When the boiler in my house cycles, the lights dim all over the house.

Is there anything I can do to limit voltage drops like this? My house
has 200amp service; the boiler is on a 20amp circuit with 10 ga
aluminum wire (this is the correct size wire for 20amp); and the cable
between the socket on the outside of the house and the 200amp panel is
enormous.

What can be done? 200amp service for the house is an incredible
overkill. My guess is that the house usually draws 40amp or so during
busy periods, fewer amps otherwise.

Thanks, Michael