Home  5  Books  5  GBEzine  5  News  5  HelpDesk  5  Register  5  GreenBuilding.co.uk
Not signed in (Sign In)

Categories



Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.
Buy individually or both books together. Delivery is free!


powered by Surfing Waves




Vanilla 1.0.3 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to new Forum Visitors
 Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications: Apply now.




General: MVHR overheating warning

Bottom of Page

1 to 30 of 40

  1. <
  2. 1
  3. 2
  4. >
    • CommentAuthorRex
    • CommentTimeApr 8th 2023 edited
     
    What ho one and all,

    I have a Flexit (Helios?) L4X HVMR unit which I installed when I built my house, around 12 years ago. I change the filters regularly; it runs around 8 hours per day over three different time periods. The last period is the late evening and I press the central button on the control panel for a 30 min high speed boost to remove moist air from the bathroom.

    It is connected to the UFH pipework so when the UFH is on, there is a bit of pre-heating of the incoming air.

    Recently, too frequently, I seen the panel (image below) with the red warning LED (top) illuminated. According to the instructions, this is an overheating thermostat warning light when the unit starts. The solution is in the loft, (very inconvenient following a both!) press the 'Reset' button. Usually, I also unplug before resetting.

    Back at the control panel, sometimes pressing the two temp buttons (left and right buttons) simultaneously is necessary, but the unit then starts and works fine.

    There are only two thermostats that I am aware of; one on the supply side, after the unit to measure the air temp and one within the heat exchanger. I have cleaned both.

    My problem is that I have no idea what overheating thermostat actually means, where to find it and how to cure the issue.

    Grateful for some advice.

    Many thanks and toodle pip

    The photo show the panel in warning' mode. The left/right -/+ set the temp, which with both red lights on, is 20C as need to reset via this panel. The C light is sometime on and sometime not; don't really know what it is telling me!
      Flexit Panel (Small).jpg
    •  
      CommentAuthordjh
    • CommentTimeApr 8th 2023 edited
     
    Ask the supplier/manufacturer if it isn't clear in the manual?

    edit: presumably your UFH connection is actually a post heater? In which case is the thermostat before/after/within it? Is the UFH on? i.e. could the problem be hot water flowing around when there's no airflow.
    • CommentAuthorRex
    • CommentTimeApr 8th 2023
     
    The supplier were kinda useless and have gone out of business. They would not listen to me and designed a system of ducts that went through a steel beam that supports the floor. Neither the plans, photos and a video made any difference, that is what they designed!!!! Of course, did not know how useless they were when I gave them the job.

    Yes, the heater 'battery' is on the exit side of the unit and the thermostat is about one foot further along the supply duct. The UFH is currently on, but it is weather compensated so at the moment, does not actually fire up. And if it is running, the max flow temp is around 38C; never been a problem in the past so don't know why it would be now.

    I have sent an e-mail to the Swedish manufacturer but after ten days and no response, wonder if I am being ignored.
    • CommentAuthorMike1
    • CommentTimeApr 8th 2023
     
    Posted By: RexI have sent an e-mail to the Swedish manufacturer
    Have you got the correct manufacturer? Looks like they could be Finnish?
    https://www.onninen.fi/en/onnline-control-panel-energy/p/AHN331
    • CommentAuthorRex
    • CommentTimeApr 9th 2023
     
    Yes, have the correct manufacturer.

    https://www.flexit.no/en/products/air_handling_units_300-700_m-h/expired_models_automatic_300-700/control_panel_ci50/

    Yesterday afternoon, not having reset anything, the unit came on and was running as it should. It them goes off for a few hours, coming on again at 22:00. At 22:00, it should overload mode again.

    This morning, again, overload mode; went into the loft and reset the unit, then the -/+ temp control to reset the panel (or whatever doing that resets) and the unit is working as it should.

    The external and internal temps are such that the UFH has not come on.
    •  
      CommentAuthordjh
    • CommentTimeApr 9th 2023
     
    Posted By: Mike1
    Posted By: RexI have sent an e-mail to the Swedish manufacturer
    Have you got the correct manufacturer? Looks like they could be Finnish?
    https://www.onninen.fi/en/onnline-control-panel-energy/p/AHN331
    Certainly that looks like the control panel. The MVHR manufacturer is apparently Norwegian, with a Swedish factory, according to https://www.flexit.no/en/about-flexit/about-us/ and an American domain for email export@flexit.com !
    • CommentAuthorRex
    • CommentTimeApr 9th 2023
     
    Thanks. May be I will give them a call although I am still awaiting a response to my e-mail at that address.
    • CommentAuthorRex
    • CommentTimeApr 12th 2023
     
    Have made some progress in speaking with the Flexit people in Norway. Seems there are two overheating thermostat on the incoming air side and one or both may need replacing. Fortunately, parts are available.

