Boilermate II - Thermostat part query

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Boilermate II - Thermostat part query

Post  Buckster on Thu May 28, 2015 1:55 pm

ever since I moved into our house a year ago - the BM II has constantly been demanding heat from boiler,green BMII LED on, boiler short cycling and always showing a demand requested

pump continuously running, and boiler short cycling

had gas engineer service boiler, change boiler thermostat, to no avail - he checked temp of boiler @ 76C max and thought that it might not be quite to as high a temps as it should (he was expecting more like 80) - and that might be why the BMII was always demanding heat - but looking at the thermostat on the BM II I wasn't convinced as it implied range was 65-80 depending on summer/winter

ok long story short, whole year its been on short cycling wasting electricity and gas, - gas engineer was going to do some research but never came back to us - I was worried to play around with it myself too much over winter as some heating (expensive) better than none if I messe something up

roll on to this week and I decided to take a plunge and change thermostat on BM II - had been suggested on here, and looking at circuit diagrams etc (I'm an electronic engineer by trade - but hands on experience very lacking) - the thermostat on BM II looked like by far most likely candidate if to me the only candidate for the symptoms

fitted the thermostat today - even without power on I could feel when turning the spindle, a positive click on/off - so a good sign, and sure enough after turning back on power to system

boiler fired for 10 minutes (I guessed BMII was full of hot water anyway)
green LED went off BM II
boiler turned off
boiler went to solid yellow LED (idle) - its never done that before - its always been flashing green as part of its demand/short cycling
BMII - boiler pump continued for about 4-5 mins (so delay PCB must be working)
BMII - boiler pump turned off

SILENCE at last !!!

so think may have fixed it - so thanks for previous help

nothing is always that simple though - and the part I was sent doesn't quite seem right

right part no.etc - looks almost physically identical - EXCEPT at bottom of spindle there is no "horse-shoe" wiper to only allow it to turn 180 degrees. The casting is on the metalwork at the bottom of the spindle to "stop" the spindle at each end of the range, but with no wiper on spindle itself to catch on the casting. Therefore you can turn the spindle about 4 full rotations, vs original part only 1/2 (or 180 degrees)

the horse-shoe wiper doesn't look like it could fall off even if man handled - so I can only guess either part has slightly changed or its a manufacturing defect (they missed a bit off)

any ideas/anyone else seen this please ?

thanks for any help

hoping for slightly lower gas/electricity bills now !

Buckster

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