Have a forced hot water system for home heating that uses the typical 2 wire Honeywell thermostat to control a Honeywell RA832A switching relay.
The switching relay closes the circuit to the thermopile, as well as closing the 110 V circuit for the water circulator.
There is also a transformer that provides 24 V for the thermostat and the relay.
Guess I'm dating myself somewhat here, but there is a symbol that I am not familiar with in the instruction sheet for it.
The secondary of the transformer (going to the thermostat) shows what is similar tho the common resistor symbol of3 points up, and 3 points down from the baseline.
But this symbol has only 1 point up, 1 point down, and then the return to the baseline.
I don't think it is meant to be a resistor.
It is drawn close to the relay contact symbols.
Could it be meant to be the coil for the relay, perhaps ?