Before going into crawl, I went to a very fancy T-stat (couldn’t tell you the brand but it was a touch screen) and quite easily upped the thermostat from 69 degrees to 76 degrees to fire up the furnace. It was a Lennox high efficiency and the burn chamber was fully enclosed and not visible (I usually take a pic of the flame and remark on it’s color). No pic to take. so it’s time to check the filter so before I open the filter access, I flipped the Service switch off and check out the filter - it’s clean, I put it back and turned the Service switch back on and wait for it to cycle. It doesn’t. First I checked the panel and the breaker is fine, then I checked the service switch and sure enough power is being fed to the furnace control. so I asked the Realtor to get hold of the seller and let them know. Well the seller called out a service tech and $486 later it’s purring like a kitten. The receipt said “t stat was faulty needs to be replaced”, so that’s what he did. Should I have done something different? Sometimes stuff breaks under testing. I mean, this is a 1st one that I’ve had a T stat blow because I turned off - then on - a furnace at the Service Switch. But then again I’ve never seen a thermostat like this one before -
AFIK disengaging the service disconnect shouldn’t kill the t-stat. Who sprung for the replacement?
WAG… It’s a computer. Would you ever ‘kill power’ to your computer without properly shutting it down first? With newer and newer technology, you guys need to be better aware of what you are dealing with, and handling it appropriately.
At this point, the seller paid the tech by check. I haven’t heard if he is going to come back on me for it. The seller’s very vocal Realtor told the buyer’s Realtor that “the inspector shut it down wrong” and that I even “told the seller that [I] know nothing about H.E. dual phase furnaces.” I did talk with the seller on the phone to try to help figure out what went wrong - I never claimed to “no nothing” about his furnace - I told him that I did a check of his furnace like every other furnace I’ve checked and that the furnace failed to re-set after I turned the service switch back on. I also told the seller, and he agreed, that if the service switch should not be thrown, it should have been removed when the new furnace was installed back in 2016. As I mentioned, I did see a copy of the repair receipt and it made no mention of an “improper shut down” - it gave no reason at all for the thermostat failure - it just said it failed and was replaced.
This is what I put in my report: “Unit was tested using normal operating controls. It operated at time of inspection. The Service Disconnect Switch (located directly above and in line with the furnace power supply) was turned off to inspect the filter, as is the standard procedure to prevent the fan from activating when the filter is being removed. The interruption of power de-activated the thermostat / control module located in the stairway hall. It did not re-activate when the Service Disconnect Switch was turned back on. Have a qualified service technician resolve the issue of the thermostat not resetting when the power is interrupted.”
IMHO the thermostat should have a capacitor / battery back-up to deal with power interruptions (like a power outage or a person throwing the service switch) - just like my computer at home does - Thanks for your input.
Just how would you handle it appropriately? How would you inspect the filter? Would you go online and find a user manual and download it and figure out how to go through the program screens to see IF there was some special procedure to inspect the filter - unlike every furnace that I’ve ever seen? IMO it is foolish to pull a filter unless the power is cut - the fan coming on has the potential to 1) suck a dirty / sagging filter into the fan or 2) suck any loose dirt in the return into the heat exchangers.
thanks for your input - I really want to know what your “better aware” mind would have decided to do.
I would like to know also
Shut the HVAC down utilizing the Thermostat,
Turn the Thermostat OFF,
Proceed to HVAC and turn OFF Servicemans switch,
Proceed with inspection.
Reverse steps to energize system.
This was your mistake, IMO.
Yes. All the time. What happens in a power loss event? I have 4 relatively expensive thermostats for my boiler zones and I have thrown the switch plenty of times with no issue ever.
While I agree that he could have taken different steps and followed a different procedure I still see no flaw in operating existing means of disconnect.
Everybodies entitled to their own opinion. You now have mine. Have a good weekend!
I have not been doing step 2. I am adding it to my procedure now!
@ jjonas The reason you don’t kill power to a computer is to prevent data loss. The hardware is not susceptible to sudden power loss. Any thermostat that can’t handle sudden power loss is a POS and I’m hard-pressed to believe it was designed with that vulnerability.
@ snadeau I would be contacting the manufacturer’s tech support department to find out from them if their thermostat is designed in a manner that leaves it vulnerable to sudden power loss and if there is a specific shutdown procedure that is supposed to be taken before powering down the furnace/air handler (I highly doubt there is). IMO someone should have checked (tech/homeowner) the warranty status of the thermostat. I would need to see the documentation that powering down the furnace with the service disconnect is “improper procedure” before I tolerated any abuse or forked over money for it).
Who can anticipate everything. %^&* happens.
The receipt said “t stat was faulty needs to be replaced”,
Everyone assumes the T-stat really needed to be replaced.
Could be an example on an overzealous tech, looking to install parts that aren’t needed.
I’m sure most of us have seen this happen to many clients.
Why even remove the filter in the first place? Just to check if it’s dirty? You usually can open the door or cover to make sure there is a filter and to note type and size, but Regardless if it’s dirty or new I always put in a note saying “Changing filter on a regular monthly basis is always advised”. Unless they have an electronic type filter or another type other then disposable don’t mess with them. Note if there is one, size and type and be done with it.
It could have been as simple as the batteries in the t’stat for backup power were dead. When you killed the power at the disconnect, the t’stat reverted to the factory default heat setting (usually 55°). I don’t know if you checked the t’stat setting after you restored power at the disconnect; or whether you just assumed that the t’stat had retained the 76° heat setting.
[David Williams, NACHI 18092410](https://forum.nachi.org/u/dwilliams49) InterNACHI®️ CPI April 15
It could have been as simple as the batteries in the t’stat for backup power were dead. When you killed the power at the disconnect, the t’stat reverted to the factory default heat setting (usually 65°). I don’t know if you checked the t’stat setting after you restored power at the disconnect; or whether you just assumed that the t’stat had retained the 76° heat setting.
The stat had no replaceable batteries, and was just a blank screen after the power cut. It was a sealed case, powered from the four wires in the thermostat low voltage bundle.
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It could have blown the 3-amp automotive-type fuse at the fan-control board, if there was a loose wire there. Just another possible explanation. And any HVAC tech always carries a couple in his pocket. I just can’t go with re-powering at the the disconnect causing the t’stat to fail. Could have even been a failing low-voltage transformer. They will cause the low-voltage fuse to blow sometimes. This is another cheap item an HVAC tech will have on his truck. / If there’s no automotive-type fuse present (for future reference) look to see with the power turned off, of course, if there is a little reset switch or button on the side of the LV transformer.
After the access panel to the filter was slid back, the filter was recessed and held in place with a spring “bar”. The only way to note the size was to remove it in this case. But in every case on my inspections, I show with photos where the filter access is and how the filter should “look” when installed properly. If possible I show the client in person how and why to replace the filter. In this case, my client was a single mom with 3 knee-high kids and I want to make sure she knows how and why to change it. I also note whether the filter is clean or dirty, as that in itself is an indication of the condition.
Steve, You did not do anything wrong and I would not change your procedure except maybe turning the service switch off first, then raising the thermostat, then switch back on. Watching it start up can reveal a lot more than getting to it while running for a while. Not a HVAC tech, but have some of a electronic engineering background. Chuck and David Williams have the correct responses imo. thermostats should be designed with multiple power shutoffs at the prototype testing stage.