Harman PF120 issue with 4 blinks using thermostat

[Rayterio666]

I have the furnace for 2 yrs now and always been on an Honeywell T5 thermostat and worked like a charm, but for the last 3 days, my status light blinks 4 times and then the stove does not shutoff, but goes on until it runs out of pellets... did not change anything, any ideas what is going on?

Tks

 

[DAKSY]

From Harman:

4 Blinks: Can occur only in the Automatic Mode and
indicates the Wall Control has failed or is not installed. If a
Wall control is then installed the status light will automatically
reset.(Note) only after the unit has warmed up.

Sounds like your t-stat is on it's way out, or there's a connection problem...

 

[Connecticut Yankee]

. . .
Sounds like your t-stat is on it's way out, or there's a connection problem...

Forgive a noob question, but could this also result from t-stat batteries running down? Inquiring minds want to know!

 

[DAKSY]

Only one way to verify...

 

[Rayterio666]

Trust me guys, there is no stupide question!
My T5 is powered via a12 volts transformer, same type as a doorbell transformer.
I tried another non-WiFi thermostat I was using before this one with no issues when I changed it, same results, I even tried Harman’s analog thermostat that came with the furnace and still the same issue.... see pic.
Now I am guessing either the control board ( which is kinda expensive to replace) or the ESP probe...
Any thoughts, idea will help me
Tks a million