Thermostat Internal or Hidden Switch Setting FAQs

Q&A on How to Set Thermostat Cycle Rate Switches, Fan Switches, Emergency Backup Heat, Reset, inside of room thermostats

Which settings give the longest on-cycle on a Honeywell CT87K Thermostat?

Please just tell me which settings give the longest cycle on the CT87K On 2016-03-05 by Fred Gruber

Answer by (mod) - The length of heat-on cycle is affected by the heat anticipator

Fred:

If you have had trouble finding the manual for your Honeywell CT87K thermostat let me know by Email (see the page bottom CONTACT link) and I'll help you get a copy at no charge.

There you'll see that there are two internal switches that are to be set in this thermostat according to the type of heat it is controlling:

Steam heat: Switch 1 ON, Switch 2 ON

High Efficiency warm air (furnace) heat (90% efficiency or greater): Switch 1 OFF, Switch 2 ON

Gas or Oil warm air (furnace): both switches OFF - this is the Factory setting

Electric warm air (furnace): Switch 1 ON, Switch 2 OFF

There is also an internal FAN CONTROL switch in this thermostat

Set the INTERNAL Fan Control Switch inside the thermostat to F for Gas or Oil fired heating systems (this is the factory setting)

Set the INTERNAL Fan Control Switch inside the thermostat to E if your heat is electric or by a heat pump. As Honeywell explains,

"(This setting is for systems that allow the thermostat to control the fan in a call for heat, if a fan wire is connected to the G terminal.)"

There is no traditional heat-anticipator adjustment as was found on some older thermostats we describe in this article series.

So you cannot adjust the "on cycle length or duration" in the thermostat on those models.

How to adjust heat-on run time at my CT-3200 thermostat?

I'm using the Honeywell CT3200 wall thermostat to control a gas furnace, the heat system runned for four minutes & stop wait another 22 minutes to restart again.

How can I adjust the running time for about 10 minutes and retuning time ? On 2023-02-23 by charlie

Answer by InspectApedia Editor - On typical residential furnace controls you don't and can't adjust the run time as if there were a timer or clock: here's what controls "heat-on" time duration-

@charlie,

The theromstat does not have an explicit "heat on duration time" setting.

Rather, the thermostat acts as a simple "ON/OFF" switch as follows:

IF room temperature falls below the thermostat temperature setting and is set to "HEAT" then the thermostat turns your heater ON.

WHEN room temperature reaches the thermostat set temperature then it ends the "call for heat" and turns the heater OFF.

As long as the thermostat is calling for heat the fan will run and the burner may turn on and off depending on the temperature in the furnace itself .

So if you're not getting the heat that you want you may want to look at the air flow and start by being sure that the ducts are not crimped or disconnected and that you have a clean air filter installed.

In case you don't have your copy, please see the Owners Guide for your thermostat here

HONEYWELL CT3200 THERMOSTAT OWNERS GUIDE

Check the FAQs section towards the end of the owners guide for some possible steps to try. Specifically note:

~ Furnace cycles too often or system cycle length is too short or too long

~ Heating does not come on

If you're still having trouble, contact Honeywell support directly for assistance. Their contact info is:

CUSTOMER ASSISTANCE
www.honeywell.com/yourhome
Call Honeywell Customer Care at 1-800-468-1502.
Before you call, please have the following information available:
— Thermostat model number and serial code (located under the battery cover).
— Type of heating/cooling system (hot water, warm air, oil, gas, etc.).
— Number of wires connected to the thermostat.

On typical residential furnace controls you don't and can't adjust the run time as if there were a timer or clock.

Instead, the on and off cycling of the blower fan is controlled by the thermostat.

How do I adjust the “swing” setting on Honeywell RTH2300 wall thermostat

Hi
I’m using the Honeywell RTH2300 wall thermostat to control a gas furnace. Is there a way to adjust the “swing” setting on this particular thermostat?

Thanks On 2022-09-23 by Bob

Answer by InspectApedia-911 (mod) - set the thermostat to the type of heat you have and the fuel used.

@Bob B,

In programming mode, Advanced function number 5 allows you to specify the type of heating system that you have such as gas or oil and hot air or hot water.

Those adjustments have some effect on what you are calling the swing setting.

