Thinking about upgrading to the Eheim 2128 with Thermofilter. I was wondering if the heater module is replaceable and if it has it's own power cord that could be disconnected. My experience with heaters is that the thermostats go out and stick after a couple of years. Don't want to have to replace the whole canister if the heater goes haywire. Sure this is not the case but wanted to check with people that have experience with this filter. Also, how long have those of you that have the 2128 been using it trouble free?