UK Landlord Forum / Life

Is this legal if it's in a property you are letting out? I understand they are a slight fire risk but I read about others doing it, and apparently it's used often as insulation material. It makes a huge difference to the warmth of the rooms above.

The boiler is in the garage. Modern, turns itself off in case of malfunction so I'm not seeing that as a problem...

Feel free to enlighten me. Thanks