Here are two detailed procedures that are helpful examples of setting the thermostat's cycle or swing rate:

• THERMOSTAT CYCLE RATE SWITCHES - CT87: choose heating system type: Steam, Hot Water, Heat Pump vs GasOil/Electric Forced-air (Factory setting)
• THERMOSTAT SWING SETTING / CYCLE RATE - 3M-22 Filtrete

If you don't have the instruction manual for your thermostat you can find it at

THERMOSTAT INSTALLATION & WIRING MANUALS

where you will find free PDF download files of instructions for just about every thermostat including yours.

New CT87K thermostat installed; now the low voltage transformer blows up

I replaced Honeywell mercury stat with Honeywell ct87k. Cycle rate set switch 1 off. 2 on.

Runs couple days, then blows 24 transformer in boiler room.

When that happens the zone valve runs continually.

Has new white Rodgers 1311-102 valve. On 2022-03-24 by Gary Honeywell

Suggestions by Inspectapedia Com Moderator -

@Gary,

When I've found problems with burning up the low voltage transformer usually the issue has been tracked to

- shorted thermostat or control wires

- overloading the transformer (too many devices being supported)

- an under-sized transformer

Honeywell also warns that the CT87K is not the right replacement for every situation (If your HVAC system thermostat was using 4 or more wires you need a different model)

You probably already have it but if not the IO and Wiring manuals for your Honeywell CT87K are at

THERMOSTAT WIRING HONEYWELL

and for your White Rodgers 1311 zone valve the IO manual is listed as a PDF download at

ZONE VALVE MANUALS & WIRING

Should I leave my thermostat switch set to GAS/OIL or change it to ELECTRIC/HEAT PUMP?

The switch in the back of my thermostat what's recommended to leave on GAS/OIL or switch it to ELECTRIC / HEAT PUMP On 2021-07-13 by Oscar

Explanation & answer by danjoefriedman (mod) - set the thermostat switch according to your actual heating method

@Oscar,

How is your building heated?

Electric heat, or a fossil fuel like gas or oil, or by a heat pump?

You'd set the thermostat switch according to your actual heating method.

Don't worry too much about this setting: your thermostat will work in any event, but its accuracy in choosing exactly how to turn your heating system off will be improved if the switch is set correctly.

Let me know if this answers your question or post follow up questions if you like.

Should we set our thermostat to GAS/OIL or to ELECTRIC if we have oil fired forced hot air heat?

I wonder if it was set to electric because we have forced air to and in the winter it needs to be switched?

So if i have a fuel oil forced air furnace the tab on the back should be slid over to gas /oil? We bought the house and it was set on electric - On 2020-12-06 by Jeremy

Answer by (mod) - set your thermostat to GAS/OIL

Although it won't make a big difference I agree that if you have oil fueled heat than you would set the switch to oil.

How do we turn our room thermostat ON or OFF?

How do we turn on switch to on and off? On 2021-01-17 by Debbie

Explanation by danjoefriedman (mod) - how to turn HEAT or COOL (Air Conditioning) "ON" or "OFF"

Debbie,

Not every thermostat has internal switches that you need to change.

Some programmable room thermostats like the Nest can actually be set to OFF (or other modes) but many other simpler older thermostats like the traditional Honeywell round T87 thermostat have NO on-off switch.

So we need to start with the brand and model of your specific thermostats to know what switches it includes. You shouldn't need to turn any internal switch on or off simply to have heat.

You can "Force" your thermostat to "HEAT OFF" simply by turning it way down below the present room temperature.

For summer or air conditioning mode, you could set the thermostat set temperature to COOL OFF by setting it well above room temperature.

You can of course also completelty turn off a heating or air conditioning system by turning off its main electrical power switch but that's not something I recommend

The Honeywell CT87K is for Heat Only; the Honeywell CT87N is for both Heating and Cooling

In reply to Fred Gruber’s 6 March 2016 comment, it is stated that

the Honeywell CT87N thermostat is for 24V heating systems, and that

the Honeywell CT87K thermostat is for both 24VAC heating and cooling systems - that is, the K model controls both heating and air conditioning.

However, the owner’s manual seems to say that the K model is for heat only, and the N model is for both heating and cooling, which is the opposite of what was stated in your reply to Fred Gruber. Who’s correct, the manual or you? Or am I misinterpreting both you and the manual, if that’s possible?

