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Mira Event XS Thermostatic - No Flow

Discussion in 'Plumbing and Central Heating' started by AWD99, 28 Jul 2017.

  1. AWD99

    AWD99

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    I have a Mira Event XS Thermostatic that's been (professionally) installed and working perfectly for at least the last 10 years. I'm the only occupant / user, so usage is relatively light. Recently the motor has sounded just slightly different, and the pressure has been possibly slightly lower, but I really do mean 'slightly' - until this morning, it was running OK this morning for maybe 3-4 minutes, stopped when I turned it off, and then wouldn't start again - in the sense of the on/off button still works, the motor sounds to be running, but no water... only a dribble / drops.

    I've just turned the electric & hot / cold water feeds off, and cleaned the inlet filters. A small amount of water (1-2 litres) drained out of the cold water side, but very little from the hot water side (100ml maybe) - both are fed down from the ceiling space. The filters weren't really dirty, and the 'O' ring seals were still good - all cleaned and refitted anyway.

    While the inlet filters were out, I cracked each of the isolation valves open, enough to get ltrs/min flow from both sides - they look about equal flow, nice clean water.

    Also, while I had the filters out, I checked the resistance across the solenoid coil = 3.7k Ohms (with the wiring still attached, but all electric off).

    Restored the water supplies and electric, and tried the shower again - no change. I tried lowering the shower head to ca. 1m below the unit, putting the pump on full speed, and temperature on full cold, and then full hot - no change, still no water after 10 - 20 seconds (didn't like to run it longer with no water).

    The motor is spinning, as is the small fan below it, and it varies in speed as the flow control is varied.

    Neither the outlet hose (new generic 1/2"), nor the shower head (original), is blocked - I can blow easily through both.

    I'm confused at this point:

    Is it possible the solenoid is mechanically 'stuck' shut but still measures OK on the coil ? (does that even happen ?).

    Thermostat fault ?

    Would appreciate any hints or tips anyone might have for further troubleshooting ?
    Thanks,
    Alan
     
  2. seco services

    seco services

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    More likely the solenoid is failing. they can be intermittent before they finally give up.
    You've done all the right checks.
     
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  4. AWD99

    AWD99

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    OK, thanks your help seco services - I'll get one ordered, and update as soon as I've fitted it.
    Alan
     
  5. AWD99

    AWD99

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    Stripped the old solenoid valve while I was waiting for the new one - the coil & plunger basically still looked 'sound', the internal black rubber 'diaphragm' appeared to have perished slightly at the edges, and may have been leaking internally. I cleaned it all up, and refitted it = no difference, some water for the first 10 or 20 seconds, then nothing, not even enough to half fill the damping vessel.

    The new solenoid assembly arrived this afternoon - fitted in 10 minutes - all back to normal. Full water flow, hot and cold, so I guess the damage to the internal diaphragm was the issue. The old coil still tests fine, so I can't see any other reason.

    Now all I need to do is stop the very slow drip from the filter cap..... that's a lousy design, one central screw to secure the 2 inlet filters. I suspect the slightest over tightening or distortion of the 'cap', and it leaks. Any 'tricks' ? or is it just a case of new O-rings (I forgot to order !) ?

    While I was in there, I did notice that one of the motor brushes was giving lots of (very very small) blue 'sparks', where the brush meets the commutator - I couldn't see the back of the other brush, but I assume it's the same. Is that normal ? or should I be getting a new set of brushes as well ?

    Anyway - a successful result, so many thanks again 'seco services' !
    Alan
     
  6. DIYnot Local

    DIYnot Local

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