Heat is circulating on one zone when there is no demand.


Old 12-02-17, 05:56 AM
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Heat is circulating on one zone when there is no demand.

Let me preface this by saying that I am not in the position to hire someone to investigate this and fix it. My money is very tight atm. In addition, this situation was briefly looked at when I had my new boiler installed and they couldn't figure it out at the time.

Zone 1 (basement)
Zone 2(main floor)
(Zone 3 (2nd floor)

I have 3 zones. Zone 1 and 2 both function. Heat is not circulating until there is a demand sent from the thermostat. Zone 3 has heat circulating when there is no demand from the boiler. It seems to be circulating in tandem with zone 2. Though as far as I know, Zone 3s zone valve is properly functioning. So the thermostat on zone 3 reads about 3-5 degrees higher than it is set for. And one bedroom where there are more baseboards than probably necessary is hot. So much as so we open the window or run the window AC. What could be causing this? This has been happening for about 4 years. I typically just live with it because it's only when we are sleeping that our bedroom is hot. I had a new boiler installed 3 years ago and this occurred prior to the new boiler. The install was necessary and not related to this issue. Please let me know if you have any thoughts.
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Old 12-02-17, 06:17 AM
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Note: Not an HVAC pro.

If zone 3 has its own thermostat, disconnect the wires and see if the zone stops circulating and/or the zone valve closes. Also, I would think if no zones are calling for heat the circulating pump should not run. If disconnecting the wires fixes the issue, replace the thermostat.
Old 12-02-17, 06:45 AM
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HI,does Z3 get hot when Z1 is calling? You could try disconnecting the wires from the Z3 Tstat and see if that solves the problem.

Old 12-02-17, 06:52 AM
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If the bedroom that gets hot is part of a zone, and you can't reduce the heat in that bedroom, remove the front cover and cover part of the fins with aluminum foil. You will have to experiment with how many lineal feet to cover. Add some , then if the room is still too hot add more to the lineal feet until you get the room temperature to your liking. You only have to cover the top of the fins.
Old 12-02-17, 07:06 AM
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If disconnecting zone 3 thermostat doesn't change anything, maybe you can swap the zone valve with another zone valve to see if the problem follows to the next zone. If it follows, the zone valve is bad.
Old 12-02-17, 08:59 AM
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Since it wasn't working before the new boiler and the person who did the install couldn't figure it out, you first need to determine if this problem has been there since the original installation or if a component has failed.

Do you know for certain that this system previously worked properly?

Some pictures would help.

Old 12-02-17, 09:50 AM
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You said 1 & 2 work only on a demand for heat but something is sending heat to 3.

First you must determine if it's mechanical or a piping problem.

Before disconnecting things I would try turning down all stats and then one by one turn them on and see what effects 3. Start with 1 and go down to basement and with #1 running see if the pipe gets hot right after the #3 ZV. If the pipe is cool it's not the ZV or the stat on #3 so you can eliminate mechanical.

While you have #1 running check your bedroom and see if it is getting heat. Even though your ZV is working they may have somehow piped some part of #3 into #1 circuit. If everything is normal then do the same procedure with zone 2. First check the pipe right after the #3 ZV and the bedroom. If the pipe at the ZV is cool but the bedroom is heating then you can start tracing your piping to find the problem.

When this problem occurs you can check to see if the whole zone is heating or just part of it and which direction the heat is coming from. It may be backfeeding somewhere. First check the pipe where the heat should come up and then follow the circuit to where it returns. It's just a little detective work.

Finally after you've done your investigating you can turn off #1 & 2 and try #3 by itself and see if any of the other zones are affected by that zone.

Zone 3 stat would read a little higher than set if you have unwanted heat in that zone. It doesn't mean the stat is bad, just more heat than what you want. If your stat reads higher than set then that zone probably never comes on I imagine.

One final thought. You never said if you get your hot water from your boiler also but with zone valves it shouldn't matter unless your ZV isn't closing all the way and then you could be getting some hot water in that zone by gravity which would happen when any zone called. That is something you can tell quickly by checking the pipe right after the ZV though.

Since the problem was there before the new boiler my guess would be in the piping somewhere.

Just my thoughts.

Hope this helps a little.
Old 12-15-18, 11:32 PM
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Unwanted heat in one of your zons.

Had the same problem and ending up draining the expansion tank. Apparently too much pressure building up and gravity feeding heat to that zone. Since my remaining 2 zones stayed cool, I suspect I may have a weak check valve which lets water pass too easily when pressure builds. Have a service contract, so if it happens again, will get the valve replaced. My system is old, and believe newer expansion tanks behave like this when they fail.
Old 12-16-18, 10:53 AM
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Glad to hear everything is working but at the risk of being the bearer of bad news here goes.

Expansion tanks, full or empty or in between will not effect or cause excessive pressure on the components of your system, except for the relief valve, which will relieve that pressure at 30 PSI to a safe level.

Your check valves and zone valves and any other fittings connected to your piping all have higher ratings than 30 PSI along with your baseboards or piping so the pressure would have no effect.

Next and last is the fact that check valves are not necessary with zone valves and you most likely do not have them, and if you do it would make no difference because the zone valves are positive shut offs and if the check valve was leaking by, the water could not get passed the zone valve.
Old 12-16-18, 01:11 PM
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Unwanted heat

What Spott said. Sounds to me like zone 3 zone valve us stuck in the open position. If there is a manual operating lever on the valve, first make sure it is not in the locked open position, next, with power off, try to move the lever, if you can move it without resistance that means the valve motor is stuck open but not necessarily hitting the end switch to turn the boiler on. I would start with that.
Old 12-17-18, 10:00 AM
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Whatever, all I know is when the service man drained the expansion tank, the problem went a way. Same situation with unsolicited heat occurred a few months later, so I drained the tank again, and problem went away. If it happens again will call my oil company to nail down the problem. Thanks for your feedback.
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