Wednesday, November 14, 2018

Thermostat Replacement Errors and Attempts and Troubleshooting

I'm not normally into self-humiliation, but for the good of mankind, I am willing to expose my thoughtlessness in this case.

It all began when my mother-in-law told my wife that her thermostat was too complicated to understand. I did some quick research for an ordinary, simple thermostat and ended up buying the Honeywell RTH5100B. It is a non-programmable unit, where you simply press the up button when you want the room warmer and the down button to make the room colder. During setup, you tell the thermostat whether or not you want it change automatically from heat to cool. I did.

Error 1. I neglected to turn the system off at the circuit breaker (or the switch on the furnace unit) before I started unscrewing the old thermostat.
Consequence of Error 1. Two of the thermostat wired touched together and made a tiny spark. Unbeknownst to me, a fuse inside the forced air unit was fried out of its mind, giving its life as a sacrifice to protect the valuable electronics in the furnace, and to save the bacon of the idiot  doing the repair.

Error 2. In this old house, I assumed without checking, that the gas furnace was just a simple gas furnace. I didn't know what that extra brown wire was for, connected to the W2 terminal.
Consequence of Error 2. Of course, nothing worked with the fuse blown. I ended up calling Honeywell. The representative said that the brown wire on W2 meant that the furnace had two-stage heat and that the RTH5100B would not support that. So I had to buy a new thermostat, the RTH6360 series, the purchased model being RTH6306001002. At some point in the process, I learned about the fuse, maybe from the Honeywell rep or from the documentation. Home Depot helped here by supplying replacement fuses ( I bought several).

Error 3. I installed the new thermostat (turning off the power first) and wired it up as indicated in the manual. It was a warm day, so I turned on the  AC and lo and behold, the system started up and ran fine. So I congratulated myself, packed up my tools and took off--without checking the heat function.
Consequence of Error 3. I got a call the next day with the news that the heat did not come on. I drove on over and checked the wiring, the circuit breaker panel, the furnace switch, and the programming. I couldn't get it work.

Error 4. I left the installation manual at home, so I didn't have the codes to double check the system setup.
Consequences of Error 4. I was limited in what I could check. I tried to use my cell phone to get on the Web and find the manual, but it was hopeless. So I basically wasted the trip.

So now I made list of things to check not make assumptions about:
1. Check to see that the connections of the wires are tight and that they are all metal to wire, with no wire insulation preventing a connection. (Make sure the connecting screw didn't accidentally push down on the insulation instead of the wire itself.)
2. Check to see whether the furnace is high efficiency or standard. High efficiency has plastic pipe vents (white PVC or black ABS), and standard has metal vents. I recall now that the thermostat selection in setup required a choice between the two types. Its default is for high efficiency. If the furnace is standard efficiency, change that setting in setup.
3. Check the connection between R1 and RC (sometimes labeled RH and RC). The RTH6360 does not use jumpers between R1 and RC because there is an internal connection made by sliding a small switch inside the thermostat. Check to see if the switch is in the right position for a one R wire (position is UP) and that there is continuity between the two. (I put a short piece of wire in each of the sockets for R and RC to check.)

1. All connections proper.
2. Furnace is standard efficiency, so I set the thermostat to match that.
3. R1 and RC are properly connected to each other and the switch is in the right position.

So I called Honeywell and spoke to a technical assistant. We went through the configuration settings. Then he had me connect the control wires R1 and W together, bypassing the thermostat and sending power directly to the furnace logic board. We waited  ten minutes. (By the way, the furnace interlock switch worked, and thermostat clicked, the furnace clicked and I had turned the power back on. The green "heartbeat" light blinked as normal. But no furnace.)

So now it's time for some YouTube research.
It seems that the inducer fan motor might be the problem. Will have to check it out.

Error 5. I didn't check the extremely unlikely. When I got back to the furnace, I checked and rechecked everything. I read the panel notes and discovered a way to run a test cycle by shorting between a TEST post and one other wire. The inducer fan started, the igniter glowed, the fan came on. Seemed as if everything worked. Frustrated, I put the old thermostat back on, since I thought that the system was working before. No luck. I just couldn't figure out what the problem could be. So humiliated for the third time, I left. On the way home, I thought, "Maybe I should have checked for continuity of the W wire." But how likely is it that a thermostat wire would be broken? And the W wire, at that? And none of the others? Yeah, right." You can see where this is going.

Weary of failure and humiliation, I called a professional furnace repair company.  George went over the things I had gone over and then checked for the continuity of the W wire. It was open. George didn't have any thermostat wire, so he called Albert, who came over and ran the new wire. He had to climb into the attic to achieve this, so I consoled myself with the thought that, even if I had figured out the problem, I couldn't do the attic work (not as young and limber as I used to be), so I would have had to call a pro anyway.

So the furnace works now. And now I know that the unlikely does happen. Should I therefore start buying lottery tickets?

P.S. The thermostat works very well.

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