York furnace Green heartbeat: Normal operation, no call for heat, no active errors

A steady green heartbeat means the board is healthy and idle with no active errors. If the house is cold and the light is beating green, the furnace has not been asked to run.

Applies to: York, Luxaire and Coleman gas furnaces using the UTEC integrated furnace control boards documented in technical service letter ST-045-09.

What it means

York's UTEC boards use a heartbeat pattern rather than a simple on or off, and green means idle with no active errors. That is informative when the house is cold, because it eliminates a great deal: the furnace has power, its safeties are satisfied, and nothing is currently faulting. What remains is that no call for heat has arrived. The call comes from the thermostat over the low voltage wiring, so a cold house and a green heartbeat point at the thermostat, its wiring, or its power — not at the furnace. Note that a green heartbeat says nothing about stored faults, which have to be replayed deliberately.

Most common causes

• The furnace is idle and everything is normal.
• The thermostat is not calling for heat — set to cool, set to off, or set below room temperature.
• The thermostat's batteries are flat.
• A break in the low voltage wiring between the thermostat and the furnace.
• A thermostat that has failed or lost its programming.
• A thermostat wired incorrectly after replacement.
• A zone control board not passing the call through.

How to diagnose it

1. Check the thermostat is set to heat and above the current room temperature.
2. Replace the thermostat batteries if it takes them, even if the display looks normal.
3. Note whether the thermostat shows a call-for-heat indicator. A thermostat that thinks it is calling and a board showing idle means the signal is not arriving.
4. Check whether the blower runs on the fan-on setting — fan working and heat not points at the heat wire.
5. Remember that a green heartbeat does not mean no faults have occurred; the stored history has to be replayed separately.

How to fix it

1. Correct the thermostat setting or replace its batteries.
2. If a thermostat was recently changed, have the wiring checked against the furnace's terminals.
3. Low voltage wiring faults and zone control problems are technician work.
4. Ask the technician to replay the stored fault codes even if the board is showing a healthy heartbeat, since an intermittent fault will not be visible any other way.

Notes

The distinction between an active state and a stored history matters on these boards. A furnace showing a green heartbeat has faulted five times this week if the history says so, and nothing about the current indication would tell you.

Related

• Fault code retrieval — How to read and clear stored fault codes
• Amber heartbeat — Normal — call for heat

Sources

• Johnson Controls Unitary Products technical service letter ST-045-09 — York UTEC furnace boards, fault code tables and retrieval procedure