Gusmer H-2000 proportioning unit keeps blowing "Phase control" block

[ExtraThiccBoi]

Hi,
at our company (polyurethane foam etc.) we use Gusmer H-2000 proportioning units. They are very reliable, but one of them has repeatedly gone bad. The unit has a simple system for heating up the hoses with foam components. The system includes thermocouple temp reading + PID controller and hose current setting. On the bad unit, the first time we lost the hose heating, the "143PHC" thing has gone bad. It's a really well-potted cluster of components, I smashed the bad one into pieces, but unfortunately, I destroyed it so hard I couldn't reverse engineer it. There was a pot, SMD resistor, capacitor, a diode (maybe zener) and some 3-prong silicon device which I think was a triac. I managed to dig up some new old stock ones for sale and replaced it, but the hose heating died again. The only solution to make the heating work again is to bypass the SSR, but then, the current setting still doesn't work and the machine keeps tripping a breaker (it now operates in this kinda f.ed up mode because we need it to operate amap). If SSR is not bypassed, the whole system is dead. I include schematic and manual, hose heating system troubleshooting is on page 24. I don't have access to the machine at the moment, but I had a look at a similar one. I can post photos if needed. Please tell me what components to check/replace etc. The original analog temperature controller has been replaced with CAL 3200 PID.
Pages in Parts identification brochure: 69-74
Manual - hose heating troubleshooting: 24