Zone Activating When Not Calling for Heat

DrVetur

Hope I chose the correct category. I have 4 zone space heating with radiators and baseboard regulated by Honeywell thermostats (3 analog, 1 digital) and Taco 3-wire zone valves. I have noticed that Zone 3 will activate along with Zone 4 when only Zone 4 is the one calling for heat. Bad wiring? Of note, Zone 4 also seems to not be calling for heat until the room temperature is 2-4 degrees below what the thermostat is actually set at.

Jamie Hall

When you call for heat on zone 4 and only zone 4 -- by turning its thermostat way up with all the others way down -- does it turn on? Does anything else turn on? If only it turns on, but it does, then that thermostat may have a problem. However, if some other zone also turns on -- you mention zone 3 -- then there is a wiring problem most likely. What happens when you turn on zone 3 and only zone 3? From the sound of it, you may have two different problems playing with each other, which always makes troubleshooting fun.

DrVetur

After your suggested trouble shooting seems like zone 3's thermostat has the opposite problem as 4's: calling for heat too early. How costly/possible is converting Honeywell analog themostat's to at least digital if not "smart" thermostats?

Jamie Hall

Which model Honeywell analog? If they are the mercury switch type, the cost is zero -- adjust the level so that they are correctly levelled. Even a tiny amount off can throw them off several degrees.

If they are mechanical, it's either easy or vaguely difficult -- the critical factor being do you have a common wire going to the thermostat. If there is no common wire, there are many battery powered thermostats available -- some programmable -- which are very good and inexpensive. Try Home Depot or Amazon. If there is a common wire, likewise, of course. However, if you want a "smart" thermostat, particularly one which has networking capabilities, and no common wire, things get messy. Some of them claim to be able to work with two wires; they don't, at least not reliably. They really need an always on 24 volt power supply, which requires either an outboard transformer or a common wire.

DrVetur

Thanks @Jamie Hall. Leveled the mercury ones. No common wires unfortunately

Jamie Hall

DrVetur said:

Thanks @Jamie Hall. Leveled the mercury ones. No common wires unfortunately

You may find that they may actually need to be very slightly off level to have the "on" temperature exactly equal the thermometer dial. Depends on just how fussy you are!

EdTheHeaterMan

Regarding smart thermostats... Taco Zone valves may require an isolation relay in order to be operated by some smart thermostats.

The zone valves you have, work on a heating element that causes a wax-filled piston to expand to cause a hydraulic force to open the valve. As the element overheats, the electric circuit opens to keep the element from overheating too much. As the wax cools the electrical circuit is closed (connected) turning on the heating element. The wax expands more and the switch opens. This cycle continues to happen for the entire call for heat.

Some smart thermostats will sense the open circuit of this cycle as a fault.

In a Class I teach, we discuss the wiring of zones with zone valves, and this 3 wire zone valve is always a cause for discussion and concern. Most installer error wiring problems are on these valves because the #2 terminal is a common terminal. Common to the end switch and common to the actuator. There is a chance for 2 separate transformers to but heads, make back feed to cause valves to open when not calling for heat, or even try to make 48 volts when inadvertently become wired in series.

My questions are always "when did the problem start?" and "what was done just before the problem started?"

In one case a cable television installer was stapling wires in a basement and hit a thermostat wire. Since this was in the summer, the problem did not present for several months.

So was there any repairs completed recently? To the zone valves or the thermostats? or any other construction work? or did someone place a box near a wire that was inadvertently moved?

OR

Did leveling the thermostats resolve the issue?

HVACNUT

> @DrVetur said:
> Thanks @Jamie Hall. Leveled the mercury ones. No common wires unfortunately


The existing thermostats are using only 2 wires but is there one or more unused wire behind the sub base? We usually wrap unused wire around the sheathing.

Those zone valves simply twist and pull off.
Exercise the needle plunger. Don't damage it.

If that doesn't work,
Shut off the power and swap the zone valve with that of another zone.
Rewire so the thermostats continue to operate the zone they're supposed to.
Turn power back on and see if the problem recurs on the swapped zone.

If the issue is now on the swapped zone then it's a bad zone valve head.

If not, then its wiring or closed contacts on a relay.

Is there a zone valve zone control board?

EdTheHeaterMan

I'm hoping that my colleagues online will agree with this sequence of operation logic in this diagram.



On a call for heat, the end switch of any zone valve will operate the burner and the circulator for the heating zones. If the heating zones cause the boiler water temperature to fall below 160° (based on your 170° low setting and 10° diff setting) the space heating circulator will stop and the burner will continue to operate until the boiler water temp rises to 170°, allowing the circulator to operate again. this cycling of the circulator will continue until the return water from the heating zone(s) is high enough to keep the boiler temperature above 160° until the call for heat is satisfied.

This wiring logic will also bring on the burner on a call for hot water by way of the Taco Relay 4NO Terminal supplying power to the burner through the ZR terminal in the L8124A. This will operate the burner safely through the high limit control in the L8124a control. (currently, your wiring does not bring on the burner on a call for heat from the DHW tank.)

This may give reduce the DHW temperature droop you experienced in one of your previous tests.

This rewiring will get you in a better place and you don't need to purchase any new controls. If you are not comfortable doing the wiring, have a pro electrician or oil burner or HVAC tech do it.

Ed the Heater Man

P.S.
I would purchase a taco ZVC -4 or 5 to make zone value operation and troubleshooting easier in the future.

Zman

EdTheHeaterMan said:

P.S.
I would purchase a taco ZVC -4 or 5 to make zone value operation and troubleshooting easier in the future.

This would be my first step on this. Your zone valves will operate more reliably and be far easier to troubleshoot.

EdTheHeaterMan

I was wondering what the other zone in the picture was. The one with the 1-1/4” flo-valve? Then I saw @DrVetur’s other post on Domestic Hot Water. First thing I would do is the re-wire to see if the DHW problem is resolved. No additional parts needed

DrVetur

Thanks everyone. Looks like it was a leveling issue, but otherwise agree that the current setup is not optimal.