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Myson Maxton Electric Boiler (model MB12)

Discussion in 'Plumbing and Central Heating' started by whizzywig, 16 Nov 2020.

  1. whizzywig

    whizzywig

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    Hi. I’m a newbie here.

    My heating setup since 1982:
    • 170 litre vented indirect hot-water cylinder (Economy 7)
    • 24Kw wood burner (the main heater), for hot water supply and for heating radiators
    • 12Kw Myson Maxton Electric Boiler (model MB12), for supplementary heating of radiators alone or in tandem with the wood burner

    Problem:

    The Maxton thermostat control seems to function only as an on-off switch, with no variable control and the neon indicator doesn’t light up, so I suspect the boiler is working on an all-or-nothing basis.

    I’ve been reluctant to use the electric boiler even at the low rate, but wood fuel prices have been increasing so much over the last few years and I’m looking to get the electric boiler thermostat sorted out so that the modulated function can be used more efficiently.

    • Does anyone have experience of the Maxton?
    • I’d really like some advice re sourcing replacement parts please. I’ve previously asked an electrician to look at it, but he just threw his hands up in the air!
    Any advice would be very welcome.

    Thanks.

    Jerry H
     
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  3. ianmcd

    ianmcd

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    Your boiler will have 4 x 3KW heater elements, as the return water heats up the boiler switches off an element at a time, when the water cools down the boiler brings on how many elements it needs, this is all done automatically by the boiler, you cant alter how this happens by any external controller
     
  4. whizzywig

    whizzywig

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    Hi Ian,

    Thanks for the quick reply! I can’t believe that I’ve had the Maxton for 38 years without realising that it has four elements ..... :eek:

    ... so, ... after checking it out I take it that the Maxton is a form of modulating electric boiler?
    • The boiler is in the airing cupboard upstairs together with the hot water cylinder and a small heat leak radiator.
    • All the radiators (they have their own thermostats) are downstairs, except for two heated towel rails upstairs.
    • the original downstairs room thermostat is useless as it is in a cool and draughty hall, but enables remotely switching off the upstairs boiler if not required.
    • one towel rail was rejigged as a secondary heat leak when our wood burner was replaced about six years back as the fitter said that the original small heat leak was under spec.
    Regarding the apparent non-functioning thermostat knob, I’d like to know whether replacing it (and the duff neon indicator) would help fine tune the output control? Might it’s non-functioning be compromising the automatic modulation?

    This tandem system works very well despite never having been serviced.

    Occasionally I release the auto air vent and clean the screw cap (which rarely has had any significant concretions; and neither do I see any beads of water there any more).

    And as it’s an open vent setup there is no pressurising of the system, so I’ve always assumed no drips from the auto air vent is OK - but should I have that replaced?

    Many thanks again, in anticipation.
    Jerry H
     
    Last edited: 18 Nov 2020
  5. ianmcd

    ianmcd

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    What do you mean by non-functioning thermostsat knob ?
     
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  7. whizzywig

    whizzywig

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    21C4C7FC-830B-4655-9A42-B1793323F202.png


    Sorry. I was referring to the ‘control thermostat knob’ (larger diagram, top right of attachment) or the ‘thermostat control’ (smaller diagram, bottom left). It now only serves as an on/off switch, with no other function apparent, whether set at 1,3,6,9 or whatever o’clock.
    I’m pretty sure it originally served to adjust the desired temperature.
     
    Last edited: 20 Nov 2020
  8. ianmcd

    ianmcd

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    My apologies, I was thinking of a different boiler, yours only has two elements which is very unusual, yes your thermostat should adjust desired tempersture, but possibly does this by just an on off control, not designed to be turned up and down all the time, but set to whatever temp you require then the on off times set by an external controller thermostat or timeclock
     
  9. whizzywig

    whizzywig

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    ...... possibly does this by just an on off control, not designed to be turned up and down all the time, but set to whatever temp you require then the on off times set by an external controller thermostat or timeclock .....


    Thanks for your input Ian,

    I think it has to be a manual control as the ‘control thermostat knob’ has a Stop and Min>Max dial on the face panel. There certainly isn’t any min or max function at present, just off or on. And the on/off times are set on an adjacent timeclock.
    The fuses appear intact. So I guess I’m looking for the thermostat and neon light to be replaced.
     

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  10. ianmcd

    ianmcd

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    The neon light simply tells you that the elements are heating and will go out when the temperature is reached, it has no affect whatsoever on the efficiency or operation of anything else
     
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