wrote in message
...
Boiler does start as per times set (Twice: once in morning and once in
evening, two hours each time). Water tank gives hot water. But all
radiators in the house are cold.

This began after holes were drilled right above Thermostat that
dropped lots of fine dust on Thermostat and surely quite some got in.

Previously when turned Thermostat was giving 'kt' sound when room
temperature was crossed. No such sound any more.

Your boiler is up to proper temperature (that's why you are getting hot
water). It COULD be your thermostat, but it
sound like your circulator is not coming on. That could mean several things.
Could be a broken coupler (if it's an older
system), could be a bad aquastat/relay, could be a bad motor on the
circulator.

You could gently blow the dust out of the t'stat with some compressed air,
or do it yourself like you are blowing outa candle. DON'T pour anything into
the thermostat! The service guy will be replacing a lot more stuff if you
do.