Shower water was no longer hot.
I narrowed it down to faulty cartridge, so I tried to remove the handle to see what kind of cartridge do I need. But the handle was stuck. I was afraid to pull too hard to not damage the pipes.
I couldn't use a standard puller as the handle wasn't an axial-mounted one, the mounting screw was on the side. The only other idea I had was to cut the handle, hoping not to damage the cartridge as I wasn't sure if/how fast I could find a replacement. Too risky.
I already knew of Mr Rooter - they helped me before when I got stuck.
So I requested an appointment online at https://ottawa-on.mr-rooter.ca.
Got a phone call back in just a few hours and got the appointment for the next day - a 2h window.
Got another call about ~30min before the scheduled window: Luca was heading my way and arrived ~45min later.
He followed the tablet app-guided procedure, confirmed my diagnostic, provided an estimate and proceeded to do the work.
His experience paid off: he knew exactly how to pry and pull, the handle eventually got unstuck and slowly, slowly came off.
The cartridge was also stuck. It broke off in pieces. The last piece also took some time to get unstuck and uncovered the culprit: the bottom of the plastic cartridge and the rubber seal showed signs of melting - most likely the original installer soldered the pipes with the cartridge installed.
Next hurdle - the cartridge was a Belanger one, not commonly found in the stores. Luca knew where to call, quickly located a replacement (FC9AC008C) and went to get it, all the way in the East end.
Installation was much easier. Hot water as expected. Luca also checked the boiler and the mixing valve - all OK.
Only a $20 fuel surcharge over the initial estimate. The cartridge was included. In all a tad over 2h since he arrived.
No way I could have done it in less than a day (not even considering the considerable amount of stress). Well worthy.