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Gas Fire Water Heater Continuously Runs

Written By Wednesday 26 October 2022 Add Comment Edit

  1. Garage heater power vent runs continuously

    I have a reznor ua-100. The power vent fan motor runs continuously while the power switch is on. Since the power vented exhaust is currently hardwired to AC it is running as expected. This garage heater has always been used as temp heat for garage when turned on and shut off via main power when not is use. moving forward this unit needs to be on 7x24 in the winter to keep above freezing but having the power vent running continuously is not acceptable. I was wondering if I bypass the thermostat on the 24 volt circuit and instead install a 120 volt AC thermostat on the input AC. This would prevent the power vent from running when the thermostat was not calling for heat. The only downside I see to this solution is that the thermostat cuts of the AC when the room set temp is reached. The AC thermostat will shut off the main blower and the gas valve. Normally there is a period where the main blower runs after gas valve is off to cool down to low limit threshold which will not longer occur with the new thermostat.
    This has not been a problem in the past as the AC power is shut off manually when temp use is no longer needed when the last person leaves. However this will be happening alot more at the end of every heat cycle if I change to and AC thermostat on the input AC. Is there a downside to this solution? Anyone have see any concerns?
  2. Damage to the heat exchanger from the fan not having its extended run time.

    Just have a tech come out and find and fix the reason the venter fan keeps running.

  3. The power vent fan is currently hard wired to AC power. This is how it was originally installed and used for many years. So the heat exchanger could be damaged by not getting the cool time via fan after the burners are off.

  4. Quote Originally Posted by mmeizis View Post

    The power vent fan is currently hard wired to AC power.

    That is not correct. Have your tech wire it correctly, or find the reason it got wired like this.

    �I haven�t failed. I�ve just found 10,000 ways that won�t work.� - Thomas Edison

    �It�s not whether you get knocked down, it�s whether you get up.� - Vince Lombardi

    "In this house we obey the laws of thermodynamics" - Homer Simpson

    Local 486 Instructor & Service Technician

  5. Quote Originally Posted by mmeizis View Post

    The power vent fan is currently hard wired to AC power. This is how it was originally installed and used for many years. So the heat exchanger could be damaged by not getting the cool time via fan after the burners are off.

    Then it was never installed correctly.

    And yes, it can be harmed if it isn't cooled down properly.

    You need a tech that knows what he is doing to resolve this.

  6. the schematic on the inside cover includes all the components except the power vent fan. Everything appears to be wired correctly. The power vent must have been and add on when originally installed since it is not in the schematic. Is a power vent necessary for the ua-100? The vent pipe is vertical. the power vent is an external attachement to the vent pipe and hard wired to the external ac power sw. Does anyone have schematics for the reznor ua-100?

  7. Quote Originally Posted by mmeizis View Post

    the schematic on the inside cover includes all the components except the power vent fan. Is a power vent necessarily for the ua-100? The vent pipe is vertical. the power vent is an external attachement to the vent pipe. Does anyone have schematics for the reznor ua-100?

    Call a licensed and insured contractor.
  8. Should be a easy fix for a licensed tech.

    UA Local 32 retired as of Jan 2020

  9. Quote Originally Posted by mmeizis View Post

    The power vent must have been and add on when originally installed since it is not in the schematic. Is a power vent necessary for the ua-100? The vent pipe is vertical. the power vent is an external attachement to the vent pipe and hard wired to the external ac power sw. Does anyone have schematics for the reznor ua-100?

    The UA series is a late 1970's unit heater, and even Reznor states on their website that no manuals or parts are available for this old model.

    I would guess that the manual for this unit never existed in pdf format anyway - paper manual only.

    Yes, the power venter is an add on.

    As far as is it needed - even on a vertical flue, a negative space pressure would require the use of a power venter.

    Instead of learning the tricks of the trade, learn the trade.

  10. Quote Originally Posted by mmeizis View Post

    the schematic on the inside cover includes all the components except the power vent fan. Everything appears to be wired correctly. The power vent must have been and add on when originally installed since it is not in the schematic. Is a power vent necessary for the ua-100? The vent pipe is vertical. the power vent is an external attachement to the vent pipe and hard wired to the external ac power sw. Does anyone have schematics for the reznor ua-100?

    Depends on how it was installed.
  11. Thanks, the UA-100 has been working well for temporary use when people are in the garage, 1600 sq ft. I am OK with the power venter running all the time while we are working there, but I am not comfortable with the power venter running 7x24. It would eventually burn out and being discontinued difficult to replace. i really wanted to find a solution so I could lower thermostat to 40 degrees and run the UA-100 7x24 in the winter to keep liquids from freezing in the winter. I guess I'll just keep reznor ua-100 the way it has been working all along and build an insulated cabinet and put a baseboard heater with a thermostat in the cabinet. Better than springing for a new garage heater. Although given the age I may have to break down and get a new heater sooner than planned anyway..
  12. It would be very simple to change some wiring so the power vent only ran when the unit was calling.
    Running constantly means your pulling all the heat back out of the space. Unless you've run a separate combustion air supply to the unit.
    40* is too cold for the unit. The flue gasses will condense and cause damage. That unit should be checked for heat exchanger cracks anyway given it's age.

