Hello,

I've had a perfectly operating Gas Water Heater and Gas Furnace system until about 4 weeks ago.

For whatever reason, my Gas Furnace stopped and it sort of starts up on its own. It stops whenever we're not in the house and overnight so we wake up freezing with house temperatures around 50 degrees F. I tried shutting off power and restarting, cleaning the furnace, changing the thermostat settings and nothing worked.

Then I noticed that it wasn't until the Water heater kicks in that the furnace started up again. I have proven this by trying several things. I would turn up the Water Heater setting to a high enough setting to force the water heater to start and then immediate the furnace would start up. I can also turn the hot water and let it run for about 5 minutes and that forces the hot water heater to kick in at which time the furnace would then kick in.

I can't figure out why that is. The only connection between the Gas Water Heater and the Gas furnace is a small cylinder that doesn't really have much of anything written on it. I'm not sure why the two are connected in the first place either and not sure if that device is really needed. I'm suspecting that gadget is the problem but I'm out of my league on this.

Any help/clues are much appreciated.

Casey

Yes, strange. Too bad we don't have the likes of a Speedball1 or tkrussel in this area. Some others and I do what we can, but not sure we always come up with a good answer.

How is that cylinder connected, wires, piping? If it is wires, I would try disconecting one at the furnace and see if the furnace will work. At least you will be warm tonight while waiting to find out more.

There are some others here that know as much or more than I do. See if they know what the cylinder is.

Hello,

I've had a perfectly operating Gas Water Heater and Gas Furnace system until about 4 weeks ago.

For whatever reason, my Gas Furnace stopped and it sort of starts up on its own. It stops whenever we're not in the house and overnight so we wake up freezing with house temperatures around 50 degrees F. I tried shutting off power and restarting, cleaning the furnace, changing the thermostat settings and nothing worked.

Then I noticed that it wasn't until the Water heater kicks in that the furnace started up again. I have proven this by trying several things. I would turn up the Water Heater setting to a high enough setting to force the water heater to start and then immediate the furnace would start up. I can also turn the hot water and let it run for about 5 minutes and that forces the hot water heater to kick in at which time the furnace would then kick in.

I can't figure out why that is. The only connection between the Gas Water Heater and the Gas furnace is a small cylinder that doesn't really have much of anything written on it. I'm not sure why the two are connected in the first place either and not sure if that device is really needed. I'm suspecting that gadget is the problem but I'm out of my league on this.

Any help/clues are much appreciated.

Casey
I think you don't have a hotwater heater but only a hot water tank... your gas furnace (or boiler?)... the boiler is use for 2 purpose... 1 for comfort heating... 2 for domestic water heating... the domestic water is heated from the heat of the boiler( through a heatexchance)... DO YOU have a boiler/ an actual hotwater heater??

Casey may be on to something. I was assuming a conventional hot water tank and forced air furnace. Does the hot water tank actually have it own gas supply and burner? Is the furnace hot water or forced air?

Ok I just got my boiler replaced, but the tech that came in said I need a chimney liner. I don't know what the hell that means. But the strange thing is he is saying that my water heater needs to be change because it to big and I should have a low boy (40gallon) tank and that if they put the liner it wouldn't fit. I don't understand? I live ina single family home about 800 to 1000sqft. Please help me understand.

Ok i just got my boiler replaced, but the tech that came in said i need a chimney liner. I dont know what the hell that means. But the strange thing is he is saying that my water heater needs to be change because it to big and i should have a low boy (40gallon) tank and that if they put the liner it wouldnt fit. I dont understand? I live ina single family home about 800 to 1000sqft. Please help me understand.


Once upon a time, chimneys had the same brick or stone inside as outside. Later, clay tile liners were added. For a long time now, chimneys have had metal liners, mostly double wall. Unfortunately, combustion produces water and acids, and can eat holes in the liner, more quick if there is a condensation problem. So your liner may have holes in it allowing carbon monoxide and other nasty stuff to leak into your house. So, yes it is quite likely you do need to have the liner replaced.

