Hi, I had a similar problem when I lived in Canton Aargau. I was living in an old building and the first winter, I froze because the heating didnt work properly. So I paid the rent to a third party and it took three months for the problem to be sorted out. I would advice joining the mieterverband www.mieterverband.ch they were extremely helpful. Best of luck.
PS. another point, because the heating didnt work, I bought myself a radiator (which costs around chf 100) and had that on all the time. The mieterverband made the housing agency pay for the heating charges (as it was quite expensive around CHF 100 per month)