Sounds like you are doing everything right. I remember that the instructions also said, that if the humidity is too high, you can put a piece of tape over a little bit of the trough to get it down. So, you might try that, but it sounds like with the heater working, you will be ok. I hope you aren't somewhere where is really cold. A broken heater this time of year is NOT a good thing
I won't even tell you that the AC/heater unit has been broken since June. And our rental company hasn't come to fix it. The only thing that has saved us is that our house is new and REALLY well insulated apparently. It has been cold, even for CA, but it hasn't been too bad in the house. I guess I didn't notice the humidity going up. But all is well now, and this morning we are holding at 45 on the button!!