Intermittent Hot Water - Baxi 105e

Discussion in 'Plumbers' Talk' started by MFC, Sep 18, 2007.

  1. MFC

    MFC New Member

    I've got a fault on a Baxi boiler where the hot water either doesn't heat or if it does it is only for a few seconds then goes cold again. It seems to work fine when the CH is on.

    A fault light appears under the 70 degree indicator and looking at the manual (which may as well be written in Russian) I'm led to believe it's the Hot Water Temperature Sensor.

    From looking at other threads it seems to be a common problem but not a definitive or simple answer. I am worried that if I simply call a plumber I will be charged for all sorts of parts that I don't need. Therefore, would someone be able to advise on the likely solutions and if there is more than one option then a guide price for fixing this.

    If there are any plumbers in the Doncaster area that are interested in taking a look let me know!
  2. T482 

    T482  New Member

    try renewing the DHW diaphragm..if not, change the diverter valve
  3. Dreadnaught Heating

    Dreadnaught Heating New Member

    Try T482's answer, but I suspect blockage (partial) in heat exchanger, causing high limit stat to operate, as it cools it fires up again.

    You could contact HeatTeam (BAXI/Pottertons service arm for a 'fixed price' cure)

    Please, do let us know what is eventual cause, and the cure. (And, if you're feeling adventerous how much it cost to cure it)

    Patrick
  4. new to here

    new to here New Member

    I would think its over heating not diaphram or div valve.
  5. plummit

    plummit New Member

    Have had the baxi 80 e trip out on "overheat",. When this has happened no dhw or ch.
    reset the over heat switch and all seems well.
    Numerous reasons for this, sludge, pump, powerloss etc etc. Please post back the fault if you would.
  6. MFC

    MFC New Member

    Thanks for your help guys - will let you know the outcome.

    Went on the HeatTeam website but no indication of the fixed cost. Are they as bad as BG and use this as an opportunity to say I need a new boiler - it's only 4 years old but you hear these things!

    A bit more info that may be causing the fault is that I had a leak on one of four radiators the boiler runs a few months ago. An emergency plumber disconnected and drained the radiator and what with not needing the CH on I've not got round to replacing the thermostatic valve. Could this be causing the problem???
  7. new to here

    new to here New Member

    Sorry really daft question but the system is refilled isn't it
  8. Tony Soprano

    Tony Soprano New Member

    i had the same sort of problem intermittent hot water,turned out to be the secondary heat exchanger which was slightly blocked replaced and boilers b een running fine since
  9. myzeneye

    myzeneye New Member

    i look at these things in this order....

    diverter valve diaphragm.
    dhw micro switch.
    dhw thermistor.
    temp checks on inlet and outlet of the secondary heat ex looking for blockage.


    lets us know what it is.
  10. MFC

    MFC New Member

    Don't worry about daft questions - sometimes that leads to the solution!!!

    But, yes, it is refilled.
  11. chris73

    chris73 New Member

    I`v had a couple of these , try the hw thermistor , about £12.00 and an easy job .

    once again lets us know .
    chris
  12. MFC

    MFC New Member

    Just to keep those that wanted updating, updated:

    I've checked the Diaphragm, which appears to be ok, but changed this anyway to make sure. This hasn't solved the problem unfortunately. What is happening though is the microswitch located behing the diaphragm that controls the burner is flicking up and staying up when the heating is on, but as soon as water is turned on from the kitchen tap it drops, therefore cutting out the burner.

    Also, which is quite puzzling, the flashing fault light at the 70 degree indicator remains on even when the boiler has been turned off and then turned on again and there is no water running.

    Logic is leading me to believe that it is the thermistor as there is obviously something to do with the temperature that is cutting out the burner on DHW.

    Am I on the right track?
  13. Bigdave23

    Bigdave23 New Member

    Hi, I had a similar thing but with the central heating sensor showing a fault. My advice would be to change the hot water thermister, should cost less than £20 to buy and is easy to fit, so not a great loss if it does not work. Changed mine and has been fine ever since. plaese let us know how you get on.
  14. myzeneye

    myzeneye New Member

    does the dhw resume normal operation after manually reseting?
    also, the micro switch should close and the other dhw one should operate in exchange...thats normal..

    i went to look at a 105e yesterday with a similar problem..... intermitent dhw....

    problem is no dhw.
    c.h operation is fine.
    a dhw demand during c.h operation interupts as normal ( but with no pump, fan, or burner)when dhw demand ceases, c.h operation resumes as normal....

    divertor diaphragm has recently been replaced (so im told)....
    upon dhw demand, the divertor is moving and the push rod is operating the dhw micro switch....(small tap led symbol lights up on display as it should)
    manual says pump should be next, but nothing. dhw micro swith clicking over is the last thing it does.... manual also says "pump fault" led should blink.... but it doesn't....i tested for 230V at pump upon demand, but nothing. next i tried for 230V on pcb connector A4,terminals 3&6.... no voltage.
    so, book says its the pcb, but as the pump fault led isn't flashing as it says it should be im a bit reluctant to dive in and point the finger at the pcb....(cost...)

    went and had another look tonight...
    damn thing was working fine.
    changed a kitchen tap for them whilst i was there, then tried dhw again afterwards...it worked fine at first then the dhw got very/steaming hot.... felt pump, it was still running, then burner went out and the 70' led started flashing....dhw was then inop from this point...but c.h was fine.
    so i got the meter out an tried a few things..
    no 240V at pcb connector A4 terms 3&6 (pump L)
    drained dhw side and removed dhw sensor.... couldnt find correct ohmage rates in manual for it but noted that when dipped in hot water the resistance got higher( as it should be)
    refitted, and the boiler fired up fine for dhw demand!!!
    so, not sure if it was as a result of haveing the mains power turned of or fiddling with the dhw thermistor , or simply the pcb had got over its issues.....

    im guessing that as the operation is fine for c.h even when dhw operation is out, that rules out a faulty high limit stat. and the fact that manually resetting didnt help.
    i made sure the modureg was working right too, it was and all seemed in order.
    so im guessing its got to be either a wonky dhw sensor or the pcb...
    the question is, would a faulty dhw therm cause the live feed from the board to the pump to fail ?
    id have tought the last thing the boiler wants in an overheat situation is the pump to stop, so im guessing no it shouldnt.... therefore the prob must be the pcb....

    can anyone agree here or point out where im wrong...
    thanks guys
  15. MFC

    MFC New Member

    And the result is....

    ...the thermistor!

    Easily changed and didn't cost a lot as it was relatively easy to fit!

    Thanks for the advice guys ;)
  16. myzeneye

    myzeneye New Member

    well done old son.
    thermisters can cause all manor of mayhem.
    for future referance, an ntc thermister should give a reading of a drop in resistance as temp increases.... this can be achieved by removing it and dipping it in a cup of hot water whist fiddling with your multi meter ...

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