Nest Thermostat furnace short cycling

[richmaz]

I just installed the thermostat and I have c wire correctly installed.  The furnace will heat for about 6-7 mins and then cycle down and cycle back up to heat again for another 6-7 mins.  It won't reach the desired heat setting in one cycle.  There are no error message displayed or any loss of power.  Please help. 

[kennedmh]

Same issue here.  It's taking more than two hours for my house to come up to temp in the morning because of the short cycling, not to mention the increased wear and tear on my furnace.  C wire is connected and I don't get any battery messages or complaints from Nest that there's a problem.

Any idea, Google?

Matt

[fedino82]

Same here with the Nest telling me that the furnace shuts down every 15 mins and to check filters. The furnace does show an overheating error / limit circuit fault code 33.

I changed the filters and had the furnace checked by a technician: he had the furnace running for 2 hours and never stopped nor give an error code.

I then removed the thermostat and connected red and white wires: the furnace works continuously, never stops and no error code.

Hence, this error is caused by the thermostat.

[Lizzyf]

I am having the same problem. I’ve changed the filter and after restarting it worked great for an hour. But then seemed like the house was too hot even though it wasn’t set higher. Now it’s back to the same thing. 

[Mike737]

Where are the replies to the above queries?  I'm also having these issues.

[kennedmh]

My furnace was over 20 years old so my solution was to buy a new one.  Solved my short cycling problem but I don't know if that was the new furnace or the install process that resolved my issue.

[Azúl]

Same issue. Nest short cycles on heat. Previous thermostat does not. C wire connected.

[georgejrpetre]

I just installed my Nest Learning Thermostat andit short cycles on A/C. Even if I set the mode to OFF the AC unit starts and the blower as well. With the T-stat set to OFF! 
Did you manage to get yours fixed last year? If so, how?

[Tbnilsen]

Was this ever resolved? I have same the short cycling issue. Seems that as room temperature approaches the Nest setpoint, the Nest starts short cycling the boiler. Is the Nest really trying to achieve that fine of a control of the heat? I’ve tried turning off the “smart” learning mode for overshoot, but the Nest (gen 3) still behaves the same way. Please help. 

[Tbnilsen]

Oh - and I do have the C wire connected. 

[EdwardT]

Hi Tbnilsen,

Thanks for reaching out. I'm sorry to hear that you're having an issue with your Nest Thermostat. I'd love to know more about this and I have a few questions:

• How is your Nest Thermostat wired?
• What is the power reading of your Nest Thermostat?
• How often does the thermostat short cycling?

Looking forward to your response.

Thanks,

Edward 

[Wellcraft19]

I'm new here, EdwardT.

Short cycling is often a result of a too tight hysteresis (as an example; thermostat shuts off heat at 71F and calls for heat again when temp has dropped to 70F) and/or that thermostat does not have timer built-in to prevent short cycling.

In older, maybe a beat leaky houses, it is often preferred to kick temp up to 73F and let it drop to 68F (numbers just as examples) in order to prevent short cycling and having the furnace actually run efficiently. In my case, I allow a bit of a temperature swing, and furnace generally only runs once in the morning and once in the evening, but for longer times. Still, far less than cycling on and off several times per hour.

That said, so here is my question; can one on the Nest thermostat adjust either the hysteresis or the timer, to prevent short cycling? And yes, it'll come at the expense of wider temperature swings, but short cycling the furnace is far worse.

[Tbnilsen]

Heat only, propane gas boiler, hot water radiant floor system.

TSTAT red and white wires

Common power wire

(total of 3 wires)

Vin reads 30VAC

During a demand for heat period, the Nest short cycles the boiler for over 4 hours in which most on-times (ie TSTAT relay closed) are less than 2 minutes. 

I suggest looking into the latest firmware release to see if somehow the Nest uses fast heat source control method (for example it uses the Electric Heat control method rather than a gas water boiler method). 

I’ll be happy to answer any more pertinent questions.

[Wellcraft19]

Here's my take: Your Nest should not control the boiler. The boiler should be controlled by the water temperature. The Nest should control the flow of energy (circulation pump or control a shunt valve/mixing valve). These 'on-off' thermostats works well on forced air systems where  'heat' response is pretty fast, but in your case, the room temperature has very little to do with the temperature of the water (which is what the boiler directly impacts).

[Tbnilsen]

I have new insight into the short cycling. Have your engineers look at using a 400mA load over a 50 foot wire (approximately 18awg) for what the Nest switches (ie as the furnace load). I did a bench test and with small loads the Nest does not short cycle. It keeps the “heat” on as it should. 

Nests have to deal with switching on 400mA zone valves in radiant boiler heating systems. It’s clear that the recent firmware reacts differently to switching larger such loads.

Please update the firmware asap. Winter is coming.

[EdwardT]

Hi folks,

@Wellcraft19, thanks for the input.  We don't have an option to adjust the temperature swing as of now and we don't have any news to share about this feature, we appreciate users who are keen on sharing their thoughts with us. We're always looking to improve — we'll take this as feedback. 

@Tbnilsen, We'd like to know more about this. Please fill out this form so we could investigate further.

Thanks,

Edward

[Tbnilsen]

Hi EdwardT,

thanks for your reply - I went ahead and filled in the form.

With respect, in your reply can you change “so we could investigate further” to something more assertive and hopeful like “and we will investigate further”? “Could” is especially worrisome.

I can assure you this short cycling problem is real and is not a User induced error. I just now did the same test as described in my filled in form with a second and even a third Nest gen 3 unit, all with same firmware and they all behave the same way as described (ie short cycle with high load/long cable, but work fine with smaller load/shorter cable). 

With the heating season racing upon us, I can’t allow the Nest to cycle my boiler in that fashion much longer. It’s too much of a strain on its various components, and I imagine especially the igniter. Thanks for your support. 

[EdwardT]

Hi Tbnilsen,

We got your form — thanks for filling it out. Our team will reach out to you via email to further assist you. Also, please be advised that this thread will be locked after 24 hours.

Thanks,

Edward

[Wellcraft19]

This is a typical result of primarily a too tight hysteresis ('swing band') in order to tightly keep to the set the temperature. But it is also detrimental to furnace longevity, it is detrimental to an AC compressor if present, and it is detrimental energy savings. The true savings are achieved by reducing total number of hours run (as most furnaces are single speed, and will cost the same per hour, regardless if it is 50F outside or -25F. Running longer and allowing for a bit of a swing, will help reduce total number of hours run.