Now I don't quite understand the problem with the water heater. If it is gas, it must be vented, and the vent needs to go up. Some mostly horizontal, but rising is OK. If it worked fine with the old boiler, it was the responsibility of whoever installed the new boiler to make it work. Maybe you need to invite the local building inspector for a visit. He may place a high priority on the bad liner.

Ok yes I understood that part about the chimney liner, but does the liner, and water heat connect along with the boiler? Is that why I need a new one. According to the tech, if he place a liner then it would become a fire hazard because it would be touch the roof or the top of something. I will get more detail when he calls back but does this sound familiar to you

The boiler has a heat exchanger with water on one side and the gas combustion on the other. The burned gas and air go out and up the chimney. The water heater has the burner at the bottom, and one or more tubes up the middle for the burned gas to go up through transferring the heat to the water. In both cases, there is a layer of metal separating the burning gas from the water. The boiler and water heater will both feed off branches of the gas and water and may tie together to go up through the chimney. There are fittings made to protect the roof from the heat of the liner.

Ok thank you. He explained to me that the water heater height is to big for the liner and it does not have proper ventilation.

Scrap the existing unit and go for an indirect water heater that will utilize your boiler to heat your domestic hot water. Hopefully you purchased a high efficiency unit, you will save energy versus a stand alone model.

Ok. It just that the one I have is only 2 years old. LOL and also I can't really afford it.

But I have no other option at this time. But thank you . You've been extremely helpful. Besides its good points on the house since I'm trying to sell it.

My post explaining that the hot water heater may have too high of a firing rate for the size of the vent seems to have gotten lost. If so, it might be possible to derate the current water heater to fit the existing vent. It would just be slower to recover from using water. It might be even more efficient.

Casey may be on to something. I was assuming a conventional hot water tank and forced air furnace. Does the hot water tank actually have it own gas supply and burner? Is the furnace hot water or forced air? I have what looks like a separate Hot Water Tank and a separate Forced Air Furnace. The hot water heater has a pilot light underneath it that I went out once (a long time ago) and I had to manually follow the instructions posted on it to light it. When it lit up I did see a flame under the tank. The furnace I believe has its own flame as well. Whenever it went on I do see the flames through the vent holes. The two are separate with the exception of this one cable that I mentioned. I think I'll take some pictures and post if I can figure out how to do that. It might make sense to see a picture.

Casey

P.S. I added pictures of the Water Tank and Furnace and a close-up of the cylinderical object I mentioned in my earlier post.

Your pictures show exactly what you described in your original post. Some of the forums here, we have experienced, trained people that have seen almost everything and can give excellent answers. We are struggling in heating and cooling. I am a home owner that has solved a few of my own problems and have some industrial trouble shooting experience too. I manage to knock down some easy ones here and there. I have never seen a gas water heater wired to a gas forced air furnace. Nobody else seems to have much of an answer either.

Furnaces and hot water heaters have worked for a long time without whatever that is. It looks to me like some kind of a pressure switch. It must have gone bad if things worked before, but not now. I have asked our top electrician and plumber to look at your question. If neither of them know what it is, it may be time to call a local professional. If you don't know who installed them, look for a decal or check the phone book for a dealer. You might check the websites for the heater and furnace.

Find out what it is and make sure local regulations don't require it before ripping it out and pitching it.

Your pictures show exactly what you described in your original post. Some of the forums here, we have experienced, trained people that have seen almost everything and can give excellent answers. We are struggling in heating and cooling. I am a home owner that has solved a few of my own problems and have some industrial trouble shooting experience too. I manage to knock down some easy ones here and there. I have never seen a gas water heater wired to a gas forced air furnace. Nobody else seems to have much of an answer either.
I thought it was strange as well that these too are "connected".


