Modine HD60 HotDawg Heater Issue

[dshanahan]

I am having and issue with a Modine HD60AH0134 natural gas hot dawg heater. The unit will power on, pre-purge fan start and sound good, I can see that the green light on the gas valve flashes bright then dim then bright then dim which I believe is normal operation. Once the hot flame ignitor turns on the gas valve opens and the burner will light, all 4 burners light and the flame sensor is in the flame correctly. Approx 5-10 seconds after the burner lights it will shutdown, the purge fan continues to run. This sequence will continue for 6 cycles and then the unit will lock out.... I am not able to find and type of bad sensor or safety.. .Can you advise on what the issue could be.. or can you provide some trouble shotting steps.

I have confirmed that the flame sensor is good and that the polarity is correct

Anyone have any thought on what could be my issue?

Thanks
Dave

 

[fitter30]

Found this. It may be the pressure switch. If you jumper wire with alligator clips after combustion fan starts jump it out see if it stays running.

https://www.google.com/url?q=https://www.modinehvac.com/wp-content/uploads/2020/01/HD_Troubleshooting_Guide_6-586-1.pdf&sa=U&ved=2ahUKEwiHqquhhaKRAxVW1fACHQKRE7UQFnoECAgQAg&usg=AOvVaw1fODJoL3drEOsRxQpdBycq

 

[dshanahan]

Thanks for the help, I ended up finding the issue was a blocked tube from the purge fan to the pressure sensor, clear that out and I am good to go...