No heat!, light blinks 3 times

Contact Leviton direct. They will know if the fan or sensor is faulty or it is the control that is faulty?

https://www.leviton.com/en/products/residential/fan-controls/fan-speed-controls/humidity-sensor-fan-control

..

How you need to do the same with the pressure switch

TRI-COLOR (DSI LED) DIAGNOSTIC TABLE
No. of Red BLINKS
1 Flame sensed when no flame should be present
Verify the gas valve is operating and shutting down properly. Flame in burner assemble should extinguish promptly at the end of the cycle. Check orifices and gas pressure.

2 BLINKS Pressure switch stuck closed/ inducer error
Pressure switch stuck closed. Check switch function, verify inducer is turning off.

3 BLINKS 1st-stage pressure switch stuck open/inducer error
Check pressure switch function and tubing. Verify inducer is turning on the pulling sufficient vacuum to engage switch.

4 BLINKS Open limit switch Verify continuity through rollout switch circuit.

5 BLINKS Open rollout/open fuse detect Verify continuity through rollout switch circuit, check fuse.

6 BLINKS 1st-stage pressure switch cycle lockout If the first stage pressure switch cycles 5 times (open, closed) during one call for heat from the thermostat the control will lockout.Check pressure switch for fluttering, inconsistent closure or poor vacuum pressure.
7 BLINKS External lockout (retries exceeded) Failure to sense flame is often caused by carbon deposits on the
flame sensor, a disconnected or shorted flame sensor lead or a
poorly grounded furnace. Carbon deposits can be cleaned with
emery cloth. Verify sensor is not contacting the burner and is locatedin a good position to sense flame. Check sensor lead for shortingand verify furnace is grounded properly.

8 BLINKS External lockout (ignition recycles
exceeded where flame is established and then lost)Check items for exceeded retries listed above and verify valve is not dropping out allowing flame to be established and then lost.

9 BLINKS Grounding or Reversed polarity Verify the control and furnace are properly grounded. Check and reverse polarity (primary) if incorrect.

10 BLINKS Module gas valve contacts energized
with no call for heat Verify valve is not receiving voltage from a short. If a valve wiring is correct and condition persists, replace module.
11 BLINKS Limit switch open - possible blower
failure overheating limit Possible blower failure, restricted air flow through appliance or duct work. Verify continuity through limit switch circuit and correct overheating cause.

12 BLINKS Module Ignitor contact failure Fault code indicates the module ignitor contacts are not functioning
properly. Replace module.Solid Module - internal fault condition Module contacts for gas valve not operating or processor fault.
Reset control. if condition persists replace module.
3 double 2nd-stage Pressure Switch Stuck Open/Inducer Error
Check pressure switch function and tubing. Verify inducer.

The pressure switch requires a negative pressure (vacuum) to close the contacts. It is measuring the pressure in the inducer and indirectly ensure there is good combustion airflow throught the heat exchanger. Check for a small vacuum, in the neighborhood of 1" water column. Usually the vacuum required to close the switch is stamped on the vacuum switch. Check the vent pipe for obstructions and correct size and installation.
If the pressure aka vacuum switch does not close the furnace will not continue with ignition, for safety reasons.

could be the pressure switch not working or the hot surface igntior not working

Your preasure switch is closed

Do you have the code reference on your furnace door? If so what does it say? The furnace has locked itself out, and we need to determine what in the world it needs..

the pressure switch is closed before the draft motor closes it.the board is telling you that this is not right.pull the wire(either) off of the pressure switch to see if furnace tries to light.if it does,you should replace the pressure switch.

A constant red light (not blinking) indicates that the thermostat is not calling for heat. Of course you know it is but just to be safe, jump out R and W on the board. If it continues to do the same as you indicated, replace the board.

If your heater is like mine...

There is a small window about the size of a quarter inside

the panels on the front part of the heater.

The panels must be removed to see it.

It might look like a hole but glass is there.

Inside the window an L.E.D. light might be blinking.

If this is the case, count how many times its blinking.

the number of blinks represents the nature of the problem.

 

if it blinks 3 times its possibly either a small outflow fan isn't working or something is blocking the vent which prevents a flow detector from making contact.

The reason it shut down is because of the fear of carbon monoxide poisoning due to no ventilation.

Try looking into the vent pipe from the top of the roof to see

if there are any obstructions.

If there are no objects blocking the vent pipe then maybe a fan or transformer has malfunctioned.

The light blinking 3 times refers to the combustion air switch.

It works as a vacuum chamber to work the contacts inside it.