestic supply side for safety. I have had ignitor failures on one system and have been unable to find the reason (yet) I believe it maybe gas pressure set up related. Remember you are sharing your heating system with your water heater so a 60,000 btu heat load and a 55,000 btu water heating demand leaves you with a negative btu supply @ 100,000, which could lead to odd cycle rates. These premix burners do require correct gas pressure adjustment and are seldom correct out of the box. Best Regards, TH
  • hr
    hr Member Posts: 6,106
    The differential is too tight

    on the Polaris control. Something like 2-3 degrees as i recall, non adjustable. I crank that stat all the way up and, turn it into the high limit so to speak, use a setpoint control operate the Polaris with a 15 degree diff. or so.

    The commercial Polaris units have a higher temperature aquastat, 180 I believe, if yours does not allow a high enough setting to do this.

    I have a handful of Polaris/ hx units out there running like this, six years on a couple with no ignitor replacements!!

    I agree they need to be checked with an analyzer to affirm clean efficient burns.

    In the past the factory tech support has been very good. Polaris I mean. Not sure about the company you bought the system from. They should be aware of this problem, The tech fellow I spoke with, years ago at Polaris was aware of the tight diff issue when used as a radiant source. He even told me how to add that control internally. Although unless you want to void or compromise the warranty, add the setpoint to the incoming line.

    Factory support may have changed with the new owners of Polaris. I know the price sure has :)

    hot rod

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  • kinglerch
    kinglerch Member Posts: 14
    edited September 2009
    Improve the Polaris efficiency by

    increasing the temperature differential. It's pretty easy. The above posters are right that there is just about 3 degrees between the water temp and temp setpoint before the heater turns on again. And for radiant heat, my polaris was cycling on then off then on just a minute later. Such a waste...well, here's the easy answer:

    When the burner is on, 120VAC is present on the ignitor. I am using this to power a (very important spec) 120VAC powered relay coil. So just wire this relay to the HSI and HSIG inputs of the Ignition Control board.

    I then take one side of the relay output contacts and wire it to the thermostat board (orange wire, where it says 'POT') and the other side through a 7500 ohm resistor and also to the thermostat board (other orange wire).

    What happens is that when the burner is on, the resistance to the thermostat board will be reduced, causing a temporary increase in the temperature setpoint of about 20 degrees. i.e. at 100 degree setpoint, the increase is 28 degrees (128) at 120 setpoint, the increase is 20 degrees (140), at 140 setpoint, the increase is 16 degrees (156 degrees)...you get the idea. You can calculate the resistance, but with the polaris thermostat they are all approximate anyway. Just remember your higher setpoint will be about 20 degrees above what the thermastat says.

    Once this higher setpoint (128, 140, or 156) for the water is reached, the burner turns off and the 120VAC relay opens. Then the setpoint is back to the original value (100, 120, or 140). This should reduce the cycling significantly and make this more efficient for space heating...all for less than $10.

    Also, this may reduce the condensation problem since you are firing the burner always at a higher temperature, even though the water temperature can fall 20 degrees lower.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Link does not work.

    hr: the link to find a professional does not work.
  • scott markle_2
    scott markle_2 Member Posts: 611
    polaris control

    I ran a radiant slab in a tightly insulated structure (my house) for years. It cycled like mad when i first put it in. I attached a timer to the ac power so that it would run for about 10 minutes every hour, the circulator ran continuously.

    This actually worked pretty well, and bringing the tank temperatures down to close to room temp every cycle was good for condensing.

    I did wonder if cycling the AC power on and off was good for the electronics.

    If I was going to do this now I think I would use a Tekmar 256 reset control. Put the boiler sensor in an immersion well, turn the potentiometer on the polaris to a high limit setting (or max)., and break/make continuity of the polaris potentiometer leeds (orange wires) with the boiler demand contact on the 256.

    I suppose if you were concerned about warrantee issues you could do the same thing with a relay and use the boiler demand to turn AC power on and off as HR has suggested.
  • kinglerch
    kinglerch Member Posts: 14
    edited September 2009
    Polaris Thermostat

    I have had a lot of luck with my "relay upgrade" noted above. The best part is that you can change the R value to whatever temperature differential you are looking for. If R=20K you get 7-15 degrees differential, if R=7500 you get about 15-25 degrees, for some examples.

    But last night I did further testing on my Polaris, and something important came up...the temperature dial is grossly innaccurate. I put an ohmmeter on the POT lines and turned the dial. There are markings for 120 degrees, 130 degrees, and 140 degrees...but they are way off.

    Because the thermostat inside the heater has to be compared with the temperature dial, only the resistance is important. And I found 100 degrees to be top dead center, where the sticker said 120 degrees was actually 140 degrees, and where the sticker said 160 degrees was actually 185 degrees. This is because the thermostat is non linear and when you get near the higher temperatures, you only have to turn the dial a hair to get 10 degrees of temperature change.

    To be honest, the actual temperature isn't normally that important for DHW because as cold water rushes in, the temperature of the water is cooled considerably. It may make more of a difference in space heating because no cold water is being added.

    But the main reason I point this out is the relative temperature. Users of this heater may be shocked to find out that turning the temperature dial from 100 degrees to 120 degrees is about 1/4 turn. But then 120 degrees to 140 degrees is way less, and from 140 to 180 degrees looks like almost no turn at all.
  • kinglerch
    kinglerch Member Posts: 14

    for those that want to do this upgrade, here is the schematic
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