Two zones; one triggers furnace, the other doesn't

1 Nov 2011
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New York
United Kingdom
We have a two-zone forced water system with a gas furnace. Both thermostats operate their respective valves, but only one actually triggers the furnace. So if the top floor thermostat triggers the furnace, hot water will flow to the lower floor system if its thermostat signals the need, but if the top floor thermostat doesn't turn the system on, the lower floor won't get any heat.

I've changed the thermostat and the Synchron motor valve. This hasn't helped.
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Post pictures of your valves, and by the way this is a UK forum, but we'll try to help anyway.
Electrical checks with a multimeter will be required to establish if your problem is with the head or valve body. Even if the synchron motor works it must also make switch to enable power to pass to the burner.
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hi, whilst the covers are off the actuators as in the photo check that the levers inside the actuators are opening far enough as to touch the microswitch when there is a demand for hot water.
Well, when I trigger the microswitch by hand the furnace goes on, so the switch itself is fine. I guess it's not being triggered...can I mount it differently so that it will be more easily triggered?
the arm needs to make the microswitch when theres a demand for heat or hot water, if it is not quite opening far enough for the arm to operate the microswitch its because the inside of the valve body has seized slightly, it doesnt look like your valves have removable heads so you can either bends the arm slightly or you can try and free the body by manualy opening the valve with a bit of pressure on the lever then let it spring back to the closed position, do that about 10 to 20 times and it should work. ;)

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