Problem with hot water 75 gal 1998 model Pilot fires, burner burns for 5 sec to 1 min then shuts off. What's wrong

Might be dirty burner,if capable remove and clean,, 12 years is a pretty long life for a hotwater heater

The burner just ran for 18 minutes?? The blower motor on top on the heater has been running all day?? Is there a danger is it keeps running all night, should I unplug it and turn off gas until I can get a professional to look at it or can I let it go all night ?

That blower is making draft for the exhaust, running does not real harm other than wasting power. Only unplug if you lso turn off the gas because the heater could come on later and not draft

That blower is making draft for the exhaust, running does not real harm other than wasting power. Only unplug if you lso turn off the gas because the heater could come on later and not draft

Thanks... I'll leave it on overnight then. What do you think is going on here ? No hot water all day but pilot/burner seems to be working. Why would blower run all day, isn't supposed to only run when burner is on ?

"No hot water all day " you mea no usage all day right? You will likely need a pro. There is an anticipator that starts the draft just before the igniton, it is failing to stop sending the signal to run the exhaust. Most cases this is electronic and not mechanical fix