Fan not automatically starting in heating mode

[Normalguy]

I recently moved into a new house which had the nest 2nd gen thermostat installed. In Cooling mode all works fine (Select the temperature and then the cooling system and fan start up no problem) but in heating mode I cannot get the fan to automatically start (Furnace kicks in and heats but I then have to switch the Fan on manually).I have another nest in the basement zone which looks to be wired the same way but that works (set the heat temp and both the furnace and fan kick in). Does anyone else have this problem and if so any solution?

[CoolingWizard]

The heating system has a specified start sequence. Let’s look at that and go from there.  Let’s verify the sequence is happening. 

1. The thermostat calls for heat.
2. The control board will run a self check to verify that the limit control and manual reset overtemperature control are closed and that the pressure switch is open. If so, the induced draft blower (inducer) begins a prepurge cycle.
3. The air proving negative pressure in the combustion chamber, the switch closes.
4. 15 seconds after the pressure switch closes, the gas valve opens and the spark is initiated for a 7 second trial for ignition.
5. Burners ignite and flame sensor proves all burners have lit.
6. The circulating air blower is energized after 20 seconds.
7. The control board enters a normal operation loop in which all safety controls are monitored continuously.
8. Once the Thermostat is satisfied and ends the call for Heat.
9. The gas valve is de-energized and closes, shutting down the burner flame.
10. The control board will de-energize the inducer after a five seconds, this is the post purge.
11. The circulating air blower is de-energized after 180 seconds.
• The integrated control board has a three ignition attempt system.
• After a total of three trials for ignition without sensing main burner flame, the system goes into a 100% lockout mode. The system will wait 1-hour. This can be interrupted by shutting off the power and then turning it back on.
• After one hour, the ignition control repeats the prepurge and ignition cycles for 3 tries and then goes into 100% lockout mode again.
• It continues this sequence of cycles and lockout each hour until ignition is successful or power is interrupted.
• During the lockout mode, neither the spark ignition control or gas valve will be energized until the system is reset by turning the thermostat to the “OFF” position or interrupting the electrical power to the unit for 3 seconds or longer.
• The induced draft blower and main burner will shut off when the thermostat is satisfied.
• The circulating air blower will start and run on the heating speed if the thermostat fan switch is in the “ON” position. The heating speed is lower than than the cooling speed.  

For the nest equipment configuration, we need to verify the configuration, on the Nest App, enter settings, Under Equipment, you should have the Heat Source set to GAS, and the Heat Type set as FORCED AIR. 

Ken , The AC Cooling Wizard 

[Normalguy]

Hi Ken, Thank you for the response. I have verified the equipment setup and its set to Oil and forced air which is correct for my system. In AC mode the system works fine (Cooler kicks in and the Fan) but for Heat the heater starts and heats up but the fan does not, I have to put it on manually. Please let me know if you have any suggestions on how to fix this. 

[CoolingWizard]

Normalguy, in a standard forced air heating system, the heating call signal from the thermostat arrives from the W terminal to the furnace control board.  The furnace control board is what should be turning on the blower. Now, there are some older systems that require the thermostat to activate the blower for both cooling and heating.  Thus, the thermostat would send a call on the G terminal along with the call for heat on W or the call for Cooling on Y.

Since the furnace control board activates the indoor blower fan with the AC cooling call, it should do the same with the call for heating.  With AC the blower starts almost immediately with the call for cooling.  With heating, there is a slight delay to allow the heat exchanger to come up to temperature so that cold air is not sent to the room on a heating call.  
I wan to give you a temporary test.  Turn the power off at the furnace and add a jumper wire between W and G. This will cause the blower to turn on immediately upon a call for heating.  Furthermore, the Heating call to the furnace control board, also should start the blower at lower RPM than for cooling.

Turn the furnace power back on, return the thermostat and make a call for heating. Let me know what happens.  

Ken, The AC Cooling Wizard 

[EdwardT]

Hi folks,

@CoolingWizard, thanks for the help!

@Normalguy, how's it going with your Nest Thermostat? Still need our help?

Thanks,

Edward

[Normalguy]

Thanks Ken I really appreciate your help here. I managed to get the system to work via the above steps you suggested (jumping the W and G wires). I also managed to get through to customer service and they advised me that there is an issue with my nest and I need to buy a new one to fix the issue  (my 2nd gen is out of warranty). I have ordered a new one so fingers crossed. Again thank you for your help. 

[CoolingWizard]

The concern I have is do we have a problem with the furnace control board or blower motor and not your thermostat. What’s important to note is when in heating mode the blower rpm is lower. And and cooling the RPM is always at maximum. I was hoping you could see or tell the difference in the speed of the fan when you were in heating.

[Normalguy]

Thanks Ken, well you might be right. Per the recommendation of the support line I bought a new thermostat, installed it and I still have the same issue. I found that in the pro install guide there is an option (under equipment, W1 wire) to set the fan to come on when heat is activated (apparently it is off by default), but I dont have access to that. I contacted customer support again and they are now saying that I need a nest pro installer to come out. At this point I dont know if its the settings in the thermostat or the HVAC control board. I am thinking about giving up on nest and installing a basic one that will probably work  

[CoolingWizard]

I am not sure a Nest Pro will be 100% suitable unless he is an HVAC technician as well.  We have proven the thermostat wire conductors  are functional  and signals reach the controller.  What we need to do is evaluate the Furnace Control Board. However, you have clearly stated the conventional thermostat does indeed start the blower when heat call is initiated.  This leave the Nest Thermostat or it configuration is not correct.  Since you have a nest thermostat in the basement,  and as you stated, wired the same, just swap them and see if the problem moves.  Just take the one upstairs to the downstairs and vice versa. If the problem moves downstairs and the upstairs works correctly, this thermostat is the problem. If the problem remains upstairs, the problem is in the Furnace control board.  

