Lennox Harmony Zone Control Starting Boiler when it Shouldn't

myqhenryt

Hi,
I have a two-zoned home with a Lennox Harmony connected to a Lennox CBX32MV-036 with one Honeywell TH8320WF1029 per zone. Heat is provided via a hot-water coil (on the air handler) connected to a Lochinvar WHN-110. The zoning and heating work well, no issues there. But when I have the heat disabled (via the thermostats) and set the fan to on or circulate to move air around the house, the boiler starts up and house starts heating up. Any thoughts out there why this could be happening?

Thx

EdTheHeaterMan

Depending on how the thermostats are connected to the air handler, and the air handler/thermostat internal wiring is configured and finally the interconnection of the boiler to the air handler, there is probably a back door in the wiring logic that is powering up the boiler when the G wire to the air handler is powered.

The Lennox Air handler is a variable speed, communicating, system. This means that if you had the Lennox communicating control in place of the Honeywell thermostat, you probably could not connect the boiler to this system. That said... the conventional thermostat wiring (using R for power C for common Y for cooling, W for heating and G for fan operation) is somehow sending a signal to operate the boiler.

I have had similar problems that I have resolved with an isolation relay. On one job I have installed 3 isolation relays on a zone thermostat to make sure the thermostat sub-base that has this back door connection between W and G when wired direct. This makes it positive that only the fan operate when the fan relay is powered, only the burner operates when the heat relay is energized and only the compressor operates when the cool relay is powered.

Some might say ..." don't use the fan on feature ... problem solved". Since you have the "High End" air handler, I can understand why you might want to operate the fan only from time to time. circulating air thru a premium filtering system, or keeping room temperatures even throughout a zone when there is no call for heat or cooling is the reason you purchase these high end variable speed systems.

To help YOU out please post pictures of the wire connection to the thermostat(s) the air handler(s) and the boiler. If you are not mechanically inclined to the point that you want to attack this yourself, you should call the original installer to see if they have any insight to the issue.

Since there is no mention of hot water duct coils in the Lennox installation manual for the air handler...will also need to know what powers the zone circulators that send the heat to the duct coils ... are there any water temperature controls on the air handlers that keep the blower from blowing cold air? They might delay the fan operation until the coils are filled with hot water.

There are several regulars on The Wall that can give input once we have more info (AND PICTURES) about your system.

GW

The stats should not be doing any dual fuel switching. The Harmony does this.

myqhenryt

EdTheHeaterMan said:

Depending on how the thermostats are connected to the air handler, and the air handler/thermostat internal wiring is configured and finally the interconnection of the boiler to the air handler, there is probably a back door in the wiring logic that is powering up the boiler when the G wire to the air handler is powered.

The Lennox Air handler is a variable speed, communicating, system. This means that if you had the Lennox communicating control in place of the Honeywell thermostat, you probably could not connect the boiler to this system. That said... the conventional thermostat wiring (using R for power C for common Y for cooling, W for heating and G for fan operation) is somehow sending a signal to operate the boiler.

I have had similar problems that I have resolved with an isolation relay. On one job I have installed 3 isolation relays on a zone thermostat to make sure the thermostat sub-base that has this back door connection between W and G when wired direct. This makes it positive that only the fan operate when the fan relay is powered, only the burner operates when the heat relay is energized and only the compressor operates when the cool relay is powered.

Some might say ..." don't use the fan on feature ... problem solved". Since you have the "High End" air handler, I can understand why you might want to operate the fan only from time to time. circulating air thru a premium filtering system, or keeping room temperatures even throughout a zone when there is no call for heat or cooling is the reason you purchase these high end variable speed systems.

To help YOU out please post pictures of the wire connection to the thermostat(s) the air handler(s) and the boiler. If you are not mechanically inclined to the point that you want to attack this yourself, you should call the original installer to see if they have any insight to the issue.

Since there is no mention of hot water duct coils in the Lennox installation manual for the air handler...will also need to know what powers the zone circulators that send the heat to the duct coils ... are there any water temperature controls on the air handlers that keep the blower from blowing cold air? They might delay the fan operation until the coils are filled with hot water.

There are several regulars on The Wall that can give input once we have more info (AND PICTURES) about your system.

Wow, thanks for all of this. I'm going to climb up into my attic later and take some pics.

myqhenryt

Here are some pics of the Harmony board and the board from the air handler.









I'm not quite sure if there are temp controls for the water coil. Next to the air handler board there are what appear to be some kind of delay unit as well as a relay of some kind.

The zone circulators are hooked up to a Taco switching relay. I believe that is connected to the Harmony control.

Something to note is that when the thermostat (with the heat disabled) set with the fan on, the boiler starts up right at 3 mins. When that happens, the heating LED does not light on the harmony board. So maybe something on the airhandler is triggering the boiler to fire?