    Did a Dr. Google search to see how to test these things, ans appears that if thee is continuity, all should be OK.

    Thermostat in the photo is the rest button (which probably only has around 0.5mm of movement IF in the raised position) and I get a continuity sign from it.

    The other (to the left of the photo) does not have the button, and there is no continuity. Presumably, it is therefore not working? If that is the case, why when the MHVR fires up with the warning light, and I go to the loft to reset the button, the unit then runs fine if this stat is not working?

    Is it a wise assumption that this stat is faulty, always open and should be replaced?
      Reset (Small).jpg
    • CommentAuthorGreenPaddy
    • CommentTimeApr 13th 2023
     
    Rex, difficult to be certain without spending time researching the sensors/control philosophy of the system, but I would work on the following basis:

    - it appears the sensor isn't "just" a temperature probe (like a PT100 or some sort of resistance probe). It is a fail-open type of stat, which requires manual intervention to re-set. A simple temp probe would be tested by checking the resistance over its range (ice water, boiling water etc) and comparing with the manuf's table of resistance versus temp.
    - I'd guess that there are two sensors, one that measures temperature, and the second (with the reset) which is the fail safe control trip. As above, two different pieces of kit.
    - assuming there is no excess heat input to cause a "true" overheat scenario, the problem is that the temp stat "trips" at the wrong temperature, ie. it's faulty.
    - I imagine the stat will be maybe £20. I'd order a new one and just replace it. That's the only way you'll know if it is the stat, or some other issue. If the manuf wants a silly price for the stat, you can likely study the details of the stat, and buy an identical off 'tinternet. The MVHR manuf will have bought the stat from a stat manuf, just as you can.
    • CommentAuthorRex
    • CommentTimeApr 13th 2023
     
    Thanks for your reply.

    Have made a bit of progress in my understanding. Not sure I understand why the overheating / reset stat is on the incoming air flow, but having removed it, shaken it a bit and wiped the base with a damp rag, for the past 24 hrs, everything is working as it should.

    Regarding the other, non-resetable stat, I now believe that to prevent the unit from freezing so obviously only works if the incoming temp is very cold, and as a result, activates the electrical pre-heater. Obviously, in normal conditions, it would be open, which it is.

    Replacement stats are available from Sweden/Norway, but will continue to monitor before replacing.

    Thanks everyone for your thoughts.
  11.  
    Does the system have an electrical pre heater fitted and connected?

    If so, the stat has an important safety function and you should replace it. It is there to stop the electrical heater running if the airflow became insufficient to carry away the heat, for any reason (blockage, fan failed) and so causing overheating/damage/fire. It is purposely made difficult to reset so that people will investigate the safety fault rather than just resetting the sensor.

    If replacing the stat doesn't stop it tripping, then there is a safety problem with the preheater.
  12.  
    Posted By: RexReplacement stats are available from Sweden/Norway, but will continue to monitor before replacing.

    Posted By: GreenPaddyThe MVHR manuf will have bought the stat from a stat manuf, just as you can.

    Components often have an identification number printed on them and a google search on that number can give a few options for sourcing the component - which allows you to order at the best price / convenience.
    • CommentAuthorRex
    • CommentTimeApr 13th 2023
     
    Agreed. I was only searching for the Flexit part rather than whatever is printed on the stat itself.

    Will have another look, although that does entail removing it again.
    • CommentAuthorRex
    • CommentTimeApr 14th 2023
     
    There is so much printed data on the side of the stat that I am unable to determine the part number. However, a Google search and I did find some that look similar, with a price not significantly different from buying a Flexit part.

    However, in the past 24 hrs, there have been four on/off cycles and no overheating warnings. Have not done anything specific to fix the stat so time will tell.
  15.  
    While you have it out, put it in the cold kitchen oven. Turn the oven on to its lowest setting so it slowly warms up. Every minute, measure the oven temperature with a thermometer and check if the stat has tripped yet. Stop when it does, and note the final temperature

    You can use this info: a) to check if the stat is tripping at a sensible temperature or if the fault lies elsewhere, and b) to search for an equivalent stat.

    (And - obviously - stop before anything melts!)
    • CommentAuthorMike1
    • CommentTimeApr 15th 2023
     
    Personally I'd buy 2 stats. If only one needs replacing you have a spare in case / for when the other goes.
  17.  
    12 years is a long time to have a spare siting on the shelf (12 years being the life of the original)
    • CommentAuthorRex
    • CommentTimeMay 27th 2023 edited
     
    What ho one and all,

    Some progress but.... Email to Sweden for a replacement stat and informed they will not ship the part to the UK.

