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Discuss CALLING REZNOR EXPERTS :) in the Commercial Plumbing Forum area at

  1. nicholas Veitch

    nicholas Veitch New Member

    Good Afternoon

    Not sure this is the right section for this question but will start here and move if you think there is a more suitable section for it.

    I have a garage workshop car repairer modern building it is fitted with a suspended from the ceiling Reznor Gas heater model UDSA043

    This thing has performed faultlessly for 6 years since install, the last three months it has been behaving erratically, basically it wont start when the ambient temp in building is low, ie. below about 14 degrees.

    if the temp is above that it will start, we had someone have a look at it about two weeks ago, there was some wiring tidied up as the connection on some of the wiring blocks were slack etc

    It worked every morning till this morning, today was the first low temp day since the day the wiring was looked at, so it would appear the same problem exsist's

    So it looks like the wiring is not at fault as the same problem is still persisting.

    basically works when ambient room temp is reasonably high but will not work at all when temps are low.

    This is an odd one !!
  2. Gasmk1

    Gasmk1 GSR

    last time it was serviced or any parts replaced also what controls
  3. nicholas Veitch

    nicholas Veitch New Member


    The guys that supplied it came out and had a look at it first, they pressed the small reset button and it fired, but by then it was midday and the temp was up a bit, that was coincidence, tried that a few times and doesnt do anything.

    They gave it a look over and said all was okay, i knew i would have the same problem the following morning and i did, i asked them to replace the probes while they were there.


    2019-01-17 13.46.18.jpg
  4. bacon_sandwich

    bacon_sandwich GSR

    It sounds (by the statement about resetting), that you are experiencing a flame failure detection. These are very simple heaters and you can usually tell whats wrong by listening to the start sequence. Is the heater easy to access or is it so high up you can only get to it with a cherry picker, lol.... Sadly if its is intermittent, then it can take longer to work out what is wrong. A good service is always a good start and i mean one where ignitors are cleaned and reset, gas pressure checked and gas rate checked, Co2 etc
  5. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Get it serviced and go from there
  6. nicholas Veitch

    nicholas Veitch New Member

    Hi thanks for reply, ignitors were changed, on the initial site visit, i asked the firm to service it while they were there, the reply i got was there is not much to service on these heaters. We have checked it, and it appears to be running fine

    gas pressure was also checked at my request 19mb

    its driving me up the wall, i will see if i can get serviced though

    i can get up to it so i am interested in what the start sequence is

    is the little motor top right hand side supposed to start first, because the times it works thats the first thing i notice

    Then when it doesnt work, there appears to be no sequence no noise from anything just silence and no start

    2019-01-17 17.06.06.jpg
  7. Last Plumber

    Last Plumber Plumber GSR

    You need a commercial Gas Safe Engineer to sort it for you.
    It doesn't sound like much of an issue to be honest.
  8. bacon_sandwich

    bacon_sandwich GSR

    Looks is reasonable nick. If it has locked out, there is a reset button bottom right, if the lamp has failed it may be locked out but not showing a red lamp, press reset button. If the controller has been wired for remote reset you can press that (lockout button) , there should be an immediate response (noise) from the heater, if not its dead.
    Forum rules prevent giving diagnostic information to Non Gas safe people. User can press reset once and then its call an engineer, they are really straight forward, its getting to it with test equipment is the hard bit.
  9. nicholas Veitch

    nicholas Veitch New Member

    cheers for the responses guys i have every intention of getting gas safe to repair, i am just trying to do some leg work first. to see if anyone has come across this scenario before.

    i have tried both reset buttons the red flick switch on the outside. and the small reset on the relay on the upper lefthand side.

    i was intrested in the firing sequence as in does the heater actually run before trying to fire. as this one is doing nothing when it is cold it is not running at all.

    is there any truth in what the first engineers said, there isnt much to service on these heaters
  10. nicholas Veitch

    nicholas Veitch New Member

    one more question this is the reset button yes ?

    File 17-01-2019, 19 34 20.jpeg
  11. bacon_sandwich

    bacon_sandwich GSR

    Well, not really, depends when it was last serviced, if never, then its a strip down of the bits that get clogged up. A full strip down is a couple of hours work. Then its testing to ensure it is running efficiently and all the safety systems work properly.
    If when it is cold and you press reset , if nothing happens, this can be a number of faults on the pre-ignition stages, you need test equipment to work out what is not doing what it should, i use my ears unless the site is really noisy, then i have to get my electrical tester out.
  12. bacon_sandwich

    bacon_sandwich GSR

    err, thats not the reset button i was referring to, its a user reset button front panel bottom right, take a photo of that area of the heater. That is the main safety stats, they should not need to be reset and if they do, please dont run the heater until it is fixed as you could loose the heat exchanger and then its scrap.
  13. nicholas Veitch

    nicholas Veitch New Member

    Okay thanks chaps. I will call the experts I wasn’t sure if I needed a commercial plumber or a spark lol.

    To be cold tonight, brr no heat tomorrow :(