Heater only turns on when T-stat is lowered

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Aug 12, 2015
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Maybe someone here with more hvac experience then me can chime in.

Had a contractor come replace my ancient boiler this summer with a new one. He wanted an additional $2k to install a zone control unit. I passed on it and was using the original control set up(t-stat directly wired to zone valves).

I ended up installing a Taco 4 zone valve control unit. Everything is wired correctly according to the instructions. Boiler turns on, water heats up. I have heat everywhere in the house. My issue now is if the thermostat is set above whatever the ambient air is, there is no call for heat. If the thermostat is turned lower than the ambient temp, it calls for heat.

It is going the opposite of what the thermostat tells it to do. These are older 2-wire thermostats that have a silver fluid(mercury?) in it. I have swapped the R and W wires and it made no difference. I am lost as to where to look next.

I added a ground wire to the box and now T-stats won’t call for heat at all.
 
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I don't have an answer for your question, but I do know that the polarity of the wires at a two wire thermostat should make no difference. It's like a light switch -- the circuit is either open or closed.
 
I don't have an answer for your question, but I do know that the polarity of the wires at a two wire thermostat should make no difference. It's like a light switch -- the circuit is either open or closed.

I figured it wouldn’t do anything too. It’s just odd because if you want less heat, the heater turns on. If you want more heat, it stays off. Almost like it’s wired in to accommodate an air conditioner.

Now it wouldn’t be too bad of an issue since the heat does work, except as the heater heats the room up it’ll just keep hearing til I turn the t-stat up.

Could it just be bad thermostats?
 
Does this thermostat have a heat/cool switch? Maybe the switch is labeled backwards?

No heat/cool switch on any of the thermostats. The thermostats and boiler worked fine before the Taco zone control was installed. I get a feeling that it’s a faulty control board at this point.
 
That 4 zone relay might have a priority switch that if the priority zone is calling for heat or to an indirect tank the other zones will not run.

While things were down ya shoulda converted to 4 circulators. I dislike zone valves. Not too familiar with that relay cause its not needed unless ya need a priority circuit. Are those relays nc/no ? Maybe circulator on wrong side of relay contacts? End switch is triggering boiler....could be simple stuck rotor on circ...smack circ on cast housing and see if it runs...are the zone valves open?, no circ?
 
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That 4 zone relay might have a priority switch that if the priority zone is calling for heat or to an indirect tank the other zones will not run.

While things were down ya shoulda converted to 4 circulators. I dislike zone valves. Not too familiar with that relay cause its not needed unless ya need a priority circuit. Are those relays nc/no ? Maybe circulator on wrong side of relay contacts? End switch is triggering boiler....could be simple stuck rotor on circ...smack circ on cast housing and see if it runs...are the zone valves open?, no circ?

The boiler side of things work right. The issue is between the thermostat and control board. I have too much heat lol.
If I crank the t-stat up above the ambient room temp it shuts off. If I lower it below ambient it kicks on. The zone valves will open and close accordingly. I don’t have anytbing hooked to the priority zone at the moment. Priority is turned off.

I am using the low water shut off to turn on/off the unit. It was how the installer left the wiring on it. I can’t seem to trace any kind of backwards wiring that might indicate it’s wired as an air conditioner.

Worse case I can revert back to how it originally was and have the t-stat directly control the zone valves while the boiler is running all winter. But i put a few weekends into running the wiring for all of this so I rather have it work then not.
 
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Sounds like the zone valves are wired backwards, opening when they should be closing.

If you turn all the thermostats down to 50, does the boiler stop?
 
Sounds like the zone valves are wired backwards, opening when they should be closing.

If you turn all the thermostats down to 50, does the boiler stop?

Nope. Crank it to 50 it’ll keep running til I decide it’s too hot. Crank it to 80 and the boiler turns off. It’s basically an on/off switch at this moment, with the deciding factor being whatever the ambient temp is reading on the specific t stat.

Could it possibly be the zone valves wired backwards? The wiring looks correct from the diagrams on the zone valve. Will check again in abit. The bridge between the t stat and zone valve is the control board. If I remove the control board, everything works in harmony.
 
Brand and model of thermostat. Pic of wire terms at stat. Stat is either wire or program wrong set up.?
Taco model number and are using it for dhw priority.

All 3 thermostats are older Honeywell mechanical dial control with mercury in them. Can’t find the part number anywhere on the thermostat. They are 2 wire units.

Taco ZVC404 4 zone valve control. No DWH priority. I have the pump end switch wired up to the low water cut off. Nothing connected to the circulator.
 
Pump end switch....ya mean the feed to the circ? The Taco relay end switch should turn on the aqua stat on the boiler . That turns on the burner and circ. I'm in Schenectady so you are not that far away so controls should be whats around here. I'd put the low cutoff in series with the end switch from the Taco relay and the boiler aquastat..assuming low volt lwc. Some of the new relays might have a place to wire it to.

Sounds like yar gonna need to start over..

Do your thermos use a subbase for a/c and heat or only a heat sub? T87 probably thermos. There are several sub's for it.
 
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Wires on sub base R and W also look close at the heat anticipator ( wound wire with a adjustable slide 0 -.9 amp) if wiring is burned or the mercury is discolored ,dull or black. Bad stat.
 
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