BAXI HT380 intermittent hot water

Discussion in 'Plumbing and Central Heating' started by rad33, 6 Jul 2019.

  1. rad33

    rad33

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    Greetings from Canada!

    Hot water has been a pain for the last 2 weeks, started as hot water will turn cold mid-shower but will recover. Has been getting worse with hot water cycling 3x in about 10 minutes. I took a shower today and hot water was good for about 2 minutes and it turned cold, I had to cycle the shower faucet on/off to recover and will turn cold again. I can manage but the girls are not happy. I'm expecting to totally have no hot water in the next day or so. No fault codes.

    I called a tech but he isn't familiar with this boiler. I cleaned the NTC sensor the other day but it didn't help.

    Today, I found a video on how to test the hall effect sensor with a magnet. The only magnet I could find is from a screwdriver and it didn't light up (maybe magnet too weak). I'll get a stronger magnet from my toolbox at work and hopefully will confirm fault.

    For the meantime, can someone provide me the voltages for the NTC sensor and the hall effect sensor? Is there a proper wiring diagram I can get (not the one form the cover)? I will try to troubleshoot some more tomorrow.

    Thanks!
     
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  3. ianmcd

    ianmcd

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  4. bernardgreen

    bernardgreen

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    A Hall effect sensor requires a power supply to power the circuitry that detects the magnetic flux the sensor is tasked with detecting and/or measuring.

    A typical Hall effect sensor is HERE . ( not the one fitted in the boiler )
     
  5. ianmcd

    ianmcd

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    I know exactly how a Hall effect sensor works and was simplifying how to test one for the OP, so go on then genius, you explain to the OP how how to test it without a magnet
     
  6. bernardgreen

    bernardgreen

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    Is that a test with or without supply, and is the output from the particular Hall effect sensor a) binary. b) pulse rate or c) analogue output.

    a) flow / no flow
    b) pulse rate indicates flow rate
    c) output voltage indicates flow rate

    An accurate test of the sensor chip would require the use of a calibrated flux source.
     
  7. ianmcd

    ianmcd

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    you are the expert you tell the OP how to do it, I dont need telling
     
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  8. bernardgreen

    bernardgreen

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    I have no idea how to test that particular sensor.

    My point was that you provided incorrect "advice" when you said the Hall effect sensor "didn't have any voltage" and was "just a magnet".
     
  9. ianmcd

    ianmcd

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    Exactly so crawl back into your Troll hole and google the boiler
     
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  11. bernardgreen

    bernardgreen

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    Whatever you say the sensor does need a supply.
     
  12. ianmcd

    ianmcd

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    When a person comes on here asking for help, why do you not just try and advise them ( I know you havent a clue but try and be nice) instead of trying to appear as some know it all and spout absolute rubbish that is of absolutely no help to the OP asking the question, I get it that you are lonely and seek attention but there are sites for that, I could fix the OPs boiler in minutes , you google shoite and then pretend to be a know all, you are not a boiler expert, I am, you are not a heating engineer, neither am I , you are not a plumber, neither am I, I know what I am expert in, you however think that you are an expert in everything because you have google, guess what Bennyboy, Goggle is full of wannabees like you all quoting each other and you all believe everything because its on tinternet so must be fact
     
  13. rad33

    rad33

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    Yes, it is the Luna HT380.

    I was a able to test the hall effect sensor with a better magnet and confirmed that it is working. I then removed the flow sensor and can tell that it is the original and the filter is cracked. I cleaned it and reinstalled but no progress.

    Before I removed the flow sensor I can see that it would intermittently light up while in use but now it is pretty much dead and no hot water. I removed it and put my magnet close to it while someone is in the shower for the hot water and it works great.

    Is it safe to assume that the flow sensor is the culprit?
     
  14. ianmcd

    ianmcd

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    yes does sound like it , sometimes they can be cleaned out but ultimately best if replaced
     
  15. rad33

    rad33

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    Flow sensor came in the other day and it fixed my problem.

    For those who may come in later on and might have the same problem, this video will show how to test the hall effect sensor;


    Through that video I learned that you can make hot water if you put a magnet close to it. So for about a week someone was by the boiler with a magnet while someone was in the shower or doing the dishes. You will need a strong magnet. It was a pain but we survived.

    To remove the flow sensor you will need an 18mm socket and a ratcheting wrench. A spanner will work but a ratchet will work better because it's a little tight around the sensor. I referred to this video for removing the flow sensor;
    He said to clean it and you can use it again. Mine is 10 years old and I don't think cleaning it will get it better so I just chucked it out. It's a 15 minute job.

    I would advise others to read, read, read and watch YT videos as some of them are really helpful. It might not be your specific boiler but it might give you an idea how things work and where the parts are located. Another good video for reference;
    Not my boiler but pretty much the same.

    With this boiler, it seems that the NTC sensor can go bad and will not give you hot water. If you have to order parts, I'd say, order that as well so you have a spare.
     
    Last edited: 17 Jul 2019
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  16. ianmcd

    ianmcd

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    yet another post where the OP gets the correct advice and Bennyboy does his best to make him self out to be a smart arseee and completely wrong again, but where is he ? at a J&S convention ?
     
  17. bernardgreen

    bernardgreen

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    A Hall effect sensor is not "just a magnet". It is a semi-conductor integrated device ( a chip ) which produces a voltage that is related to the strength of the magnetic flux around the chip.

    In the boiler's flow sensor module the flowing water forces a magnet upwards and thus closer to the Hall effect chip, this increases the magnetic flux around the Hall effect chip and the output voltage from the chip increases. A comparator circuit compares the voltage from the Hall effect chip with a preset level. If the voltage from the Hall effect chip is higher than the preset level the comparator circuit gives an active output to the boiler's control system ( the PCB ) and also lights the LED. ( The comparator circuit, also semi-conductor may be fabricated on the same silicon as the Hall effect sensor chip.

    You probably know how the Hall effect chip works but for other readers who may be interested. Re-drawn from very old notes.

    Hall effect chip redrawn 2019.jpg

    A voltage source drives a calibrated current across a plate of semi-conductor material. When there is a magnet field the motor effect (*) causes some electrons to follow a curved path and some of these reach the sense electrode(s).

    (*) motor effect is that a wire carrying current in a magnetic field will try to move. It is the elecrons in the wire that make the wire try to move.

    Who is the un-smart who stated a Hall effect sensor does not have any voltage......? Oh yes it was this guy

    Of course the sensor in this boiler might be a simple reed switch with no Hall effect device involved. I do believe it is a Hall effect sensor as a reed switch would have to be very sensitive to be operated by a magnet inside a pipe several millimetres from the switch.

    who was designing equipment using Hall effect devices in the 1970's
     
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