Guest not listening to heater instructions at the time of check in

[Sunte0]

Hi Airbnb community I’m a little concerned for a guest that checked in at my new listing. They stated they were coming in for a business trip and needed a place to live almost acting as if they were tenants and not guest. 
I then asked if she was moving any furniture into the house and she stated no. 
At the time of check-in they brought a u-haul truck for luggage. I was very concerned about this and I contacted support they stated since there is no furniture it is okay so I I let that go. Just seemed really shady to me that she starting moving luggage through the windows to avoid the ring cameras I have.

Moving forward back to check-in I explained to this guest how to use a radiator heating system. 
It works very well but is old we do have a brand new boiler in the house that works great. 
My request at check in to guest were to not set the heat any higher than 75 as it’ll suck the water dry from the boiler. Thus causing it to possibly blow up. The guest then stated to me she understood and can agree to those terms. 
The very next day she contacts me stating one of the rooms are cold and she has it set to 80. 
I told her on the chat how I told her at the very beginning of check in not to do that. 
I came to the house immediately announced first of course. The house was hotter than a oven the water level on the boiler was bare minimum almost breaking point. 
Immediately I tell her again to not set the heat any higher than 75. I called my plumber and he stated set the heat to 65 in order to conserve the water in the boiler upon further inspection. 
I come back later on to install a lock box on the thermostat and to check the water level. Again the heat was set to 85 this time now I called Airbnb support and mention if They can’t come to an agreement I want them gone without a refund for the rest of the remaining month. 
support calls her and she agrees to follow my wishes In order to stay. 
I come check out the water level again today and the master room to see if it’s getting hot as now they’re staying 65 was too cold. The house alone is like a oven at 65-70. 
The thermostat downstairs had a lockbox I installed to prevent this now I inspect upstairs and she used the second thermostat I forgot about to 90 degrees again. 
I called support and told them and they’re stating this is not a safety concern requesting I give them a partial refund. 
I don’t see how this is right for a host especially when I was patient and more than reasonable she made a promise to me even though it wasn’t a listed rule because I have never had this issue. 
Does anyone have some advice on avoiding the refund????

I can’t see how she’s in the clear here. If it wasn’t for them I could’ve had another guest book my house and not do these kind of things. 

[Mike-And-Jane0]

@Sunte0 Your house description needs to say what you will set the heating to. Once you ask for a guest to leave I am afraid they will be refunded for the part of the stay they didn't make.

[Sunte0]

@Mike-And-Jane0 Yes understood my listing did not have house rule on how a heating system works. As I do not list how a toilet works or how a stove works? Usually I give my guest instructions things like that at the time of check-in.
In person I explained to the guest on the first day of check in how to use the heating system safely and not to exceed 75 as it’s a radiator system very old but brand new boiler. 
Second day of reservation the guest reached out to me stating the heating was not working in one of the rooms. Upon inspection I noticed guest had the heat past it’s breaking point causing the water in the boiler system to be extremely low and possibly blow up. The house was already extremely hot almost as if a fire can start from the heat. 

I contacted support immediately on the next steps on what I should do. They’re aware this wasn’t a rule I had but due to the circumstances we had two options to give the guest. 

1. cancel their stay with refund 

2. continue their stay as long as they can come to a new agreement with both parties including Airbnb on the phone to safely operate the heating system or will be asked to leave without refund. 

The heat was working it was a safety concern for both me and the homeowner. 

They wanted to be sure the boiler system wasn’t an issue. My plumber explained to my homeowner that the system will stabilize if we lower the heat within the limits of its restrictions. Heat 55-75 is more than reasonable to use. 
In the meantime the homeowner was very concerned for the guest if they were to follow to use the heating system safely. 

Even know they agreed to both me the host and Airbnb support to follow these instructions if I can continue with allowing them to stay with their reservation I said yes if you can promise to operate the heating system safely she states yes. 
The very next day she did it again and almost started a house fire so I called Airbnb support and they said they will ask her to leave now. She was warned many times even though we know it wasn’t a house rule we came to a solution during her stay that she promised to follow. 
She lied and did what she wanted to know resulting in her reservation to end. 
now Airbnb is trying to say I have to cancel her stay and give her a refund since it was not in my house rules??? 
it wasn’t I’m already aware of that and Airbnb host support stated they’re aware witch is why I called them for my concerns and to be instructed on what I should do. 
followed every single instruction Airbnb support gave me and then customer support promised I wouldn’t be penalized under these special circumstances.  
The guest choose option 2. With both me and Airbnb. So why would I have to give a refund after that point? If that were the case wouldn’t I have went with option 1. If my guest was going to be honest with me. This only happened due to a heating issue that was in result to misused.