Have a Triton Millivolt pool heater pilot is lit and nothing!!

so it is a millivolt .and the answer is yes there is a water pressure switch inside the heater, but also there is a internal flow control valve in right side of the heater,check by removing the 2 bolts, and look inside if there sand left ,by brucken laterals inside filter, also check for gas pressure ,the pilot stay lit ?

millivolt heaters generate their own power from the flame on the pilot max is usualy 750 millivolt, check all connections clean and secure.
Mmake sure the pilot is lit

Unfortunatly you probably have a bad gas valve.

possibly poor pilot adjustment or insuficient mv output from thermopile

make sure filter is clean, make sure filter is at 10-18 psi , also post if electronic or millivolt heater

make sure the flame hits the thermo couple if so then replace it lows has them in the water heater section thermo couple gets hot makes millivolt signal then opens gas valve