Replies

1. 
   UncleDunc | Dec 17, 2003 09:48am | #1

   When my furnace was doing that, I replaced the old analog thermostat with a programmable and it went away. My gas bill went way down, too, because it was easy to set the temperature back when nobody was in the house.

2. 
   BillHartmann | Dec 17, 2003 07:34pm | #2

   Most like the thermostat anticipator is set to high. That is a little resistor (heater) in the thermostat that causes it to turn off early, because the furnace will continue to put out heat for a short period of time after the gas burner turns off.

   Overtemp cutouts will also do that. But that typcially would not fit your case with the unit working normally if set for a higher temp.

1. 
   toast953 | Dec 18, 2003 07:41am | #3

   Bill, are you talking about the "little dial" , that one will see if you pop the T-sat cover off??, I think, if I remember right, it either goes 1-5, or 1-10. I will check in to that maybe tomarrow. I'am in the middle of a remodel, working around, one of those types who are "nice", but real pushy. Come to think of it, tomarrow, probaly will be a real good time, load my tools up for the day, oh lets say arond 11:00 am, and just leave for the day, yes that is looking better and better, just one more little nudge and I'll go adjust the  T-state anticipator. Thanks Uncledunc, and you Bill, and all the rest who make this forum, so enjoyable for this hack, whoops, I mean hammerhead. Jim J

1. 
   BillHartmann | Dec 18, 2003 04:49pm | #4

   Yes, that little dial.

   But when you are there look for something else. See if the fan comes on.

   Those units are often fairly cheap. And I am thinking that they fan might be going bad and the bearings are gummed up. With the low temp setting the furnace keeps cycling because fan does not run and the over temp cuts it off.

   At the higher temp the grease in the bearing are loose enough for it to run.

   I very, very seriously doubt that this is the case with that small a difference in temps, but there have been stranger problems.

1. 
   rjw | Dec 18, 2003 06:37pm | #5

   I really enjoy reading information like that! It is great to see what experts are thinking about and come up with!

   And my clients sometimes can't understand why, as a generalist home inspector, there are times I can't give them a definitive diagnosis and tell them to check with an expert!

   _______________________

   Tool Donations Sought

   I'm matching tool donors to a church mission to Haiti - we're shipping a bus converted to a medical facility in January (we hope) and can fill it with clothes, tools and all sorts of stuff needed in that poorest of all countries. A few hand tools or power tools can provide a livelihood for an otherwise destitute family. Please email me if you have tools to donate.

   Thanks to Jeff and David and Jim for their offers!

1. 
   BillHartmann | Dec 19, 2003 03:52am | #6

   Hardly an expert.

   Just a combination of experiences with several difference types of furances and heaters over the years.

2. 
   toast953 | Dec 20, 2003 08:47am | #7

   Bill, I made it over there today, I popped the T-stat cover off, grumbled about needing glasses, and I saw that the "little dial" was set right at 8 or 9, so I moved it to 4. thanks again. Could you explain just how that t-stat anticipator is supposed to work. Jim J

1. 
   BillHartmann | Dec 20, 2003 07:37pm | #8

   They are a small heater. They are suppose to be set according to the current draw of the gas valve. It has been a while since I messed with one, but the one that I remember was marked in amps.

   The idea is that that the furance continues to put off residual heat for several minutes after the gas valve shuts off.

   So the anticipator heats the thermostat up slightly so it will shut off just before the room reach the setpoint temp.

   In control logic that is called feedforward control.