Chris Brooks.

Hang on Chris !!
All that crabs about controls are friendly talks keep a guy from the blue sometimes. I too, love the shop talk that’s why I’m here. But aren’t we a bit too control oriented? Phase angle and solid state relays are real and are for motor control mostly, where immediate reaction(we sometimes said tight control) is mandatory,but heating elements has to generate X calor over Y period of time to raise A weight of water to Z degree. In another word grab your cold,unused iron in your hand now plug in the mains, if within 30 sec you get burn then your iron is more superior than mine.Now back to reality, you said you have two pairs of wires for controlling your boiler what kind of signal they require 220 vac,40mA of current,or 0v-5v lo/hi logic to operate your boiler? Whatever they need we’ll give them but for now we are going to determine when to give them the sig.
For our black box it has to read two temp sensors one’s immersion type for the hot water,the other’s ambience type based on if pump run read ambience if pump stop read immersed.condition: operation enabled.
For the SMDs just salvage the sockets from old discarded CD Rom drives .
Happy programming