He has contacted me to tell me "we need to arrange a time to come back and fit the CO alarm" only because Hetas had told him to.
He was asking me to see if I refused, which I didn't, nor did I agree.
He then told me that if I refused, he would have to give me a notice that the stove was 'unsafe'. Ha ha!
I told him that his refusal to respond to my messages regarding the install was his refusal to do anything about it, so I have contacted Hetas to see what we do now, given that he didn't get back to me within the 10 day period given to him by Hetas.
Small claims court is probably the only option.