Do you have a 3 zone system, or are you controlling one zone with 3 thermostats?

I've never seen 3 Thermostats controlling a single furnace, but the first place I would look is at the thermostat that actually works. If it has a problem and is passing current when it is supposed to be open you may not have enough juice to pull in the relays when the other 2 close.

To check, pull the working thermostat out and then call heat from one of the others. I bet the heat comes on correctly.

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"...the street finds its own uses for things"

The thermostat in and of itself should not turn the boiler on. You should have either a single pump with three zone valves or three separate pumps.

All the boiler does is care that the temperature leaving it is 180F. It goes on and off based only on its internal temperature. It doesnt care about anything else. So just because you have a call for heat it doesnt mean the boiler will turn on.

That being said, what youre describing sounds more like either the zone valve or pump is not functioning.

The third option is that you have air in the system preventing the water from getting to the intended zone. Which means you either need to bleed the system or perhaps the automatic air separator might not be functioning properly.

My HVAC told me change batteries in thermostats each year and to make their fresh before I call

This just happened to us. 2 of 3 zones worked but one was cold. It was a bad zone valve. Took guy 10 minutes to diagnos and fix.

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Harry: "I expected the Rocky Mountains to be a little rockier than this."
Loyd: "I was thinking the same thing. That John Denver's full of shit, man."

Ok thanks. The two zones that don't work aren't used much. We only use it when its very cold. I noticed that one wasn't working last year but now the third one isn't working. I can't imagine the thermostat itself is bad (they don't use batteries) on two thermostats. So maybe I should check the valves. Is there a way to manually open these in the mean time.

I have a Taco Zone Valve module.

We have a 3 zone hot water, baseboard system also.

It most likely is a bad zone valve.

I have replaced a few over the years. It's really easy to do, you just have to keep the wiring straight.

To test, you need 2 people. Have one person set the thermostat to call for heat, the other person watches/listens to the zone valve.

You should hear the motor run, opening the valve, and you can see the manual lever move also. If it doesn't run, you know you have a bad motor/valve.

There is also a microswitch that gets tripped when the valve is fully open, this is what actually signals the boiler to turn on (if the water isn't already hot), and I think it turns on the recirculating pump.

In the meantime, you can use the manual lever to open the valve. It won't trip the microswitch, but it will heat the zone when the working zone comes on.

If this was the case wouldn't the boiler still kick on? The same thought crossed my mind but figured if the boiler works for the one zone and not the others it's probably something else

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"I think I've cracked the code. double letters are cheaters except for perfect squares (a, d, i, p and y). So Leddy isn't a cheater... "

Sounds to me like you have some crud [scientific term] in the zone valves that are sticking them up. Sometimes rapping on them will free 'em up, sometimes manually exercising them will, albeit temporarily in both cases.

I've never tried pulling one apart and cleaning them, but you might be able to do that and buy yourself some time.

Essentially, I'd say because they aren't used often they are getting corroded and sticking. Definitely get a tech in for a good cleaning and let him know what's going on. Hopefully you have a good reputable service company that won't gouge you. But the above might keep the heat flowing until they can get to you, and save you the cost of a service call.

- Jeff

Any update?