When the pilot light button is released the flame goes out. (pitco propane fryer) - unsure of model number as data plate is worn. Does the thermopile need replacing ?

If the pilot flame does not hold after releasing the button for at least 20 to 30 seconds, try to clean the thermopile and tighten all wiring connection on gas valve, thermostat and hi limit the repeat the process. The thermopile must be heated by pilot flame in order for it to generate small amount of voltage to open the pilot valve.
If this does not correct the problem, try replacing the thermopile.

Check and clean the thermopile, it is the cylindrical piece of metal standing behind the pilot assembly.Try also to tighten its wiring connections to the gas valve and high limit.If it does not correct the problem, replace the thermopile.

check if the thermopile (cylindrical metal standing behind pilot assembly) receives enough heat from pilot flame. if it does, you need to replace the thermopile.

Check if the the gas pressure is sufficient (as stated on unit's nameplate). Check if the hi limit device is good. Check also if the thermopile (cylindrical metal with two wires standing behind the pilot hood) is receiving enough heat from the pilot flame. The voltage generated by thermopile should be 500millivolts in order to open pilot and main valve. If there is 500millivolt on gas valve thermopile and the pilot flame does not stay lit, you have to replace the gas valve. If the thermopile is glowing red and the voltage generated does not reach 500 millivots, you have to replace the thermopile.

Check if your pilot flame sufficiently heats thermopile during operation and make sure also that it is free of soot or any form of dirt, thermopile generates small amount of electricity to energize pilot and main valve of the gas valve for pilot and main burner operation. This electricity passes through hi limit mechanical contacts. Hi limit on fryers act as safety device which will shut down pilot and burner flame when oil temperature reaches 450F.
If your fryer is set at 350F and over shoots up to 450F (which will trip hi limit and shut down pilot and burner flame), the thermostat is not good, but, if hi limit trips on temperature much lower than 450F, hi limit is bad.

Check if the flame quality of the pilot is good. Small amount of voltage generated by thermopile used in energizing pilot main valve coil during fryer operation relies on the quality of pilot flame, also, the thermopile itself should be free of soot or any form of dirt in order for it to absorb the heat from pilot flame.
Check also the gas pressure, it should meet the gas pressure required on the nameplate.

Better check the incoming gas pressure first, it should match the requirement as stated on the nameplate. Low gas pressure will make the pilot flame small until it could not heat up the thermopile which will shut both main burner and pilot flame.

Sounds to me the thermopile (thermocouple) is at fault, it's a safety device to detect if the pilot flame is alight or not. If the pilot should go out for any reason, the thermopile will detect this & shutdown the gas valve (ie the unit will cease to operate).
A new thermopile should solve your problem. It's not a task I would attempt yourself if you are in any doubt.

if you changed the thermopile and still have the same problem make sure that the sensing bulb is directly over the flame. If it is and the thermopile is installed correctly the next thing would be the gas valve.

Hope this helps

This device actually uses a thermopile it is part number P5047541. There are two things to check here ensure that you have had the right part installed be verifying the part number and also check that the sensing end of the thermopile is directly in the path of the flame.