When I first read this comment I was picturing a hot water radiator behind you, so it sounded unlikely based on the blackbody radiation curve for ~320 K.

But now I realize you're probably talking about an electric heater. Given that their heating elements get so hot that they're putting out visible red/orange light, it seems very plausible that an electric heater could produce enough ~940 nm IR to drown out the signal from the remote.

Thanks for sharing! I will try to keep this in mind when I'm troubleshooting IR remotes in the future.