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24ci hot water or heating but not both (F19 error)

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  • 24ci hot water or heating but not both (F19 error)

    For my sins, I have a 24ci which was installed in the cellar below the level of all the rads so it gets all the debris :-( The engineer (friend of a friend) came because the expansion vessel had gone, which he reckons was due to overfilling after the pressure sensor got clogged. Anyway, he fitted an external expansion vessel for me and cleaned out the sensor. It fired up but as soon as you draw any amount of hot water, it throws an F19 (NTC not connected). If CH is off, the hot water works for a while then goes to warm. It seems if you turn of the water then back on it starts to warm up again. If the CH is on, you get an F19 within a few secs with the HW tap full on. He said that points to some kind of thermistor fault or the pcb.

    He didn't have the right thermistor on the van so tried one from, I think, a Vaillant. I have no idea if this is still 10kOhm like the original part; anyway, same problem. To save the cost of another call out, he suggested I fit a new thermistor 1st as it's cheaper and if that doesn't work the next thing to try is the more expensive pcb. If both thermistors give the same fault, can you think of any reason a new one would be any better? Is there anything else to try? Given that there are new pcbs on eBay for around 65, is it worth going straight for that or even buy another 24ci for spares (a bit of a lottery, I appreciate)?

    He advises fitting a Magnaclean to mop up the crud which is causing havoc with the system. Makes sense to me.

    I'd be grateful for qualified opinion.

  • #2
    check you have continuity on the wires!!!
    Also, if its getting hot then warm, is it passing the diverter?
    are the thermisters clean? (you say the system is dirty)
    are they giving out the right readings?
    IS the heating working fine? if so plate to plate? (dirty system)
    if its a Ci then it must be a few years old now!!! You may want to start setting some money aside for a replacement.
    With funny faults like that, iyou can end up spending half a day tracing faults and end up fitting a 15 part but have a bill of 200 labour!!!


    • #3
      Many thanks. Not sure what the readings should be but do have a test meter. Yes, CH works fine as long as you don't run DHW with it on or it shuts down. The DHW is erratic with CH off. Ran a nice hot bath, yesterday but had to turn the shower on and off a few times to maintain heat yet my partner had no probs with her shower. My plan is to fit the Magnaclean and see what it catches, then take it from there. Sounds reasonable?


      • #4
        What temp is your hot water set to? turn it down!!! believe it or not it can be a simple thing!!! If the boiler is scaled or clogged, the boiler may not be able to clear the heat quick enough! so turn the temp down!!!!!


        • #5
          It's on max. Thanks will try