What causes a tank to leak and then not leak

Here is the synopsis -

Yesterday - Slight Leak
Mopped Up

Today - Leaking like a sieve
I had to mop up every 10 minutes as we do not have a drain in the location

However, I turned off the pilot and also the inlet feed from 1 PM till 10:30 PM.
I had the pilot turned back on since 10 PM and as of not, it's not leaking at all...

I have a scheduled appt to have the boiler replace. Thoughts, suggestions, etc ? Should I keep this old 40 year dinosaur or replace it with the one that's coming it. Kenmore (AO Conservationist ) model ...... Will it be much more energy efficient ?

You didn't mention exactly where the water was coming from. If it is coming out of the relief valve, the cause could be too-high pressure in the house, and nothing at all wrong with the WH.

leak

Pilot on at 10:00, but did you also turn on the water feed? If the leak is a small one, then it could closed over if the pressure is off to give it a chance to "skin" over.

I could not pinpoint it but it was coming from underneath the unit.

I did notice that it would not leak if the cold water was off.

I turned the pilot on at 10PM and the water feed at 10:30.
Regardless, I'm thinking it's just crud that has skinned over and I should replace it.......it was leaking pretty bad before.

I'm not sure what is generally covered under a normal install but I assume the plumber always needs to end up reworking the pipes a little, to get the fittings to match the boiler.

I'm thinking I may just run out early tomorrow, pick up some ball valves and some fittings.......and finally replace/add stop valves. I've always had to turn the main since there is not a stop valve that stop water to the 1st floor and above......just recently had the kitchen done, and what a PITA turning on/off the main.

When your out, I think you should pick up a water heater too.....