Heil furnace Heartbeat: Normal operation — standby or a call for heat
A steady pulse rather than a count means the SmartValve is powered and working. It covers both standby and an active call for heat, so it does not tell you whether the furnace is currently running.
Applies to: International Comfort Products *9MPT and *9MPV gas furnaces using the Honeywell SV9541Q SmartValve, sold as Heil, Tempstar and Comfortmaker. The diagnostic LED is on the gas valve itself. Furnaces that diagnose through the control board use a different code table.
What it means
The SmartValve uses a heartbeat — a continuous slow pulse — to mean normal operation. It is not a count and should not be counted. What makes this heartbeat slightly different from other manufacturers' is its scope: ICP documents it as covering both standby and a call for heat, so the same indication appears whether the furnace is idle or actively heating. That means a heartbeat tells you the valve's control is healthy, and tells you nothing about whether the furnace is doing anything. If the house is cold and the valve is showing a heartbeat, the fault is upstream — the thermostat, the wiring, or the furnace control that decides when to call.
Most common causes
- The SmartValve is powered and has no fault to report. This is the intended meaning.
- The furnace is in standby with no call for heat.
- The furnace is actively heating. Both states show the same indication.
How to diagnose it
- Distinguish a heartbeat from a flash code by rhythm. A heartbeat pulses continuously; a code is a sharp on-off pattern with a pause before it repeats.
- Note that this indication does not distinguish standby from heating, so use the burners or the blower to tell what the furnace is actually doing.
- If the house is cold and the valve shows a heartbeat, check the thermostat before anything else — set to heat, above room temperature, and with fresh batteries.
- Confirm you are looking at the gas valve LED and not the control board. They report different things.
How to fix it
- Nothing to fix if the furnace is heating normally.
- If the house is cold, correct the thermostat setting or replace its batteries.
- If the thermostat is calling and the valve still shows only a heartbeat with no burners lighting, that is a fault upstream of the valve and needs a technician.
- Do not start pressing switches on the gas valve. The on/off switch on an SV9541Q in the off position during a call for heat produces its own diagnostic code.
Notes
Knowing what your own furnace shows when it is healthy is worth the minute it takes to look. A heartbeat means nothing useful if you do not know it was doing that last week too.
Related
- Which diagnostic system you have — Heil, Tempstar and Comfortmaker furnaces use two different code systems that contradict each other
- LED off — The control is not powered
All codes for this manufacturer
Heil, Tempstar and Comfortmaker furnace codes — every code, with what differs between models.
Related signal patterns
More signals like this across brands: normal operation signals.
Related signal patterns
More signals like this across brands: normal operation signals.
What this looks like
From the outside, this usually shows up as there is no heat but nothing looks obviously wrong — that walkthrough covers what to check in order, and when it stops being a homeowner job.
What the fix costs
A heartbeat itself needs no repair — its value is in where it lets you stop spending. Because this LED is on the gas valve, a healthy pulse clears the valve's own control and pushes the search upstream: thermostat, low-voltage wiring, or the furnace control board that decides when to call for heat. That routing matters financially. The repair guide prices a thermostat at $150–400, and the board cost guide puts a control board at $400–900 — the part a cold-house, healthy-valve investigation eventually reaches, and one worth that guide's skepticism before anyone condemns it.
Do it yourself or call someone?
Homeowner-safe: confirm you are looking at the valve's LED and not the board's — this brand runs two code systems, and the distinction decides which table applies — then run the thermostat basics: batteries, heat mode, setpoint above room temperature. If the thermostat is calling and the valve still shows only an idle heartbeat, something between them is not passing the message; that is meter work on the control circuit and the point to book a visit. A heartbeat with a warm house needs nothing at all.
The same signal on another control
Allied's -02 control also idles on a heartbeat, but a narrower one — documented at exactly one second on, one second off, and checkable against a watch (Allied heartbeat). ICP's covers standby and active heating alike, which is why it confirms less about what the furnace is doing.