Fixing Worcester Bosch MT10 boiler mechanical controller "on" switch

[clive.r.long]

Hi,

After 18 months the WB MT10 mechanical controller "heater on" override does not "engage". I can push the rotary slider to the on position , and the boiler fires for the heating, but the rotary slider just "pops" back to the central timer position. Is this a known problem? Is there a simple fix? At the moment I'm just rotating the timer to an "on" period to get heating during the day. £50-odd for a new timer? What utter crap. I had a 25 year old Honeywell timer on my indirect system (removed because the cylinder leaked and I needed the space the cylinder occupied). Honeywell timer never failed and had "on override" so I could switch on heating during an "off" period - but the timer still switched at the next on/off point. What a retrograde, rubbish implementation is this WB MT10 timer.

Clive

[kl]

The mechanism to implement to override broke on mine - it's fairly fragile and there's a really thin bit of plastic that holds a tiny spring for it all to work. I repared min by taking it to bits, putting a tiny bit of araldite one the engaging mechanism to the microswitch (1mm) then creating the 'on' override electrically, I threw away the tiny mechanism for the mechanical switch and drilled a hole in it to mount a toggle switch to do the override. To force the boiler on you just make the red wire open circuit.