33 according to the manual is LIMIT OR FLAME ROOL-OUT SWITCH IS OPEN – Indicates the limit, rollout switch or auxiliary limit switch is open or the unit is operating in high heat only mode due to two successive low heat limit trips. Check for – Improper or misaligned limit and/or limit shield, Improper low heat gas input adjustment – Stuck high heat solenoid in gas valve.
They sent a service technician out to do further troubleshooting and he tried a new limit switch but it didn’t help. He was able to determine that the limit switch was tripping when the furnace cycled from High mode to low speed mode. His assessment was that there was inadequate air flow across the heat exchanger that is causing it to overheat.
Next week the original installer and the install manager are coming out to see what can be done to provide more air flow. My questions to any furnace installers out there are:
Should the installers have increased the size of the duct work in the garage that leads to the down stairs and upstairs registers and/or cold air return?
Is this something that is expected of reputable installers or do they just marry the new furnace to the existing duct work and assume all is well?
Is there are way to determine which part of the duct work is not providing enough CFM? My understanding is that it could be that the furnace is not getting enough cold air through the return or it cannot push out enough heat air to the registers. Can I determine which on is the problem?
What would you do to address this problem?
Thank you for any help you can provide.