I have a Modine PD 30AA0111 in my garage.

It heats just fine but the blower only works some of the time, very rarely. I set the thermostat to fan "on" and waited about two minutes and nothing happened. So I replaced the thermostat. The blower worked once when I first installed the new thermostat but hasn't worked since so I don't think the problem was with the thermostat.

Any idea what I should try next?