Affiliate links may earn us a commission. As an Amazon Associate I earn from qualifying purchases. Affiliate disclosure

York 4 red flashes: The main limit switch has opened its normally closed contacts

Source: York manual (PDF) (opens in a new tab) ↗ · Updated

Status code4 red flashesYork
What does York 4 red flashes mean?

The main limit switch has opened its normally closed contacts. The control runs the supply air blower and the inducer while the limit stays open.

Homeowner part this code names: furnace air filter.

Search on Amazon

Opens an Amazon search for that name. Check the size against your manual. As an Amazon Associate I earn from qualifying purchases.

Call a pro: jump to when to call a pro Equipment type: furnace
How it shows: LED behind the blower-door view port on a York TG9S. Each flash is 1/3 second on and 1/3 second off, then a 2-second pause: 4 red flashes

York TG9S 4 red flashes means the main limit opened. The blower and inducer keep running while it is open. The manual lists a dirty filter, duct size, blower speed, firing rate, loose limit wiring and a faulty blower motor. If the limit is still open after five minutes, the control goes to a hard lockout and 11 red flashes. Five openings in one call for heat stay on 4 red flashes and add a one-hour soft lockout. Change a dirty filter with the power off. Call if it returns.

Likely causes

  • Dirty filter
  • Improperly sized duct system
  • Incorrect blower speed setting
  • Incorrect firing rate
  • Loose limit switch wiring
  • Faulty blower motor

Safe checks for 4 red flashes

  1. With power off at the furnace switch, check the filter and replace it if it is packed with dust. Use the size printed on the old filter
  2. If the limit has not closed within five minutes, the manual says the control assumes the blower is not functioning, starts a hard lockout, and flashes 11 red flashes. Power has to be cycled after that problem is corrected
  3. If the main limit opens five times in one call for heat, the control still shows 4 red flashes and enters a one-hour soft lockout
  4. Techniciancheck duct size, blower speed, firing rate, limit switch wiring and the blower motor
Safety firstIf you smell gas, do not touch any electrical switch or use a phone in the building; leave immediately and call your gas supplier from outside. Turn off electrical power at the furnace switch or breaker before opening any panel, and never bypass or jumper a limit, rollout or pressure switch. Gas valve, burner, venting, wiring and control-board work should be done by a licensed HVAC technician.

Capacitors can hold a charge after the power is off. Safety terms.

When to call a pro

Call a licensed HVAC technician if 4 red flashes return after a filter change, or if the light changes to 11 red flashes.

Email me this fix

We save your email and this page. Nothing is emailed. We'll only use your email for this request.

Privacy. Deletion requests go to the address on that page.

Request a filter and maintenance reminder

We save your email, this page, and the interval you pick. Nothing is emailed. We'll only use your email for this request.

Privacy. Deletion requests go to the address on that page.

Parts & tools for this fix

Taken from this code's causes or steps. A search link opens Amazon results and does not confirm a fit. Check the model number in the manual.

Furnace and AC air filter: guide

In this code: Dirty filter

Filtrete 16x25x1, 4 filtersFiltrete 20x25x1, 4 filtersSearch: York furnace air filter

Furnace blower (circulator) motor: guide

In this code: Incorrect blower speed setting

This one is for a technician to test or replace, so we only explain it and do not link to buy it.

High limit and rollout switches: guide

In this code: Loose limit switch wiring

A safety device: we explain it but do not link to buy one.

As an Amazon Associate I earn from qualifying purchases.Affiliate disclosure

Related York codes

11 red flashesThe main limit switch has opened10 red flashesThe gas valve is energized with2 red flashesThe pressure switch is closed when3 red flashesThe pressure switch contacts are open7 red flashesThe flame could not be established6 red flashesWhile the furnace was operating, the

All York codes →Browse every code