On Oct 18, 5:01*pm, Mike Clarke wrote:
Angela wrote:
I have a Honeywell CM67 on my central heating and I have noticed that it
is calling for heat several times an hour even though it states that it is
at the correct temperature. *When it is at the correct temp it only calls
for heat for a minute or two.

Yes, that's normal.

This seems a real waste.

Not really. When you heat your house up to your desired temperature it
looses heat to the outside world. With a "conventional" thermostat there is
some hysteresis which causes it to switch off until the temperature drops
sufficiently for it to cut in again, resulting in an erratic temperature.
The programmer uses some clever logic to provide enough heat to balance the
heat losses to the outside and maintain a much more steady temperature. It
does this by varying the length of time to fire the boiler every ten
minutes. When it's not very cold outside and you've arrived at the target
temperature the heating periods are quite short but get longer as the
weather gets colder.

Our CM927 behaves in a similar way and keeps the temperature at a steady
value within half a degree of the target.

--
Mike Clarke

Cycling 6x an hour, 144x a day is a waste in efficency and equipment
life, If this is a radiator HW set up its unbelievable, I cycle at 50f
outside maybe 8x a day. Your wear and tear on equipment is startup,
just look at surge load for motors.