There is a small light on your thermostat that most Venice homeowners never think about — until the electric bill arrives. Labeled AUX, AUX HEAT, or EM HEAT depending on the thermostat, it tells you when your York system’s electric heat strips are running. Learning to read that light is the single most useful skill for managing heating costs: it distinguishes normal backup operation from a system burning money. This page is the homeowner’s guide to what the light means, what normal looks like, and when it is telling you to call.

What the aux light means

On a heat pump system, the electric heat strips are the backup singers — they step in when the heat pump needs help. The AUX HEAT indicator lights when the strips are actively supplementing the heat pump: during very cold weather or when the thermostat detects the heat pump falling behind the setpoint. This is normal, designed behavior — the strips exist for exactly these moments. EM HEAT (emergency heat) is different: it is a manual thermostat mode that locks out the heat pump and heats only with the strips. Emergency heat is for genuine emergencies — the outdoor unit has failed — not for everyday use, because it heats at roughly three times the cost of heat pump operation. Knowing which light you are looking at, and in which mode, is the foundation of everything below.

What normal looks like

Normal aux operation has a pattern. On the coldest Venice nights, the AUX light appears during the coldest hours and disappears as temperatures moderate — the strips helping the heat pump across the hardest part of the night. It should not be on constantly through mild weather, it should not be on when the house is already at setpoint, and EM HEAT mode should never be engaged unless the outdoor unit is genuinely out of service. If your system’s behavior matches this pattern, the strips are doing their job and your bills reflect real heating demand. If it does not match — the light that never goes out, the EM mode someone switched on months ago and forgot — the strips are no longer backup. They are the bill.

When the light means trouble

Several failures announce themselves through the aux indicator. Aux on constantly in mild weather: the heat pump is not carrying its load — possibly an outdoor unit problem, low heating capacity, or a control fault — and the strips are compensating. House overheating with aux lit: a sequencer stuck closed, keeping a strip bank energized regardless of demand; the thermostat is satisfied but the heat will not stop. Aux never appearing on the coldest nights: the strips are not available when needed — failed elements, failed sequencers, or tripped limits — and the heat pump is struggling alone. EM HEAT engaged unknowingly: someone switched the thermostat to emergency heat during a past issue and never switched back; the system has been heating at triple cost ever since. Each of these deserves a service call, and the sooner the better — every day of inappropriate strip operation is money converted directly to heat you did not need.

What the technician checks

When you call about strip behavior, the visit is an electrical investigation. The technician verifies the thermostat’s mode and wiring — is the system calling for aux appropriately, or is a control fault manufacturing the call? Each strip bank’s element is measured for correct resistance; open elements and shorted elements are identified bank by bank. Sequencers are tested through their full staging cycle: do banks energize in sequence on demand, and — critically — do they de-energize when satisfied? Amperage draws per bank are measured against ratings. And on a heat pump system, the outdoor unit’s heating performance is checked too, because strips compensating for a struggling heat pump are a symptom with a cause elsewhere. This is purely electrical diagnostic work: meters, resistance readings, and staging tests — no sealed-system work involved.

What replacement and repair look like

Failed elements, stuck sequencers, and faulty controls are replaced with genuine York parts installed by trained technicians — power verified off and locked out, connections torqued to specification, and the full staging sequence proven before the visit ends: banks on in order when called, banks off when satisfied. Thermostat misconfiguration is corrected and explained so it does not recur. If the investigation found the heat pump itself struggling, that finding comes with its own diagnosis and options — because fixing the strips without addressing why they were overworked just restarts the clock. Every repair is verified under real operating conditions, and the visit documentation goes into your home records with the rest of the system’s history.

Reading the light from now on

Make the aux indicator part of your winter awareness. Glance at the thermostat on cold mornings: is AUX behaving as described — appearing in the coldest hours, disappearing as the day warms? If the pattern changes — the light that used to cycle now stays on, or appears in weather that never used to trigger it — call before the bill arrives, not after. Keep filters changed on schedule, because restricted airflow overheats elements and trips the safety limits that protect them. Keep the annual service visit, whose electrical inspection covers exactly these components. And for the urgent cases — strips that will not shut off, a burning smell from the air handler, a breaker tripping on the strip circuit — our 24/7 emergency service with same-day dispatch covers Venice around the clock. Electrical faults never improve with waiting.

FAQs

What does AUX HEAT mean on my thermostat?

It means the electric heat strips are actively supplementing the heat pump. Occasional aux operation in cold weather is normal; constant aux in mild weather is not.

What is the difference between AUX and EM HEAT?

AUX is automatic backup the system engages as needed. EM HEAT is a manual mode that locks out the heat pump and heats only with strips — for genuine outdoor-unit failures, not daily use.

Why is my aux light always on?

Common causes: the heat pump not carrying its load, a stuck sequencer, a control fault, or EM HEAT mode left engaged. All deserve a prompt service call.

Can I just leave EM HEAT on?

No — it heats at roughly three times the cost of heat pump operation. Switch back to normal heat mode and call if the system will not heat properly without it.

Is a burning smell from the vents an emergency?

Yes. Turn the system off and call immediately — our 24/7 emergency service with same-day dispatch covers Venice around the clock.