This house sounds like a abomination of random circuits and unless it is really old, it sounds like someone withoiut a clue has been messing with the wiring. Kitchen receptacle circuits are not supposed to be shared with other (non-kitchen/dining/breakfast area/pantry) areas. Different branch circuits should not share "hots" and "grounds." The only exception is a multiwire branch circuit, but that doesn't sound like what you have here.

Given what you describe, it's hard to explain how to fix it given the scant information available to us, but I'd recommend getting someone with a clue to either diagnose and repair it or remove it all and start over.

I agree with ron. It sounds like a mess and it's hard to tell what's going on from your descriptions.

It looks like the 240V circuit that feeds the baseboard heat has it's neutral and one hot mixed into a 120V circuit.
Do you know where the cable for the 120v circuit goes from the baseboard heater? It seems like you are assuming it's the bathroom light and vent hood, but if that was the case, then they would (probably?) still work when their breaker is off but the baseboard heaters are on.

...then there's a termination into the thermostat and the 120V continues on to some kitchen outlets
Again, are you sure that's where the 120v cable is going? How do you know?

The 240V heat circuit would not normally have a neutral. Is it a 3-wire cable (Black, red, white)?

I'm confused-- where/how do you get a 240v wire in house wiring? Each of the two hot wires in a 240v circuit should be at 120 relative to ground/neutral, no? Is this a 480v 3-phase service delivering 277v on one branch?

I'll open up the junction box again this weekend and verify. I'm going from memory on the bathroom circuit, but I distinctly remember a black-red-white-ground. I'll check the main electrical panel too, since that will tell me for sure. I'd post the pictures I took at the time, but I'd need to label them, and that might take me some time.

First you said the 240 circuit has a hot and a neutral mixed into another circuit, yet when you turned off the 2 pole breaker the 120 loads still work? This makes no sense. This could be a legitimate setup that you do not understand or it could be hack, very hard for us to tell over the internet and even harder for a novice to try and figure out. The others are correct that a 240 circuit does not need a neutral, also how did you determine it was a neutral? Just because it is white does not necessarily mean it is neutral. Maybe it is part of the thermostat wiring, or maybe it is a neutral and continues on to another heater that is 120 volts. I am going to suggest that you get an electrician in there to help you out just so nothing bad happens.

This post was edited by joefixit2 on Fri, Sep 5, 14 at 10:00

I think you are right. Too many unknowns for my lack of experience. I'll post back once I have an electrician describe it to me.