Not really. It would be possible to go further if we at least had a schematic, but tracing a schematic from a board isn't easy and requires some experience. With a schematic you can compare voltages on a good board and a bad board and we should be able to figure out which difference is causing the microcontroller to refuse to enable the heater (assuming that's what's happening).
It might be helpful to know the markings under the sticky labels on those ICs, and measure the pin voltages on a good and bad board. But without a schematic it would be hard to diagnose the faulty component.
Have you measured all the semiconductors? Do you know how to check diodes and transistors?
I guess you've swapped both programmed devices over between the two boards and the fault stays with the faulty board?
What external components and devices connect to the board, apart from the heater and the pump? There is a temperature monitor of some kind, right? Anything else?
I can trace out the circuit, but I'm a long way away. You would have to send me two boards, and the external temperature sensor and anything else that's needed (apart from the heater and the pump), and pay me for return postage or courier. Do you know anyone nearby who can do it?