Pilot lights but burner will not fire

The pilot light may mount too far from the main burner. When call for heat, gas valve open to let gas flow but pilot mount too far so a delay to fire may take place. when Burner actually fires, a in -rush will blow out the pilot flame.

thermopile should show 600mv clean thermopile . clean pilot so its strong and blue . see how that goes, may need new thermopile .

If the pilot is lighting and the thermo couple is in the fire and turned red and the pilot still does not stary on change the thermo couple. They are available in any home improvment store.

Tankless?... call service technician

Tank? clean arrestor screen, replace gas valve thermostat
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html

http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent

Gene

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

For (fire) safety, there is usually a thermostat that will turn off the gas if pilot light goes out.

So when you try to light the pilot you will have keep press & hold the pilot gas supply for at least 10 sec until the thermostat is heated up. Then only when the pilot light stays on continually, can you turn on the burner.

Forget about changing to a High pressure regulator!

First, never light when the pot is empty, you can fill with water if you have no oil. Open the door, check the thermostat and make sure it is turned off.(The burners will light if thermostat is on) Behind the thermostat you will see the gas valve. Turn knob to off, then to pilot. There is a notch at the pilot position. Now look up in the middle behind the burners and you will see the pilot assembly. Push in on the knob on the gas valve while you hold a long lighter close to the pilot assembly. Once the pilot lights keep holding the pilot knob in for 20 seconds. Now let off the pilot knob. Pilot should stay burning. Now turn the gas valve from pilot to on. Now turn the thermostat to desired temp and the burners will fire off and start heating.

The burners and pilot need to be cleaned.
Turn off gas and power, remove the burners and pilot. Clean with a brass wire brush. (Steel wire can be used but very carefully) Remove all rust dirt etc. reinstall and it should fire right up.

it also sounds as though the pilot injector could be blocked so when the boiler comes on it extinguishes the pilot & then when the burner goes off boiler shuts down, or also the pilot rate maynot be set right, so when the main burner kicks in it robs the pilot of the gas it requires.
It could be that, or there is lack of ventilation for the boiler, so you get flame lift off when the boiler fires?

I left it off for a couple hours and it fired back up.

Pilot won't light - natural gas or propane. check for a spider web in the burner tube. check no dust in burner tube. check surface igniter is lit. if pilot lights check flame detector - may be a millivolt generator - it is a small capillary with a copper tip in flame path. no fire will keep the pilot valve closed. replace the generator.