I think this is a Gaggia Baby specific question so I hope this is in the right section. My single shots are great but I am having problems with my doubles. I wait for my heater light to turn off and then I try to pull my shot. Half way through the shot the boiler light comes back on. I am not sure yet but I think that this is causing a drop in pressure and leads to worsening shots. I know the Gaggia has a small boiler but this shouldn't be happening. Does anybody have any ideas on what is causing this or what I could do to prevent it. I dont think that my tamp is too hard.

Boiler heater behavior sounds normal. As you draw cold water into the boiler during the shot triggers thermostat. Double shot longer than single hence more water being drawn into boiler. Heater boiler on or off has no bearing on the pump pressure.

The Gaggia needs a ~30 minute warm up regardless what the element light shows. Spend a bit of time observing the heat cycle as shown by the on and off of the light and try to start the pull just before the light cycles off. This ensures the element is on the entire duration of the shot.