Can anybody shed some light on the mode of failure I'm seeing in the larger Trane gas packs with the -0.2" WC combustion system? I've seen several relatively young units with an internally shunted combustion blower motor, making the motor run all the time (no, it's not a high temp trip - the circuit is closed). the motor assembly is easy enough to change out and set up, but the wholesale cost is rather high and the failure rate seems excessive especially when two of four units just over a year old have had failures on the same job. Ideas?