Good points all, but....
It's not so simple.
First, adjusting the aquastat to a higher temperature changes the high
limit, which is not the always the same as raising the actual
temperature of the water. Most boilers, during all but the coldest
weather, will not get the water temperature up to the high limit
setting very often. Remember, the burner only fires when a zone is
calling for heat (and the water temp is below high limit setting).
Since most boilers are selected to have sufficient capacity to heat
the house even when temperature is at the design low, when the outside
temp is warmer, the house reaches the thermostat setting and shuts
down the burner before the water temp reaches high limit. The only
time my boiler hits high limit is first thing in the morning in very
cold weather when the system is raising the house temp from the night
setback to normal temperature.
It takes the same number of btu's delivered to the radiators to
maintain your house at temperature whether the water is at 140 or 190.
It's true that at a lower water temperature, the circ will have to run
longer to deliver those btu's, and several have pointed out correctly
that this costs real money. But running the water temperature higher
increases the standby losses up the stack, which also costs real
money. If you have an automatic vent damper, this helps this
somewhat. Standby losses are also increased when the standby time is
increased. Running higher water temp means more and longer standby
periods compared to lower water temp. Comparing the cost of
electricity to gas is irrelevant; you are not comparing electric heat
to gas heat. In this case, gas is always heating the water,
electricity is pushing it around. You save electricity by running the
circ less, but you pay it back by making up for the standby losses
with gas. Which factor wins depends on average temperature, boiler
efficiency, presence of vent damper, how well the boiler is matched to
the house, and on and on.
While running at lower water temp means the circ will run more, this
actually tends to deliver more even and comfortable heat, with fewer
cold drafts during the off time of the circulator. Yes it costs more
to run the circ longer, but some are willing to pay for more even
heat and the comfort. Again, this is offset also by the reduced
As I said, it's not so simple.