Heating system won't go off automatically (with thermostat)

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Old 02-09-16, 08:32 PM
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Heating system won't go off automatically (with thermostat)

Hi! My natural gas, hot water heating system suddenly stopped responding to the thermostat. No matter how much I lowered the temperature setting, the heat remained on. Then, still at the thermostat, I clicked it from Heat On to Heat Off but the boiler still remained on. So I had to go down to the basement and turn off the boiler using the on-off switch on the boiler itself.

So I'm assuming there's a short-circuit in the thermostat and the thermostat needs to be replaced. But a friend of mine presented the possibility that the contact that is the interface between the thermostat's electrical system and the boiler's electrical system might be defective-- he suggested that the contact might have somehow gotten stuck in a position that closed the circuit of the boiler, causing the boiler to remain on (except for when the thermostat inside the hot water tank of the boiler turns the boiler off).

So my question is: Is what my friend is suggesting possible? If possible, what is the likelihood of that compared to a short circuit in the thermostat?
 
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Old 02-09-16, 08:44 PM
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We need a little more information.

Do you have multiple zones/thermostats ?
Does your boiler provide you with domestic hot water ?
What is the temperature on the boiler gauge..... it shouldn't be going much over 180.
 
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Old 02-09-16, 08:46 PM
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Pull the wire off of terminal W at the stat, if the boiler shuts down your stat is done
If it does not shut down you got bigger problems
 
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Old 02-09-16, 08:50 PM
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Hi PJ. Actually, I have a really simple, no-frills system: no zones, and my hot water is supplied through a separate hot-water heater. By boiler gauge, I guess you mean the thermometer that registers the temperature of the water in the tank? Yes, I think the thermostat inside the tank ensures that the temperature doesn't go above about 180 or 185 degrees.
 
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Old 02-09-16, 08:55 PM
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Hi, TOHeating! Actually, I know nothing about thermostat operation and it's too late now to start fiddling with the unit-- I'm going to need heat during the night (I'll turn it on manually.) I assume that your instructions to pull the wire off terminal W at the stat would break the circuit at the thermostat even if there's a short circuit elsewhere in the thermostat. Is that correct?
 
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Old 02-09-16, 09:16 PM
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You could just remove the thermostat from the base without disconnecting any wires.
 
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Old 02-09-16, 09:19 PM
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PJmax, what would removing it from the base do? And do you have enough information to tell me whether my friend's notion could realistically be the case: that the problem could conceivably be with the contact-- stuck in a position that closes the circuit to keep the boiler on-- and not with the thermostat?
 
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Old 02-09-16, 10:17 PM
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The thermostat controls a relay that in turn sends power to the burner and pump. It is possible that the relay contacts have become burned together although that is not as common as the contacts burning and not making connection.

Removing the stat from the base takes it out of the equation.
 
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Old 02-10-16, 06:06 AM
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I was going to suggest that, but not all stats have bases these days.
Thought it would be less confusing just going for the W terminal.
Does the same thing, unless the problem is in the baseplate
 
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