: X10 interference from furnace thermostat
We recently had a new furnace installed along with a new thermostat. This is the Carrier Infinity model -- the thermostat is like a computer with a zillion options and status information. It only uses the same four wires that were there before so it must be exchanging X10-like signals with the furnace. Anyway, an X10 light switch that is only a few feet from the thermostat keeps getting turned on! No other modules are affected so it must have something to do with the proximity rather than getting noise onto the electrical lines.
Has anyone else had such a problem and any suggestion on how to solve it?
2006-03-05, 10:45 AM
Ferrite chokes. You might be able to get smaller ones you can install in the thermostat.
2006-03-05, 01:46 PM
The ferrite chokes are a good suggestion.
Before you do that, you might want to experiment.
First, try changing the house code/unit code on the flakey module. I don't think this will work, but it's easy to rule out.
Secondly, trade the flakey module with another one. It might be that it is particularly sensitive.
It's kinda weird that the interferance only turns on the module. Usually X-10 interferance stops a module from working at all.
The x-10 protocol is rather arcane. It's hard to believe that the thermostat is sending the exact combination of frequencies in the right order to turn on a sepcific house-code and unit code.
The link below is to a powerpoint lesson on how the x-10 protocol works.
Given these complexities, it's hard to believe the thermostat is sending the correct combination 120Kz for 1 milisecond, spaced by appropriate blanks, then complemented, then exactly repeated.
So I think something else is going on.
Try the suggestions, and let us know. We'll keep trying to help.
It's a bit of a long shot, but is there any chance you have a neighbor serviced by the same distribution transformer that has some X-10 equipment as well?
(see where I'm going with this?)
Thanks for the responses.
I did try changing the house code and also changing the module. Problem still exists. I doubt if it is a neighbour problem given the timing -- the problem started nearly exactly when the new thermostat was installed. Not exactly though, which is a mystery. It did not happen the first night, only started the next day. So there is a slim possibility that it is something else!
Yes, I doubt that the exact sequence of bits is being sent. And of course, the thermostat does not send data via the house wiring -- it has its own pair of "data" wires to the furnace and is powered on another pair of wires carrying 24V from the furnace . So that is even more strange. What I suspect is that there is some sort of RF interference that is just so strong in the vicinity of the thermostat that it is overpowering the X-10 module somehow.
As for the ferrrite chokes -- can you be more explicit about what they are and how/where to install them?
do you know if you have an active phase coupler?
I used a Leviton model (I think an HCCA10....something or other) for a while, it would create extraneous stuff with my automation controller and give me very random and un-appreaciated behaviour - devices would initiate scenes without being called on to do so, lights would go on - then off again.
the best basic active type couplerrepeater I've seen/used is the ACT CR230, it's a bit spendy, but it will always serve it's purpose very well.
2006-03-07, 11:33 AM
The link below shows an example of a ferrite core.
They're cheap and it's certainly worth a try.
I think your assessment on it being the module swamped by R.F. is the most likely cause given that you changed codes and modules. The only thing about that is to suggest changing the module to a different make. If it is x-10 brand, try something from leviton or smartlinc.
Keep troubleshooting, and you'll get it.
It's likely *not* your thermostat that's causing this problem - as far as I know the thermostat connections are DC and probably connected to your furnance via relays -- and very doubtful if they are directly connected to your AC powerline. (Does the Carrier Infinity have a wireless option - could these messages be getting on your powerline via an X10 transceiver?) It's likely the motor noise from your new furnace washing into your AC signals.
You might try an INSTEON switch. The protocol is far more robust and it can work in a hybrid X10/INSTEON environment.
Ok -- I guess the best bet is to try another make. I am not familiar with any of them -- I have always bought "Plug 'n Power" at Radio Shack and now The Source. I just checked for Insteon and found Aartech Canada. Is that a good source? I see they have a relay wall switch (no dimmer so it can control fluorescent's -- good because I want to change the bulbs in that fixture to CFBs). But it is $43.95!!! Is it an ok price?
Thanks again for all the suggestions!
2006-03-09, 05:23 PM
The plug and power were/are re-branded x-10 devices. They're likely the lowest quality PLC devices available.
The insteon non-dimmer that you are looking at is likely a good bet. Just double check that it is x-10 compatible. Most, but not all, insteon switches are.
Keep us poted on the outcome.
The switch is a Smarthome ToggleLinc Relay -- and it definitely says it is X-10 compatible.
2006-03-09, 10:15 PM
The price isn't bad. It's around $40US at smarthome, then there'd be shipping, so your Canadian source sounds reasonable.