    �I haven�t failed. I�ve just found 10,000 ways that won�t work.� - Thomas Edison

    �It�s not whether you get knocked down, it�s whether you get up.� - Vince Lombardi

    "In this house we obey the laws of thermodynamics" - Homer Simpson

    Local 486 Instructor & Service Technician

  13. Quote Originally Posted by mmeizis View Post

    I guess I'll just keep reznor ua-100 the way it has been working all along and build an insulated cabinet and put a baseboard heater with a thermostat in the cabinet. Better than springing for a new garage heater. Although given the age I may have to break down and get a new heater sooner than planned anyway..

    I am curious, why not have someone come in and correct it? Second question, is the power venter part of the unit or is it in the duct work and was added to the unit? Either way as stated earlier it would not be hard or difficult to wire it the way it should have been originally.
  14. Thermostat starts venter, vent proving switch fires heater...

    Is this too much info for AOP? If so I will amend...

  15. Yes the power vent is inline in the duct about 6 inches outside the back of the unit. This is a simple unit. it does not have a control brd. the only components are the fan motor, limit control sw, fan control, gas valve, 24 v transformer, thermostat, power vent fan and vacuum sw for power vent fan.

    A little about my background: Electrical engineering, Ran data centers for 15 years, currently retired and managing an apartment building. i have fixed the furnaces in my apartment building for many years. i do not throw parts at it and do actual troubleshooting. Over the years, I have changed limit switches, starter caps, power vent motors, fans, thermisters, igniters, flame sensors, tested gas pressure etc. I will always leave whole unit installs, freon leak testing, compressors and freon charging to the licensed professionals. I have an HVAC tech coming out Monday to track down a freon leak in one of my AC units. I will ask his opinion on the matter while he is here. i have a feeling he will be reticent to modify it from the way it has been working but I can ask. My experience is the average field tech is trained to troubleshoot something that has failed and higher level of understanding is required to modify a "working" unit without undesired consequences.

  16. That was my original thought too originally. However, there are issues.

    My first thought; hook it up in parallel with the main fan, however the main fan does not run until the plenum temp is reached and the power vent will restrict air flow until the fan goes on. When the gas comes on the power vent needs to be running.

    2nd thought: buy a relay to turn on the power vent fan on when the thermostat calls for heat. the relay could turn on 115 to the power vent when the gas valve gets its 24v. But this will not work because the power vent vacuum sw. is in line with the thermostat so the gas valve will never get 24v to turn on.

    3rd thought; Put and 115v thermostat on the entire unit. thermostat calls for heat, power vent comes on, gas valve opens, after plenum is warm main fan comes on, thermostat stops calling for heat, 115v is off, Plenum is still warm, problem, main fan should run to plenum low limit but ac is already off.

    i think i have a solution
    Put a 115v thermostat only on the power vent motor. Thermostat calls for heat, power vent fan goes on, power vent vacuum sw closes, 24v to gas valve, gas valve opens, plenum low limit reached, main fan goes on, thermostat stops calling for heat, power vent stops, power vent vacuum sw. stops voltage to gas valve, main fan continues to run to plenum low limit.

    40 degrees is too cold? what is a good low thermostat temp when noone is there? The garage is well insulated and holds heat well until i open the 10 ft door. I want to keep fuel cost to a minimum but not freeze the liquids. This is an 80 percent efficient unit with a double insulated vertical flue through the roof.

    There is not separate air supply for combustion, so with the power vent always running i am paying to heat the outdoors too. another reason to find a solution.

    i had the unit cleaned and checked out almost 2 years ago. i have not used it much this past couple of years but just filled it up the garage and will be using it more now. They did not mention anything about cracks. I did not ask specifically to look for cracks. They never mention the fact that the power vent runs continuously.

  17. Way too much info for the AOP.

    Old unit
    Add on power vent
    Homeowner doing the work

  18. If you have a tstat to control how hot you want to keep the room and the only reason you turn it off at the power switch is so the fan doesnt run all the time, then it's not wired correctly. Don't try and add more to the mess, just get fixed what isn't right and get it inspected before you become a statistic.
  19. bluegrass heating is coming out tomorrow. Sounds like i'll need to buy a 115v thermostat to replace the 24v one. Something he probably won't have on his truck. Thanks everyone for the feedback, hopefully he'll get it taken care of tomorrow.

  20. Quote Originally Posted by mmeizis View Post

    bluegrass heating is coming out tomorrow. Sounds like i'll need to buy a 115v thermostat to replace the 24v one. Something he probably won't have on his truck. Thanks everyone for the feedback, hopefully he'll get it taken care of tomorrow.

    Now I�m really confused!

cloutierfamem1974.blogspot.com

Source: https://hvac-talk.com/vbb/threads/2206931-Garage-heater-power-vent-runs-continuously

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