I was looking back over your messages and I missed that you said you have an oil fired boiler for heating. Does your system have a hydronic heat exchanger in the system? That is, the boiler heats water, the hot water is sent to the furnace blower to exchange with the cool air.?

[Normalguy]

Thanks for the suggestion. I tried swapping the downstairs for the upstairs one and no luck im afraid. 

Yes my system an Oil furnace with a hydronic heat exchanger. I found this in the next pro handbook (Page 22) which seams to reference a fan setting for the W1 wire under the equipment settings. Apparently the fan is set to "dont activate" by default. I dont have this option so I assume this is only available to a Nest pro installer? http://support-assets.nest.com/images/pro-faq/Nest-Pro-Installer-Guide.pdf  

[CoolingWizard]

This is basically where the more complex systems require an experienced HVAC technician to assist in the installation and configuration and it seems that the person who installed that nest thermostat did not do that. I was simply trying to help determine where the problem lies when I advise you to put that Jumper between W and G. Most modern maybe within five or 10 years furnace control systems now have smart control boards in them because they use multi speed fans. They’re typically set up so that they spin at a lower rate RPM for heating and a max rpm for cooling. The thermostat is difficult to control something like that. What I need to help better understand your system is a picture of the manufacture label on the air handler furnace unit. Is that possible to get? 

[Normalguy]

Ok thanks. I don't have permission to upload photos but the make is "Carrier" and it looks like the model number is FB4BNF036 if thats of use?

[CoolingWizard]

Based on the information you gave me for the model number I was able to look up the manual, and that particular air handler does not have a heating delay designed into it. Therefore when the thermostat was installed it should’ve been installed as a nest pro installation and therefore the proper setting set to cause the thermostat to turn on the fan with the heating call. Essentially we did this manually when we jumper the W and the G wire. Now we just need to go into the software and make the nest normally do that by itself and all will be good.

Ken, The AC Cooling Wizard

[CoolingWizard]

I have found the key to uploading a picture, as you must upload the photo before you type any text in the text box. So what I do is I tapped a little camera choose the photo then I go ahead and add the text afterward and that seems to work

[Normalguy]

Thanks Ken. I am able to upload them now but it sounds like you have the information. Let me know if you still want them. Great news on the trouble shooting. Is this something that I can do or must this be done by a nest pro installer?

[CoolingWizard · Accepted solution]

Normalguy, 

You should be able to do this.  
1. Tap the thermostat to get to the Menu

2. rotate ring until you reach Equipment; you see a picture of backplate with wires

3. Press continue 

4. you will see equipment settings, go down to Pro Setup and select 

5. you will see a warning about doing something wrong could be bad click continue

you’ll see a picture of the back plate with yellow and green highlighted wedges, rotate to the W

you will see how the current system is set up for example it may say heat gas forced air don’t use fan

6. Press the ring and it will allow you to edit the W. On the bottom it will say fan don’t activate, highlight that, Press the ring, and then rotate and change it from don’t activate till it says activate. Tap continue. Then tap DONE. 

Ken, The AC Cooling Wizard

[Normalguy]

Ken, I think we are getting close but I dont see the option to set the fan when I have the heating system set to Oil. I do however have that option when I set it to gas. Should I set it to gas and give it a go or will that mess up my system?

[Normalguy]

This is the option when source is set to gas

[CoolingWizard]

This is also where you change that don’t active to active scroll down to don’t active, press and click, then rotate to active, then click done

[Normalguy]

Thanks Ken. My system is an oil system though and when I have that selected as the equipment type, then I dont have the option to change the fan setting. If I switch it to a gas system (which is issnt) then I get the option to change the fan. Should I change my equipment to gas and try the fan option or will that cause damage? Again I really appreciate your help here 

[CoolingWizard]

It will not hurt the system to set it to gas and set the fan to active.  

Ken, The AC Cooling Wizard

[Normalguy]

Ken, it worked! Thank you so much for all your help here, I really appreciate it. Take care. 

[Jeff]

Hey Normalguy,

It looks like you were able to get this sorted out. I'm happy to see things are working. Before I mark this as resolved for you, is there anything else you might need? If so, just let us know.

Thanks,

Jeff

[Jeff]

Hi all,

As we got our resolution here, I'm going to mark this one as resolved in the next 24 hours. Thanks to all who helped and contributed. If anyone has any other needs, please feel free to let me know before the lock.

Thanks,
Jeff

[EmersonB]

Hello everyone,

@Normalguy just one quick final check in here since activity has slowed down. We'll be locking the thread in the next 24 hours, but if you still need help, I would be happy to keep it open. If there's more we can do, just let me know.

I appreciate the help, @Jeff and @CoolingWizard.

Regards,
Emerson