Furnaces and hot water heaters have worked for a long time without whatever that is. It looks to me like some kind of a pressure switch. It must have gone bad if things worked before, but not now. I have asked our top electrician and plumber to look at your question. If neither of them know what it is, it may be time to call a local professional.
Thank you for taking the time to pass this around. I really appreciate it. I think I'll run down the ACE HW store and see any of the water heaters come with that part. Like you said it could be something local to my area.


If you don't know who installed them, look for a decal or check the phone book for a dealer. You might check the websites for the heater and furnace.

Find out what it is and make sure local regulations don't require it before ripping it out and pitching it.
I bought the house as a new construction so we're the first to live in. I think the local contractor that built the house is still in business and I may call them to find out more. In the meantime, I went down and took a couple of more close-up pictures of that cylindrical object again. Maybe someone will recognize it.

Casey

What is that black cord draped over the drain valve? Power to an ignitor? I did a search on the GFP4563 I could read on the yellow label and found nothing. You might try a search on the P/N on the blue label, I couldn't read it.

What is that black cord draped over the drain valve? Power to an ignitor?
It looks like it is a CO detector mechanism. I've attached a picture from each end of the cable. Not sure how it works but the top part near the chimney has these two tin can boxes with what I think is a CO detectors. One winter I lost complete heating (both water and furnace) and I troubleshot it myself and determined that it was the tin can box after researching the part number on the net. Back then I had to open the tin can box and inside I had to "reset" by clicking a sensor with a pen or something... kinda like one of those wall outlets that has a red/black reset switches. Anyway, as soon as I clicked it the heat (water/furnace) came right back on and I haven't had that problem since. So once it goes off it shuts off gas completely (inluding the pilot light).


I did a search on the GFP4563 I could read on the yellow label and found nothing. You might try a search on the P/N on the blue label, I couldn't read it.
I looked up every clue I could on the yellow label but didn't bother with the blue one. The part reads:

FIELD CONTROLS
P/N 46284200

I did a quick search on the net and it turns out your original hunch was correct. It is a Gas Pressure Switch that controls CK-20FV, CK-81, CK-91F, CK-92F, CK-HWK. No clue what those parts are but I've got some homework to do and I hope to find out more.

Ok it looks like this thing is a Gas Pressure control unit. So based on that and seeing how it is connected, it looks like if the pressure changes (goes up or down, dunno) then somehow the electrical circuit that leads to the furnace is disengaged.

So this could explain why when the water heater starts the furnace starts as well. It would seem to indicate that the start of the gas furnace somehow reduces the overall pressure in the gas line enough to re-engage the electrical switch that controls the furnace.

So the next question is "why?". Could this be happening because the gas pressure is too high or is it because the Gas Pressure control unit is bad? Seeing how I live in Massachusetts and recently there was a major problem in a near by town (Lexington) where the gas company somehow over pressurized the gas lines and caused one of the homes to blow up I think it is best to stay on the safe side and call the gas company to have them check the pressure.

I want to thank you all for the help. The discussion here definitely helped me understand what is happening at least (unless I'm way off again).

Casey

The furnace seems to be dependent on the gas valve on the water heater, via the pressure switch. I have never seen this done before, but being an electrician, and not in MA, I cannot say why. Have wired many a heating and water heating systems, but never saw this pressure switch system.

I suggest you first contact the installer, esp if this is a new home and maybe under warranty, before any changes are done to either void the warranty or void any local codes that require this type of control system.

The installer can fix what ever needs to be repaired, and more importantly, train you on the system oerations,exactly how the system should work, and what can be done to help troubleshoot the system if it needs attention, and how the system needs to be maintained.

I also suggest the local gas supplier be called out, one to verify the system is built and two operates correctly. They will be glad to come out, they do not want any problems to happen with gas systems, for obvious reasons. They hate it when homes are exploded off their foundations, and people get killed.

I also recommend the local heating inspector be called, to verify the system was permitted when installed, inspected for Certificate of Occupancy, and to possibly help explain if there are local codes that require the system as it appears, the water heater controls the furnace.

