Welcome! Here are the website rules, as well as some tips for using this forum.
test out like regular voltage. When using the lower DC scales on the meter to test the system and measure millivolt drop if a switch is open you may read the voltage drop back through the valve coil. If you are interested I have an entire procedure on testing self generating which I will send you via postal mail. Just e-mail me your address.
What make of pool heater?