    It is a 16/250AV Normally Closed 80C, manual rest stat but the base has a smooth shape that allows it to fit flush into the incoming air flow.

    However, I have found many that will fit but they all have a base which will not fit flush in the hole, although the stat will fit in my MCHR unit as the bracket dimensions are the same.

    The second photo is a typical example of what I have found on the net.

    First question; why does all my Google searching only find stats that look like that second photo? Cannot find anything that resembles my current stat base. As the second will fit but the face will not protrude into the air flow, am I likely to encounter any difficulties?

    Secondly, it appears that the most common stat is 10/250AC but my current is 16/250AC. What happens if I fit a 10/250AC?

    Third photo is the current stat. Where can I find a stat like the existing one?

    Thanks and toodle pip
      20230526_141316 (Medium).jpg
      2023-05-27_100032.jpg
      20230526_141144 (Medium).jpg
    • CommentAuthorMike1
    • CommentTimeMay 27th 2023 edited
     
    Posted By: RexCannot find anything that resembles my current stat base. As the second will fit but the face will not protrude into the air flow, am I likely to encounter any difficulties?
    I can't imagine that a 2mm projection would make a great deal of difference. However I can see a couple of stats that do project - the Fagor Brandt 283311AAC and 95X0080 (may be the same product) - which I assume are normally closed as they're also safety thermostats, but not sure what their dimensions are. For example https://spares2repair.co.uk/fixed-value-thermostat-limiter-safety-80o-fagor-brandt (available for ¼ of that price in Europe). Zooming in that looks like 16A 250V AC too, though that may be a 4 in brackets on the Ampage?

    Posted By: Rexthe most common stat is 10/250AC but my current is 16/250AC.
    That will be 16A 25V AC current, the maximum it can safely handle

    Posted By: RexWhat happens if I fit a 10/250AC?
    If your HVMR unit is running at 230V and protected by a breaker of 10A maximum (I'd guess it may be 2A?), it should be fine.
    • CommentAuthorRex
    • CommentTimeJun 2nd 2023 edited
     
    I have not yet ordered a replacement stat, as I am not convinced that the manual reset stat is faulty.

    For the past week, the MVHR unit has started just fine, including in the morning when the outside temp is cooler. Until this morning!!!! when the alarm red light was on. Resetting on the control panel does nothing, until I have rest on the manual rest stat.

    However, before resetting the stat, although I disconnected the two terminals (have to to that to get access to the connectors) and took a continuity reading. It should be closed and it was. I then applied a bit of heat to its base with a hair dryer and sure enough, it opened. So perhaps it is working?

    But this is what I don't understand. On the air inlet, there is an electrical pre-heater, then the two stats (one 16/250V, N/C, manual reset, apparently set to 80C. The other with no rest and I am not sure what it does) before the inlet filter. When the unit goes into alarm mode, disconnecting the manual reset stat for a few seconds / wiggling the reset button, and resetting with the buttons on the control panel, and all is fine.

    Given that the 80C stat is presumably to prevent 'hot' intake air getting too hot (but 80C is hotter than the average sauna!) and the stat is normally closed and seems to be working, why would it be causing an 'alarm' when a/ the pre-heat is not working and b/ there is no way the incoming outside air is anything other than cool?

    What would happen if I disconnect both pre-heat element and the incoming N/C (possibly faulty?) stat?

    I'm not sure if the pre-heater has ever worked as here in leafy Surrey, we do not get below freezing temps very often.
  21.  
    Posted By: WillInAberdeen While you have it out, put it in the cold kitchen oven. Turn the oven on to its lowest setting so it slowly warms up. Every minute, measure the oven temperature with a thermometer and check if the stat has tripped yet. Stop when it does, and note the final temperature

    You can use this info: a) to check if the stat is tripping at a sensible temperature or **if the fault lies elsewhere**, and b) to search for an equivalent stat.

    (And - obviously - stop before anything melts!)
    The 80⁰ safety stat is there to prevent a fire/meltdown if the fan airflow ever got blocked/stopped whilst the heater was energised. The other stat is the everyday on/off control that decides if heating is required today depending on the weather, test it in your freezer. There is no guarantee that either one still works at the original specified temperature, until you test...!

    If you are considering disconnecting the safety stat , you need to be 1000% sure the heater is disconnected first, and label it all up or cut the terminals off so no future trades/owners reconnect it without the safety stat in place. The 'alarm' might go permanently on.



    Even if not needed for heating the house, the preheater is possibly also intended to stop the heatexchanger condensation from freezing onto the fan on frosty mornings and unbalancing it (even in Surrey). Other models handle this problem by stopping working on frosty mornings, or by having bulletproof fans located on the warm side.

