I am having a huge issue with my furnace that heats my garage. As stated it's a Lennox G24M. The issue we are having is that is flipping it's primary limit switch after a short while. We have measured the heat at the heat exchanger (170 degrees) and in the plenum(92 degrees). There seems to be too much heat being held at the heat exchanger and not being pushed up into the plenum and along the duct work. We have checked the heat exchanger for damage and found none(looks like new), the furnace is approx. 5 years old. The chimney is clear and to spec., the vent motor is working correctly, the rollouts are working too,we have also checked the air flow capabilities in and out for correct capacities(all good), we have correct gas pressure as asked for in manual, primary cut off switch works correctly too cutting out at 170 degrees. The flame looks perfect too, nice and blue non flickering. We have vacuumed out all tubes in the heat exchanger for obstructions and found none. Physically checked heat exchanger and found nothing out of the ordinary. The blower motor working fine and on high at the moment, we have tried all settings there too.
So....why aren't we getting enough heat into the plenum? We have checked for obstructions everywhere and found none. The issue is that we have plenty of heat around the heat exchanger but not enough above it and can't figure out why.
Anyone have any ideas or suggestions???
The cold weather is coming and I need heat soon.
Thanking you in advance