Thermopile circuit?

[Teledog]

Hi all!

Recently had a gas hot water heater installed - NO electrical hookup to it, whatsoever.
The controller (Honeywell) has a status (pilot) LED that pulses every ~3 seconds or so.
Did a bit of research & don't believe there is any battery in it at all.
I've read that the Honeywell controller uses a "thermopile" to generate ~350mV for the indicator? Not sure of the accuracy.
{edit: from what I can gather, the HOT working voltage should be ~658mV, at minimum 350mV}

I'd LIKE to make the same sort of passive indicator on our ancient boiler  -for a pilot light indicator.
I've looked around & haven't found any schematics out there for building such an indicator circuit..
Is it a proprietary thing?
TIA! 

{2nd edit:  nevermind..discovered the LTC3108 ..groovy stuff}

[Vtile]

Peltier element can do it. Ie. search for "BioLite".