We have been happy with TLC Plumbing. They are probably not the cheapest, BUT they have always shown up for us when they say (VERY important to me with young, napping kids) and have done good work for us. I'm not sure what kind of heating work they do, but they've helped us with our wall heaters, basic bathroom plumbing and we just had to have our entire house replumbed after a disasterous pipe leak and home flood. And once our water heaters prung a tiny leak and they came out and ended up not charging me to fix it.
With our flood, I've had to deal with contractors a lot and it stresses me out b/c they never show up when they say!!! BUT TLC was the exception.