Thermostat off in degrees

[djw2112]

My Duo-Therm thermostat is 5 degrees off.  When i set the heater for 65 it does not come on until 60 deg, is this fairly normal for them to be this far off the mark.  Can they be adjusted?

 

[Gary RV_Wizard]

No, not normal. What model thermostat and what types of heat?  Are we talking furnace or heat pumps?  Single zone or multi?


For a heat pump, it is is normal that the furnace doesn't kick on unless the heat fails to hold the set temperature.


For a multi-zone system, the actual temperature sensors are remote to the thermostat itself.  If a remote isn't reading or is defective, the results can be weird.

 

[Isaac-1]

Without knowing which model thermostat you have this is a hard one to answer, though having said that it is not normal.  Have you confirmed that it is not being effected by some heat source behind where it is mounted?

 

[kdbgoat]

Without knowing which model thermostat you have this is a hard one to answer, though having said that it is not normal.  Have you confirmed that it is not being effected by some heat source behind where it is mounted?

Good advice^^^^
On our fifth wheel, main t-stat is located on a hollow interior wall. Heat from the converter rises straight up that wall, and may cause the t-stat to think it's warmer than it really is. The common fix is to pop out a set of switches below the t-stat, and put some foam in the cavity of the wall, then pop the switches back in.

 

[John From Detroit]

First there may be an adjustment..  (I do not know) depending on the type of T-Stat

2nd.. A Brother P-Touch can make a label reminding you to set the thing 5 degrees higher than you want.  DAYMO makes a product that can do it as well.

 

[cavie]

as long as you know it 5 degrees accost the board what is the problem?, Same thing with my motorcycle speedometer. If I want to drive 65 I put it on 70. If I want 35 I put it on 40. No problems.

 

[djw2112]

All good advice, the problem is not it going off per say because yes it is in a bad location right above the heater vent.  The problem is when it comes on is the bad part, that is what i am doing now is just adjusting it 5deg from what i expect.

I wish i could provide a model number because it does not have one and i cant get it off the wall.

UPDATE:  got the cover off, the number is 3107612-008

They probably were more concerned with cooling than with heating which is why they put it there on the wall.

 

[Isaac-1]

Ah the Duo-Therm "analog" thermostat, I replaced mine with a modern Honeywell battery powered thermostat when my analog thermostat started doing wild temperature swings between off and on, making it hard to sleep.  Think cover up with blankets, heater comes on, you get hot, kick the blankets off, heater cuts off, you get cold, you think the heater will come on soon, you get colder, you cover up, and then the heat comes on, repeat.

There are numerous instructions online for how to replace one of these with a modern Hunter or Honeywell branded thermostat, though there are a few words of caution:

1, the wiring instruction in the box are useless on this retrofit since RV's use a different switching logic (ground switching)

2, Pay attention to the wire color (take a picture before you disconnect anything), not everyone uses the same color coding.

3, You will have a left over positive wire that should be taped up and isolated since the new thermostat is battery powered

4, You may want to add a separate hi/lo fan switch in, as these thermostats don't have on, I added one into the side of my thermostat using a cheat toggle switch, though I did have to remove a few of the plastic ribs in the thermostat to make it fit.

See https://www.youtube.com/watch?v=lOPtLUTmHIc for one of many marginal videos showing how to do this

also see https://www.youtube.com/watch?v=yVPgAqinM3k

Here is a write up that includes a wiring diagram http://www.modmyrv.com/2012/01/03/mod-100-honeywell-digital-thermostat


p.s. finally here is a picture of mine with the hi/lo fan switch mounted on the left side of the thermostat using a 25 cent ebay switch with pigtails

 

[BIG JOE]

I use the numbers on our Dometic T-stat for reference only. We set it a 75.. it keeps the Heat temp at a comfortable 70*. For A/C we set it at 80.. keeps it at a comfortable 76/78*.

 

[Gary RV_Wizard]

The slider on that analog thermostat is not very accurate, so maybe I should rescind the opinion that yours is "not normal". 

There are various options for replacing it with a digital model. You Tube has several how-to videos or you can Google "DuoTherm analog digital upgrade" and find some articles on the subject.

 

[djw2112]

Thanks everyone, ill add it to the project list

 

[timjet]

I had an issue with my temp controller reading several degrees off. I found the sensor and cleaned it with a feather brush. That seemed to make the controller read more accurately.