You should also learn how the CO detector system works, what needs to be done to maintain low CO to keep the system operating properly, and to learn more then you learned on your own, how to reset the system, and more importantly, learn why the system tripped, and how to prevent the system from activating in the future. The CO system is great, and probalbly is being installed more these days. CO is a silent killer.

I wonder how many people have these systems, and figure out how to bypass the detectors because it keeps tripping, like removing the batteries from smoke detectors, and removing the smoke detectors completely.

I really think you need to learn as much about this system as possible, so you know how it should operate, what to do when it dos not operate properly, and to verify that it is built properly.

tkrussell,

Definitely great advice on all counts. I've already called the gas company and they said they'd come out and look at it. When I explained to them what I thought based on what I learned on my own and from help from this board they said that they'd come out to look at it.

Didn't think about the building inspector... I think I'll go that route as well.

As far as the CO detector goes I'm definitely in favor of all sorts of safety guards. I think the one and only time it tripped was when we were having unusually high pressure and wind and the right combination of atmospheric pressure conditions could have caused CO to accumulate around the inlet and caused the CO detector to trip. It only happened once in the last 11 years so I'm not really worried about it unless it starts to happen more frequenty.

Again, thanks for the advice.

Casey

The Gas company came and checked the Gas pressure and all is well. You're right, they came out right away and wanted to be safe than sorry and they do this free of charge.

The gentleman that came also exclaimed that he's never seen a setup like mine. He did assure me that the control unit I described is in no way connected to the furnace but it could be that the wires go to the furnace enclosure to run the wires to another "motor" unit which controls some sort of a vent. Still strange and I don't understand it.

He did recommend that I clean the furnace (normal maintenance) and to call a specialist. That's my next step.

There's more than what you've told us.

This control unit - is a gas pressure switch for a forced air inducton blower. I don't know why you have one, maybe code requirements?

There's CO sensors under your exhaust hood on the top of the hot water tank. It is part of the control loop for the gas valves and the blower unit. Makes sure the flue is open enough and the blower is operating properly.

I'm guessing now... there's more under the hood in the furnace. My guess is they are interconnected in some fashion to use a single blower?

Second guess is that the interlock on the furnace side is improperly connected - as it won't acutuate the gas valve in the funace unless the hot water tank is sensed to be on, thus allowing the blower to fire up.

You need an expert - and insist on having him tell you exactly how it works. More importantly, why does it only work in what appears to be a fault mode? I'd ask them to re-configure it; this time failsafe!

Look here for more... http://www.fieldcontrols.com/manuals.html

I only skimmed enough to get a feel for what you've got going on in there - you can probably look around for the rest of the apparatus and fill us in with more details.

Good luck and keep us in the loop.

Our new man stew may be on to something. If the hot water heater is using the furnace's draft blower for its draft, the pressure switch could turn on the draft when hot water heater came on.

Now, if the furnace controls that turn on the blower for the furnace failed, the furnace may only run when the hot water heater already had the draft blower on. The weird connection may not be the problem. It just confused the issue of the furnace not starting the draft blower.

Might even be able to rat out the blower problem yourself. Chances are though, it is on the control board and very tough to find andfix.

Engineering degree keeps getting in the way... :)

Follow all the wires - take some more pix.

Try to draw out a schematic - might be able to figure it out if we know what all is in the circuits. This stuff is usually simple relay logic (or solid state equivalent).

There's something messed up in the control logic that interlocks out the furnace. I'd be fairly critical of the original installer - while this failure mode is relatively benign, I begin questioning what other failure modes might have been overlooked.

This one's got my attention...

Guessing now... you got one of there?

http://www.fieldcontrols.com/WD_PDFS/GasFurnace30milliWD.zip

I don't know how the "post purge timer" is supposed to work, but I'd guess the blower has to be on for some time before it will allow the gas valve to open.

