My RUUD 90PLUS won’t start after a power outage

If it was running when the power outage happened, that may have "fried" the control panel.
She needs to have it checked by an appliance repair person to see if that is so.
God bless your efforts.

Check the flame sensor is clean and connections are good . check pressure switch and hoses .

check the control fuse that protects transformer might be 3 amp fise in air=handler.

Check the ignitor circuit.

Send direct power to the blower by bypassing relay . See if motor runs

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there is a fuse on the circuit board on the inside unit. Typically a power surge will pop it. checking that fuse is the best place to start

Power surge may have taken out your control board (in the furnace, does the fan work?), possibly the transformer (in the furnace) or possibly the capacitor (in the A/C). Call a professional.

Your furnace is going into a lockout condition, cycling the power resets the circuit board and it starts over. I will need to know approximate age and model of your furnace, it sounds like you have need to clean the flame sensor rod. However i need to know what i am working with.

As for a filter if there was one installed it will be somewhere between the unit and the inside livingspace and are the black plastic supply vents wrapped with insallation or not ,if not they are the wrong ducts if you need more help just e-mail

What caused the power outage? Check the outdoor disconnect to the condenser unit. The fuses may have blown, causing the heat pump to not function and depending on the aux. heat to carry the load.