Mega flow - no HW (with pics)

Discussion in 'Plumbers' Talk' started by Not Too Sure, Apr 11, 2021.

  1. Not Too Sure

    Not Too Sure Member

    Hi Gents

    I have the MEGAFLOW CL250 (landing upstairs) and have timers/controls downstairs next to my boiler to turn the central heating and hot water on and off.

    The central heating fires the boiler up and works fine, however the hot water switch is set to on but the boiler isn’t firing up as a result (despite the water being cold). I can use the immersion switch in the airing cupboard for now, but wondered if anyone could point to the issue ?

    I have 3 valves in the airing cupboard and moved all 3 to manual and yet the boiler still didn’t fire up (pics are before I set it to manual)? As I said central heating is working fine.

    Any ideas - picture of the set up below?





  2. andy48

    andy48 Screwfix Select

    There could be a number of things causing the symptoms you describe, including a faulty motorised valve, a faulty thermostat or an overheat thermostat which has tripped. As you have an unvented hot water cylinder, any work on it must be done by a G3 registered engineer, they are not DIY devices!.
    1. Setting motorised valves to "open" does not usually move the mechanism inside far enough to turn the microswitches to "on" and thus fire the boiler. They can only be tested by someone with the correct test equipment (multi-meter, proving device) and the experience to use them in the presence of mains electrical voltages.
    2. A faulty thermostat definitely needs a G3 registered engineer. There is no easy and safe way of testing them without appropriate equipment and experience.
    3. While the ordinary thermostat opens and close with varying temperatures, an overheat thermostat opens when a pre-determined high temperature is reached, and has to be manually reset, usually by depressing a small button, sometimes through a small hole. If you can find the overheat thermostat, try resetting it, but again be aware that under the heater covers there is mains voltage electricity. Unless you have suitable experience I would recommend turning off ALL the power to the house at the main consumer unit before trying. And that assumes you have only one consumer unit.
  3. Not Too Sure

    Not Too Sure Member

    Thank you for the response - having gone through some paperwork and a bit of fault finding, it looks like it is number 1 on your list (faulty valve) - the central heating one next to it failed last year so guess now it is the hot water valves turn!

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