Depending on the internals of that little beast - I'm guessing the pressure switch on the water heater is backfeeding the furnace circuit - letting it fire the gas valve if the blower is already running and the thermostat calls for heat.

Now I'm going to wait and see what you find out.

Boy this is getting exciting :) What I have looks practically identical to this:

http://www.fieldcontrols.com/instructionmanuals/46285300.zip

I'm going to have to take apart the Furnace to see where the wires are going but I can't do that until Monday (military duty). I can't wait to get back. I have a hunch we're now on to the root cause of this problem.

Casey


P.S. For some strange reason the problem (after 30+ days now) has stopped without me doing anything at all. I suspect this is only temporary until the weather gets real cold again.

OK - keep us posted on your findings. We'll be waiting for your response. This one's been FUN!

By the way - on the military duty - THANKS!

Be careful!

Great, a furnace problem that gets worse when it is cold.

When things are working normal, does the small draft blower, or anything in the furnace, come on when the hot water heater is on? That would confirm my idea that the water heater shares the furnaces draft blower. Thus if the furnace controls failed to start the blower, the furnace would run once the water heater started the blower. It would be like the furnace blower controls failing and the furnace running with the fan in the on position as reported here frequently.

This is an interesting one, I thought the furnace was dependent on the water heater ,for some reason, just did not think of the power inducer. I had a setup similar to this, only in respect to the length of the flue duct work, and had a power inducer with a common flue for both units that would only come on when the water heater came on. My furnace looked very similar to the one in the picture (https://www.askmehelpdesk.com/attachment.php?attachmentid=564&d=1138556306), and if you notice you can see a built in inducer built into the furnace.

So, my guess is that is what they intended to , but for some reason either accidentally or intentionally added the furnace control circuit to the power inducer control circuit.

I wonder if they are trying to control the built in draft inducer in the furnace?

Stew great job, just hope I was able to add something relevant.

Hello Folks. I'm finally getting a chance to revisit this problem. As a refresher, the problem is still such that the Furnace only kicks in when the Hot Water heater goes on. I've even narrowed the behavior further... get this... this problem ONLY seems to happen when the temperature is very cold. If the outside temp is above freezing then I don't seem to have that problem but when the temperature is really cold then the only way to get the furnace going is by forcing the hot water heater to come on by either letting the hot water run inside the house or by going downstairs and raising the dial to a hotter setting.

So... what I've done so far was to clean the furnace. No change. When I opened the furnace to see where those wires went from the water heater it was like a rat's nest of wires in there. I wasn't like originally thought previously that the wires lead to the external blower. The wires actually connected to some sort of control unit inside the furnace and after that I was lost.

At this point the unit is beyond the warrantee period so I'm not sure I can call the builder for repairs. If anyone has any other suggestions to try just shy of calling in a specialist I'd really appreciate it. I'd hate to give up on this one.

Also I'm going to take some more pictures tonight of the wiring inside the furnace and hopefully that will provide a clue.

Casey

OK - we're here when U got more info. Let us know what we can do to help. This one is too fun... :D

I guess Stew is right, the tough ones are more fun. Glad to see him back again. Did you see the question on the sloshing Freon at the ''A'' coil?

Does the furnace have 2 firing rates? It still sounds like the furnace won't run without the inducer. The signal from the furnace isn't starting it, so it only runs when the hot water heater is on. That's my story, and I am sticking to it. It could be the furnace controls work to start the inducer at the low rate, but not the high. Great situation, the furnace won't run just when you need it the most.

I haven't forgotten about this. I've been getting home late and the lighting in the basement has been poor. So every picture I've taken so far is horrible and doesn't really show what I want it to show. So I've gotten some special lighting equipment from a friend to disperse the light (soft light) so I can take a good shot of this beast. Otherwise I really can't explain what or where all the wires go. So as soon as I get home I'm putting my photography makeshift studio in the basement :)

Casey