Hi:
I have a 60k btu natural gas Modine Hot Dawg garage heater with a hot surface ignitor. When the wall thermostat calls for heat the HSI will glow, the burners will fire, fans come on (exhaust and circulator), burners run for about 4-8 seconds and then cut out. Fans stay running as the furnance will attempt to refire. Sometimes it stays lit for the cycle, sometimes it tries 4-5 times short cycling and then goes into lockout and needs to be powered off to reset.
I have replaced the flame sensor, switched the AC polarity (recommended to try by Modine), and bypassed the limit switch to rule those out. It has 2 flame rollout switches and neither are tripped. The limit and rollout switches are in series on the same circuit and all have continuity when checked by a meter as this nonsense is going on. The unit is clean inside and the flue is not blocked.
Thoughts? What am I missing?
Thanks
BG
