Hi, Kinson. First of all, “air conditioning” refers to the device that cools down the room in the summer. You mean “(central) heating”, the device to warm the room up in the winter. Second, you seem to have made a mistake with the temperature, since 9 Fahrenheit is more than 10 below zero Celsius. If it were that cold in the room, nothing you could say would make the guest happy. Thirdly, the device that is supposed to regulate the temperature is called the “thermostat” (a word of Greek / Latin origin). Finally, if it’s colder than 70 Fahrenheit, you’ll need to get the hotel engineer to fix it, move the guest to another room, or provide a space-heater (portable electrical heater).

If I were in your place and this happened, there may be no way to make the guest feel happy. How cold is it in the room with the heater in its current state? If the heater really isn't working as it should and it is very cold inside the room, then the hotel should offer another room where the heater does work. If there is no such room, then maybe the hotel can offer a space heater. If you can't do that, offer a lot of blankets. There will be very little happiness if you can't make your guest warm. If you can't, then apologize profusely. For example, "I'm very sorry sir, but the room's heater is not working properly even though I overrode it to give the maximum amount of heat available. I am looking into getting you a space heater to see if that might help. I will send additional blankets to your room as well." ... Also maybe offer them complimentary drinks from the bar, or other free stuff, especially anything that will make them warmer. Good luck! Sounds like you're in a tough position.

Hello! You may try this. At this time, the sensor for our air conditioning system is not working correctly. Unfortunately, this may cause your room to feel very cold. We are trying to fix the problem and apologize for any inconvenience.