Gas and Oil Home Heating Furnaces - Furnace short cycling

I have a Honeywell RPJ II furnace. The furnace will not maintain a constant temperature in our home. I have replaced the Thermostat, so I don't think that's it. The heat will turn on if I shut it off at the Thermostat and turn it back on, however; it will not reach the 72 degrees the Thermostat is set at. A guy I work with suggested I replace the Thermacouple. I am fairly handy and don't have a couple hundred bucks to drop on a service call. If anyone knows what could be causing this or anything I can try before I call in a service guy, I would appreciate it.

Other facts, furance will light, and blow hot air, it just doesn't run as long as it should, and will not go on based on the heat setting of the Thermostat.

Thanks,
Ryan

So are you saying it will run for a while then shut off and in order to get it to start again you have to turn it off then back on?

If that's what your doing it probably needs cleaned and safety checked, as it sounds like it's going off on a safety, and turning it off then back on is resetting it.

Yes, in order to get the furnace to run again, I turn it off at the Thermostat, and turn it back on again. I have the Thermostat set at 72, but we don't ever get to the temperature. The furnace will turn itself on and heat the house, however; it doesn't get to the 72 degrees, and sometimes lets the house get as cold as 66 degrees before it kicks on. It seems quite random actually, but I don't want to risk being without heat once winter hits here in Michigan.

So, your suggestion is to get it cleaned and serviced?

Thanks for your replies,
Ryan

If you've got a clean filter and no vents are blocked that's where i would start for sure.

I always reccomend a good cleaning at least every other year.

sealed combustion unit

-ignites and heats for approx 5 mins
-thermostat appears to be calling for heat....contacts are showing power from stat
-after 5 mins unit stops heating
-unit can not be recycled for hours...