I regard the use of 85'C electrolytics on a board inside a boiler casing as a definite case of built in obsolescence. They're usually the first thing to fail (rapid cycling of the ignition sequence, trips etc.). That's assuming that things like the relay pins were flow soldered correctly in the first place.
You'd think so, wouldn't you?
I had cause to tape a thermocouple to one of the pipes inside my boiler a while back. After I'd got the readings I needed I couldn't be bothered to disassemble and reassemble the boiler to recover the thermocouple, so for a few months there was a type K thermocouple plug hanging out of my boiler.
Eventually I did need the thermocouple back and before removing it from the boiler I tried taking readings again. Low, way too low. On the pipe it was reading 50-60C, it was about 30C. So off comes the case and the tape that was holding the thermocouple had let go, leaving the thermocouple tip hanging in the breeze between the hot water outlet and the control board.
So the control board was sitting at about 30C ambient, no hotter, and in many cases cooler than inside bits of electronics that don't have a 30 kW boiler 15 centimetres away inside the case.
Moral of the story: the apparently reasonable assumption that inside the case of a boiler is really hot is, in fact, not necessarily true.