UK Landlord Forum / Life

Hi all....
I'm new here and was hoping for some advice. I have a tenant who has point blank refused to have a new (free) boiler installed at the house. Can anyone tell me where I go from here? Can I insist that they have it done or am I lumbered with paying for repairs to the old one?
The tenants I currently have in the property are by all accounts slightly mad and my partner would rather we just threw them out but me being slightly more sensible (and worried about having an empty property) has put my foot down.
I have been called out on numerous occasions for fantasy problems like a leaking bath which turned out to be a few light scratches which weren't leaking at all and faulty electrics which the tenant got her own quote to repair for £120. My electrician fixed this problem for £26 and informed me that it was his opinion that someone had been tampering with the wires! I had to pay a plumber a hefty call out fee because the tenant had left the tap open when filling the pressure in the boiler up. There have been numerous occasions where I have had to call someone out to the property, having arranged a time with the tenant and then there has been nobody in when said tradesman arrives.
I am by no means a dodgy landlord and I obviously want to improve the property by having a brand new energy efficient boiler fitted which I wouldn't be able to afford to do without the grant, but this grant depends on the tenant qualifying (which they do) so what do I do now???