Heat tests good but stops after tech leaves

Hello
Do you have any error codes ? If not you could have many possibilities from a Clogged lint screen, restricted vent system, thermistor issues, gas valve dropping out, main PCB defective, Software Version not up to date . See technician diagnostics sheet link below and testing procedures below. Matt Ace technician

Service Mode
Press Mixed Load Bell + Temp for 3 seconds in normal mode
until it sends out a beeping sound
If pressing same combo of buttons it will leave this mode

Software Version Test Mode
How to Enter:
Press Temp key for 3 seconds (until beep)
Note: ex) In case of “U105” U0 means major version “v1”
05 means version “05” If press Temp key in software version
mode it will return to Service Mode

Gas Valve Testing
Unplug connectors and test valve terminals
(its numbering is from the front terminal.)
Check across terminals #1 and #3 (Booster Coil). 550 Ω
Check across terminals #1 and #2 (Holding Coil). 1350 Ω
Check across terminals #2 and #3 (Both coils in series). 1900 Ω
Check across terminals #4 and #5 (Secondary Coil). 1300 Ω

Moisture sensor & Thermistor
CN4 – On control board
3-6 Thermistor 1 (Blu-Red)
4-5 Moisture Sensor (Pnk-Org)

Hi. I have attached the service manual for this unit. Has the machine given any error codes? You will find the error codes in the manual. I do not see a way of going into diagnostics to retrieve any stored errors. I would check your thermistor for proper resistance. Also, check for a loose power cord or outlet that may be losing voltage. Check for proper power and check the power cord at the terminal block for loose or burnt connections. If everything checks out good, you may have a faulty control board. check for burnt marks on the board especially at the heat relay.