    The safety stat should physically disconnect the heater (in series, breaks the circuit) and the control unit should notice that the circuit is broken and put the red light on. Could something else be breaking the circuit and causing the alarm to be logged, eg intermittent dodgy connection in wiring, or heater element burned out? Check continuity all round the circuit.
    •  
      CommentAuthordjh
    • CommentTimeJun 2nd 2023
     
    Posted By: WillInAberdeenEven if not needed for heating the house, the preheater
    Preheaters can never heat the house, because their heat is immediately exchanged with the outgoing air! They are, as you say, to eliminate the possibility of condensation freezing within the MVHR unit, either within the heat exchanger or possibly on the fans or ducts. PH-certified MVHR units are required to use pre-heating rather than varying the ventilation rates. A post heater can be used to heat the house.
  23.  
    Indeed, but I didn't intend to explain that here! Rex feels that he doesn't need it to heat his house in Surrey, and I am not going to argue...

    But I suspect that the heater is still being used for defrosting. Rex is happy to switch the unit off many hours of the day (PH notwithstanding) which would be a more energy efficient way to cope with frosty mornings.
    • CommentAuthorRex
    • CommentTimeJun 4th 2023
     
    I was just asking; not planning to disconnect anything. Sorry to hark on about this rather trivial but very annoying issue.

    The alarm warning seems to be somewhat random. Sometimes it is on and the unit will not run; other times, both he alarm and element heating light are on. Most times when starting, it runs just fine.

    Given that the outside temp is certainly not below freezing, why would the pre-heat element be active? Since I am not in-front of the panel when the power comes on, it could be that the pre-element heats up, and causes the stat to open, hence the alarm and non-running until reset.

    In which case, what can I do to 'test' the pre-heat element? If I check it now, it will show continuity. But something could be causing it to activate even on summer mornings. Having said that, the panel displayed an alarm light last night!
  25.  
    Remove both stats and test what temp they operate at? If the control stat has drifted and is switching the heater on at 12⁰ instead of 2⁰, it will create the effect you described, the element light being on supports this idea. Or if the safety stat has started operating at 40⁰ instead of 80⁰. Look out for if any of the terminals are loose.

    It is worth persisting with this, problems with the safety overheat on electric heaters need to get bottomed out, don't want a fire! If a red warning light kept coming on on a car, we wouldn't keep resetting it and driving on... (ahem).
    • CommentAuthorRex
    • CommentTimeJun 4th 2023
     
    "If a red warning light kept coming on on a car, we wouldn't keep resetting it and driving on"

    Extremely good point.
    • CommentAuthorRex
    • CommentTimeJun 16th 2023
     
    Sometimes the HVHR unit works, sometimes the alarm light is on. Resetting the manual rest on the stat then resetting the reset buttons on the panel, and it all works again.

    I am assuming that something like this

    https://sinolec.co.uk/en/manual-reset-thermostat/1211154-thermostat-80-closed.html

    will be the cure? Is there any reason that I should not try this?

    Thanks
    • CommentAuthorCWatters
    • CommentTimeJun 20th 2023
     
    Possibly a loose electrical connection between the overheat stat and the control unit. If this goes open circuit it looks like an overheat alarm to the control unit.
    • CommentAuthorMike1
    • CommentTimeJun 20th 2023 edited
     
    Posted By: RexI am assuming that something like this
    manual-reset-thermostat/1211154-thermostat-80-closed.html

    The specification looks OK to me, and the price is very affordable.

    Though, as CWatters says, it could be a loose connection.
    • CommentAuthorRex
    • CommentTimeNov 26th 2023
     
    Back again with the same issue as it was not really a problem during the warmer summer months.

    However, now we are in the colder winter months, the alarm light is coming on more frequently. Seems to be that cold air on the inlet is triggering the n/c thermostat, but that really does not make sense to me.

    I have visually checked for a loose connection but nothing is obvious. Is there another way to check? The inlet chamber has an electrical pre-heater that I have never used, so the stats are obviously there to prevent overheating.

    I am wondering, could I take the pre-heater out of the circuit and so there cannot be an accidental future 'on' situation, and join the stat wires together to by-pass the stats?

    I have ordered a couple of new (Chinese?) stats but they will require a bit of adaption to actually mount to the MVHR unit. Not a big deal.

    With the recent alarm illuminated, turning the unit off, wiggling the manual reset, disconnecting and reconnecting the stat spade terminals, unit plugged in again and press the control panel reset buttons, and it usually fires up as it should.

    Don't know what is next?

1 to 30 of 40

  1. <
  2. 1
  3. 2
  4. >
   
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   
Logout    

© Green Building Press