I just purchased this house six months ago and it has a baseboard water heating system that is gas-fired. One zone is always on. I can shut it off manually on the return side. I understand that this is most likely a zone valve failure. I had an HVAC guy who was recommended to me look into this as soon as I moved in. He said he'd never seen these valves before and he'd find a replacement. Well, I waited all summer and we talked on the phone several times and, long story short, even when he showed up in September he had forgotten all about looking into it.

This is the valve:

Honeywell MZV series motorized zone actuator. I don't see a model number anywhere, but there are some patent numbers.

Then he said it was just twisted on wrong and the valve should work fine. Of course, a day or two later I realize it's not. It's always on.

The valve says something about twisting the knurled bronze part until the pointer is over the red dot. Most of my valves are not over the red dot. How much can I twist this without them coming off?

I had him repair a leaky baseboard pipe, which required that the system be drained. Then he took forever reflushing the system.

Well, now the main level zone is not even heating up. The upper level zones do heat up. Is this an air pocket? If I follow the pipes from the heater, they're warm until they come to a 90 degree downward bend, then they're room temp from there.

Is a system flush something I can do myself? I asked him about this when he was here, but of course he said he'd rather I call him (and pay him $98 an hour) to do it.

I'm willing to 1. replace the valve and 2. flush the system if you think it's something a mildly handy person could do. What do you think?

Chris