Furnace is high flow.
Gas for water heater is high flow.
If both do not work, it could be the opd valve in the tank has tripped. To reset, close tank valve, light stove for 10-20 seconds or until flame out and turn off.
SLOWLY open valve 1/4 turn, let gas slowly fill lines. When no more hissing, open valve the rest of the way. Light off the furnace. May take a couple cycles of the switch.
If the above does not work, you may have a bad control board.
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