I am putting together a project to replace our heater thermostat with a Tocuhscreen Pi solution, a touchscreen that plugs onto the first 13 pins on each row of the header.
This covers all of the 5v & 3.3v pins leaving me with an issue, because the relay and the temperature sensor both require power.
Is there a way to address this just using the 40 Pin header, or do I have to either select a different display method or different source of power for my components
You could consider breaking out a USB port (It’s the same 5V at least):
Otherwise, you could use a breakout like this one:
The way I read this is the temperature sensor and relay are powered at present which means you are looking at powering the RPi and display.
By thermostat do you mean the knob that sets the required temperature. In fact the temperature sensor and knob are all part of the thermostat so what are you actually trying to replace. Sometimes this knob and temperature sensor are an integrated pair and are mechanical which would make your task a bit difficult. Just about a redesign.
What sort of heater?? If gas be very careful as there is also a flame detector which shuts the gas down if failure to ignite. Also Oxygen Depletion sensor if you are running the heater in a confined space. Some time ago an acquaintance of mine just down the street almost blew the front out of his house by playing with a gas heater which he knew very little about. He was lucky to get away with a few minor burns.