After calling a Professional, You don't want to ask Youself: "Could I have fixed that?"
There's very few things that feel as bad as calling in a professional having them flip and switch and charge you. You're both out money and can feel embarrassed, or in a professional situation and have a difficult time justifying this cost to whomever you report to. Usually this can be prevented in a few easy steps.
#1 Check Your Breakers: Breakers can trip for a variety of reason some of which may be a one time instance and not a point of concern. Before calling a professional I would recommend locating and resetting any tripped breakers, bearing in mind that there will typically be an inside panel as well as one outside by the meter. If the breaker immediately or consistently trips you still may want to take one more step before contacting a professional. In the effected area unplug everything and turn all switches off then reset breaker. If they hold, try plugging in items one at a time, then flip switches back on one at a time. If the problem persists or the breaker trips with something you cannot just unplug, it's time to call a pro.
#2 GFCI's: A GFI's primary function is to simply check for any voltage imbalance so it is pretty normal for these to trip intermittently. Unless they are tripping more frequently than once a week it is usually not a necessity to repair. GFCI's will be installed for all bathroom, kitchen, garage, and outdoor outlets will be on a GFI. Keep in mind that one outlet can run up to 10 protected outlets. so if you have an outlet not working in one of these locations, check and reset all GFI's in the house before calling an electrician.
#1 Frozen AC system: An AC will freeze for three reasons: low temperature, low indoor air flow, or low refrigerant. If you have a frozen AC make sure of two things before calling someone; Make sure there the filter in the unit isn't dirty, and make sure the thermostat is not set below 72°F. If you suspect either a dirty filter or low set-point were the cause set the system to off and fan to on for 3 hours then restart the system and it may resume normal operation.
#2 Backed up drain. Your AC will condensate up to 2 gallons of water an hour. This will run from the indoor unit and drain outside usually via a 3/4" PVC pipe. If sediment plugs up this pipe it will either back up into the house causing a mess or newer AC units will have an overflow shut off or "float" switch. If you have a blank thermostat or a system doing nothing you should first check this "float" switch for water. If this is full, empty it. Hook a shop vac to the outlet outside, pull the sediment out, refill the drain trap and reinstall the float switch and test the system.
#3 Tripped breaker, See above for testing a tripped breaker.
#4 Thermostat batteries, if the thermostat is blank make sure the batteries are not dead.
#1: Pilot light is out: On gas water heaters if there has ever been a interruption in gas service to the property, (even briefly) the pilot will need to be relit. Follow the instructions on the heater to do this.
#2: Tripped breaker: While typically a tripped breaker is a sign that one of the electric elements is shorted, it is not a bad idea to try resetting it and see if the problem still occurs.
#3: Tripped high limit: All electric water heaters will have a high temperature cutout safety on the upper thermostat. Should this trip repeatedly than there is a problem (if however you only have to occasionally reset it, it may not be worth repairing). This safety reset is a red circular button behind the upper access panel on the side of the heater.
#1: Make sure the pool pump is running and that it does not have a very dirty filter.
#2: Make sure all water is flowing through the heater and that there aren't any valves diverting water away from the heater.
#3: Check to make sure all breakers are on.
#4: If there is cold air blowing out of the top of a heat-pump heater, it is operating correctly and may just not be at optimal temperature yet. This doesn't necessarily mean its running at full capacity but would mean it is at least somewhat heating.
#5: Make sure the gas valve is on.