I'm a just signed up newbie making my first post. I'm a Canuck wintering in Gulf Shores Alabama for our fourth time. Our house sitter back home is having a problem with the heating. We have a 10 year old, oil fired boiler hot water system with five zones and using slant fin rads and all on one floor. The 4 zones for the three bedrooms and bathroom each service one small slant fin rad each and seem to be working fine. The biggest zone services 5 rads, consisting of 4 fairly big slant fin rads which is for the living/dining room, kitchen and 1 small rad at the bottom of the stairs going to the front door. That zone when operating normally has gone up to 74 F in the winter when it was accidently set too high and quite possibly could have gone higher. For whatever reason that zone seems to be acting erratically this year, sometimes getting that zone up to only 19 Celsius (66.2 F) maximum and sometimes only up to 15C (59 F). I had the thermostat changed but that had no effect. The boiler also heats an in-door swimming pool with it's own thermostat and I turned the heat down for while we're away and it's maintaining a constant 60 F, so it's fine. Is it possible for zone valves to for whatever reason start to act erratically? I hope that's the case because replacing the zone valve would be a simple solution. I hope someone out there in cyberspace might have some good input on my problem. Thanx for your attention and consideration.

I have a 3-zone system, with 3 Honeywell Zone Valves V8043F wired in series and 3 thermostats. The problem is only 1 thermostat is causing the boiler to fire. The other 2 thermostats correctly open the valve, but do not fire the boiler. I measured the voltage on the 3 valves with the thermostat off and on. When the good valve activates, the voltage is 24v on the thermostat wire and 0v on the endswitch (all 3 valves go 0v on the endswitch from this). The boiler is firing at this point. When the bad valve activates, the voltage is 24v on the thermostat wire and 24v on the endswitch. The boiler does not fire. The same goes for the second valve. The bad valves do correctly open the valve. I hear the click. I even watched the microswitch get pressed down by the motor. Yet the voltage on the endswitch stays at 24v. Does this mean the two valves are broken and should be replaced? [table="width: 200"] [tr] [td] [/td] [td]Bad[/td] [td]Good[/td] [/tr] [tr] [td]Off[/td] [td]0v/24v[/td] [td]0v/24v[/td] [/tr] [tr] [td]On[/td] [td]24v/24v[/td] [td]24v/0v[/td] [/tr] [/table] (thermostat wire/endswitch)