them boilers can develop a fault like that but since its like that from installation i would check wiring.
boiler:
live
neutral
earth
t1 ------ power from boiler to timeswitch
t2 ------ power back from timeswitch or room stat if fitted
timeswitch:
live
neutral (bits that keep everything remembered etc)
common (1) connection from t1 on boiler
con (2) ch off (not used)
con (3) switched live out to t2 on boiler
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if room stat is fitted it will lie between con (3) on timeswitch and t2 on boiler.
so con (3) from timeswitch would connect to common on room stat and calling from room stat would wire back to t2 on boiler
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iain
October 2008