Setup: Intermatic Digital Timer (P1353ME) + Pentair VF Pump + Minimax NT Heater

Short story: Turning the heater on/off via fireman's switch is not working.

Details: The pump is programmed with its own timer to go on and off at programmed times. The Intermatic timer is "synchronized" with the pump, such that the heater will be switched off 20 mins before the pump shuts down. So I am using one of the timer's 3 circuits for this purpose.

Problem is that at the end of the cycle, when everything shuts down, the heater displays "Err" and will not turn on with the next cycle. However, if I turn the heater on and off with the switch on the inside, it will work fine until it has to start again at the next cycle.

The wires from the timer connect to the circuit with the thermal fuse/ low pressure gas switch (yellow wires). This is how it was setup to turn the heater off from an external switch.

Any ideas how to remedy this? Do I need a new DDTC board? Was this wired properly?