Thanks!O n 2019-11-29 by Paul

Discussion by (mod) -

Paul

Thank you so much for important comment clarify which thermostat models provide which functions. I always start by trusting honeywell's documentation as the most accurate. I'll review our article with that in mind. Thank you for taking the time to write about this.

The Honeywell CT87N and the CT87K are often discussed together in the same Honeywell thermostat installation guide.

The current Honeywell CT87K is a heat-only thermostat - one of the simplest to install and use, typically wired with just two wires (red and white) to turn a heating system on and off.

The Honeywell CT87N thermostat can control BOTH heating and cooling.

Right on the instruction manual you will see that Honeywell says

CT87K (24 Vac heating systems) • CT87N (24 Vac heating and cooling systems) - shown below

I mis-spoke and have fixed that text. Thank you for careful reading.

The little switch under “fan on or auto” switch was switched in the gas but we have electric heat and A/C: What's the difference?

My AC/Heat unit operates on electric, but I just noticed the little switch under “fan on or auto” switch was switched in the gas position.

Even though my unit is electric. Is that a problem? What’s the difference if my house runs off electric. OOn 2019-03-06 by Joe -

Reply by (mod) - Is it a problem to leave the thermostat switched to "GAS"?

Joe it won't be a show-stopper regardless of which way the GAS OIL switch is set as you'll get heat in either case.

The difference in those settings is an analog to the heat anticipator on some other thermostat designs, and simply tries to adjust the thermostat to account for the probable speed with which the heater will respond on a call for heat, thus avoiding "overshoot" in which the heat continues to warm the building past the point at which the thermostat is satisfied.

by Joe

My AC/Heat unit operates on electric, but I just noticed the little switch under “fan on or auto” switch was switched in the gas position. Even though my unit is electric. Is that a problem? What’s the difference if my house runs off electric.

by (mod) -

Joe it won't be critical which way the GAS OIL switch is set as you'll get heat in either case.

The difference in those settings is an analog to the heat anticipator on some other thermostat designs, and simply tries to adjust the thermostat to account for the probable speed with which the heater will respond on a call for heat, thus avoiding "overshoot" in which the heat continues to warm the building past the point at which the thermostat is satisfied.

by Joe

So it doesn’t matter which mode it’s on if I have electric. Is it best for it to be on electric if I have electric or does it really matter overall?

by (mod) -

My best advice was in the previous comment that I posted.

Certainly if you like you could experiment to see what the duration of heat on seems to be when you switch between the different modes but are using electric heat.

Confused by heating terms: my boiler is not steam nor gravity; it's forced hot water

Forgot to say - I have a old boiler 2 wire setup. Neither Steam or Gravity sound correct to me. It`s hot water and it`s pumped around. The point is your average DIY guy maybe confused by terms given by techs who work on these everyday.

The Honeywell CT87K that Fred asked about is for heat only -on the front of the manual you will see which does what.

The manual provided is dual for N/K but they leave out words "hot water" in the ON ON first choice box -which maybe the confusion. Factory setting caused my system to short cycle in 5 minute cycles - try ON ON. On 2017-01-07 by John

Details by (mod) - Distinction among types of heat is important. Boiler, Furnace, Hot Water, Forced Air, Gravity, Steam, etc.

Thanks John. That note will help other readers.

Your distinction among types of heat is important. There's plenty of confusion to go around.

Many people use the term "furnace" as generic. With rare exceptions, a "furnace" is a forced-air heating system. A "boiler" is a hot water heating system.

"Boilers" are further subdivided into

hot water heating system boilers - hydronic heat (hot water circulates through heating pipes and radiators or baseboards or similar heat-emitting devices)
and

Steam heating systems - steam heat (steam circulates through pipes and radiators and condensate or condensed water from cooled steam returns to the boiler)

Hot water heating systems are further sub-divided into:

forced-hot water heat: a circulator pump pulls water around through the piping and radiators/baseboards
and

gravity-hot-water heat: no circulator pump is used, and hot water moves by natural convection (hot water tends to rise in pipes as it's less dense or weighs less than cold water, and cold water tends to fall in pipes - to return to the boiler).

People use the term "gravity" hot water or "natural convection" hot water heat for these older-type systems.

Usually a gravity hot water system will have larger diameter pipes so that enough heat can circulate through the occupied space.