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Worcester 28SI ii no heat or water after a short time..!!

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  • Worcester 28SI ii no heat or water after a short time..!!

    Hello to all,

    I've a worcester 28SI ii boiler that initially fires up when calling for CH.
    I've only at this point been asking for CH and not DHW.

    It then try's to regulate the flame which fluctuates up and down for a while and then goes into lockout.. This is probably about two or three minutes.

    Red light flashing 4 times per second.

    At this point the boiler obviously isn't going to fire until the reset is pressed to which I do.

    The boiler resets but then when it tries to fire again the boiler relay clicks over to pull the fan into operation but cuts out quickly almost like the fan won't start.
    I'll point out now that the fan is not ceased and is free to spin..!!! After all it has been running for a short time..!

    It's almost like it detects an overload to the fan and cuts the supply..
    It will try this a second time but then goes into the 4 flashes per second..

    Reading through the manual it says that it could be the CH or DHW sensor among a few more things but my question is this really, what are the sensor resistance values for the sensors to be deemed good and what are there values for them to be deemed faulty..?

    ie, what limits to there values will put the boiler into fault.
    I'm assuming that they are after all just thermistors.!!?

    I will reiterate that when the boiler is stone cold ie left over night that the boiler will fire up for a few minutes but after this short period of being on then it refuses to fire again.

    I've checked the ignition leads for being between 2000-3000 ohms and they are good, 2500 ohms on each lead.

    It just seems, like the sensors go that far out of values that the boiler refuses to start again until they've been left in a colder state for some considerable time.

    The code plug seems Ok but the only thing on the PCB are two small resistors by the look of them..
    What should there value be.?
    Measuring across them I get 1.5k on one of them and 3.5k on the other..
    What does the code plug signify too. I'm again assuming here that there's a code plug for LPG and one for natural gas..!!??

    Over temp cut out is also fine, wiring loom seems Ok too..
    The pressure switch is also good clicks loudly and makes good contact with a resistance meter.
    The flue isn't blocked either as it's only a short tube to the outside wall and is clear.
    From what I can see, the flame sensor is all intact but again, is there a resistance value for this sensor.??

    Im a little puzzled as to why it will fire up for a few minutes then cut out for so long afterwards though.. It seems to me that the sensors after being hot for only a short time refuse to play ball until they've been left cold for a while..

    Thanks for any help that anyone can supply me with.. Kindest, James.

  • #2
    Are you Gas Safe Registered?


    • #3
      Originally posted by albatross View Post
      Are you Gas Safe Registered?

      Just some more info on this boiler too.

      On initial firing up when the boiler fires up, the flame is on yet after a short period of time the ignition sequence comes into play even though the flame is lit and burning...
      The flame sort of starts to die down after a couple of attempts to maintain the burn..!!!

      Flame sensor problem..???? Poor reading of the sensor at the main board due to a knackered main board.

      Do these main boards fail regularly or are they pretty reliable.

      What I don't want is a service engineer coming around to my house and taking the piss by saying you need this that and the other parts mate and ripping me off.. Hence the Spanish Inquisition on here before I get someone around. A new flame sensor maybe 15 or they might just say I need a new boiler just cos they want the extra work and dough out of me..!!

      Thanks for a reply too.


      • #4
        I thought not. You have broken the law by even removing the case and many other times by other things you have done. You do not have the knowledge or equipment to verify the boiler is safe. Put the case back on. Turn the boiler off and turn the gas off. Pay a qualified engineer to repair it and stop being a prat before you injure or kill someone.

        And when the engineer comes do not try to tell him how to do his job, you will make yourself look stupid and annoy him, probably costing you more.


        • #5
          Don't put you're life at risk by trying to fix something you don't understand. Some will rip you off bit most are just trying to earn a living. As engineers we have high overhead costs to cover so that's why it might seem expensive.