2006-03-14, 02:03 PM
Unless it it uses some high-tech signalling protocol, typical thermostats are 24V AC
Received the switch and installed it yesterday. Quite a bit more complex than the old Radio Shack variety! It needs to be connected to neutral (which in my case is a big bundle already containing four wires - it was hard to get at!) and also needs to know which is hot and which is load. The primary address is not set mechanically -- you press a reset button then send a signal from any X10 controller -- it picks up the address on the first signal after reset. This did not seem to work after many attempts so I started to send an email to their tech address. Just before sending it I tried one more thing: you can do a "factory reset" and it then defaults to A1. I tried doing that and resetting my controller to house code A and that worked! So I will leave the house code at A. Otherwise, after 24 hours it appears to be working ok. Keeping my fingers crossed.
Classicsat -- yes, the thermostat uses 24 volts for power. But it also has two "data" wires which carry signalling information between the thermostat and the furnace. It is not just an "on" and "off" like most thermostats. There are dozens of parameters that can be set at the thermostat and much status info that can be read at the thermostat. I do not think that signalling info is getting into the X10 units, but I suspect that the themostat itself generates some RF interference which was screwing up the X10 switch near it in some way. The new switch seems immune to it.
2006-03-16, 05:15 PM
Thanks for the update. It sounds like you may have solved it as far as the interference is concerned.
I've used the smartlinc switches and normally they take an address easily. As you know, you push the little switch in and hold it until the LED's cycle, then send a house code/unit code ON command and they take that address.
What are you using to send the code? It shouldn't really matter, but maybe it does.
Keep us posted...
Well, it is partly solved! At certain times (I think it is when the furnace is running on high) there is a lot of "activity" on the line (shown by the little status led blinking merrily away) and the switch won't generally accept X10 commands then. (I can get it to turn on with 5 - 10 presses of the controller switch.) At other times it works fine.
I now suspect that perhaps the furnace signalling wires and the power lines to this particular switch are running together for a ways and perhaps the furnace and thermostat are communicating with X10-like signals. Some of that activitly may be leaking into the power lines close to the switch. I can't really think of any other explanation.
It's better than before since the light does not seem to ever come on by itself. But I have to make sure it turns off when it should -- nothing worse than an interior light on all night. Sort of says "Hey -- I'm not home!!"
rwalker -- I was using an old Radio Shack mini controller. I suspect I was trying to set it while it was getting a lot of interference. However, I'm happy using the A1 default now, so I won't experiment with that anymore.
2006-03-21, 12:57 PM
The x-10 protocol is arcane in it's bit pattern but simple as heck in it's basic transport. If an x-10 receiver sees 1 milisecond of 120Khz during the zero crossing of the AC sine wave, then it thinks X-10 is coming in. It then try's to decode it.
So, given that your device is lighting up, then the furnace is imposing 120Khz on the line. It's normally not being decoded as a valid signal, because it's not organized, but the reciever is trying.
Your suggestion that the lines may be running close together is a good bet. Or the furnace controls or motor are noisy in the 120Khz range.
A filter in the correct place may solve the problem. See the post about multiple x-10 devices not working with compact flourescents.
Keep us posted...
2006-03-27, 02:44 AM
Another thing you could try is replacing the thermostat wiring with shielded wire. This is pretty much standard for low level signal cable these days. You will need at least 5 conductors plus a shield. You can probably pick it up at Home Depot or a place that sells furnaces and thermostats. Make sure it is rated for 24 volt thermostat use. Do not use computer networking or similar cable. Connect the shield conductor to a good ground at one end only, preferably at the furnace.
You should also check the electrical wiring to the furnace to make sure it is in good condition. Make sure the furnace is on its own circuit breaker. (This is required in most places.) Finally, you could try switching the furnace circuit to a breaker on a different phase. This might reduce interference through the electrical wiring.
Thanks for all the suggestions!! I don't think I am up to re-fishing the wires -- it is quite a distance from the thermostat to the furnace. I do think this would be a good idea, but I would have to pay someone to do it. When I got the new furnace they warned me that they might have to place the new thermostat in a new location (closer to the furnace) if the old wiring was not suitable. If I had known about this problem, I would have told them to just do that anyway!!!
Currently everything is more or less working. The "on" and "off" times I have programmed for this fixture seems to be at times when the furnace is not having to run. In particular, the "off" times are just into my "sleep" period when the temperature drops so the furnace should never be on for the first few hours. I have also added another timer (an old one I happened to have lying around) and programmed two more "off" times after midnight -- just in case! So far, so good! But I do know that there are times when there is still interference. so it is not ideal. And who knows how it will be on a really cold day next winter when the furnace is having to run a lot. I guess I'll worry about that when the time comes!!
btw, I replaced the lights with mini-fluorescents and that is working too!
Here is the fix you need:
Works like a champ. The filter needs to be installed in the furnace.
I had the same problem, random light turn-on's with a carrier 58MVB furnace.
I believe it's Carrier's problem since there doesn't appear to be any RFI fitering on the furnace. It's likely caused by power line pollution from the variable speed drive of the fan.
Fix works, guaranteed.