As Bob said..... a regulator is a good idea if you were not using one because pressure can fluctuate and the unit is sensitive to water pressure.
That being said...... I assume you are getting no error messages on the control pad. Is the little flame icon coming on the display when you are running the hot water?
I would also turn the hot water on and got outside and check that...
1) The blower motor is running
2) You feel warm air coming out the exhaust port
That will at least confirm the unit is firing up and trying to heat the water.
What about your propane? Any changes there? Did you fill up recently? Have you made sure the valve is wide open?
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