Old mercury operated thermostat replacement

Thread Starter

marko1polo

Joined Oct 10, 2016
11
I am no electrician , and I don't know if this is the proper area for discussion , but here it goes anyhow ....

Yesterday , I lost heat on the first floor . The house is old and has a mercury operated thermostat on the main floor and 1 in the basement . With a broken oil tank gauge , I figured I was out of oil and got more heating oil . The cellar thermostat worked , but the main floor didn't ! So I dialed the thermostat for more heat and nothing ! The cellar thermostat when adjusting the desired heat setting , you hear a click signifying that the oil burner will run thus increased the water temperature for more heat . No click on the main floor ! So I figure the thermostat finally went ! Taking the old one off the wall , I see that only 2 wires come out of the wall for this manual "heat only" thermostat ; a red and white wire . Went and got a new thermostat to replace it . Seems pretty simple , however the existing plate that takes the red & white wire that has been that way for a gazillion years confused me as the white wire was connected to the screw marked "R" , and the red wire was connected to the screw Marked "W" ! I have heard of old home wiring that had colors that performed just the opposite , and I'm losing heat fast ! My question is .... Do I connect these wires to the new thermostat as the old one has been , or do I go red to red , and white to white ? If they are reversed , will I do damage to the system some how ? Please help ! The thermostat that is old is a Honeywell CT 87A 4447 1 !
 

Ylli

Joined Nov 13, 2015
1,083
The old thermostat was simply a spst switch. didn't make any difference which way the wires were attached. That may not be the case with the new thermostat. What make/model is the new one? Is it also just a two wire unit?
 

Thread Starter

marko1polo

Joined Oct 10, 2016
11
The old thermostat was simply a spst switch. didn't make any difference which way the wires were attached. That may not be the case with the new thermostat. What make/model is the new one? Is it also just a two wire unit?
To Ylli ... the new one is also a 2 wire and us compatible with the old thermostat . The new Honeywell CT87N/CT87K . The CT87K is for a 2 wire setup . So I hooked it up the same as the old one ; white to red , and red to white , and now I hear the click noise when I change the temperature higher or below the room temperature , The old one did nothing ! However , with the cover off on the reset button on the oil burner , the contact arm makes the motion , yet the oil burner won't fire up ! At least thus far I'm getting the click noise . If I switch it to red to red & white to white , will I screw something up and or damage the new unit ? Also there are (4) settings on the inside of the temperature cover on the new unit to chose from called cycle rate switches that are titled "Steam or Gravity" , "High Energy Warm Air" , "Gas or Oil Warm Air" & "Electric Warm Air" , all with Switch 1 and Switch 2 on and off settings ! It's an oil firing oil burner that heats the water to the radiators . I tried the 1st 2 , but it didn't seem to do anything ! Still at a loss here !
 

Ylli

Joined Nov 13, 2015
1,083
If it is a simple two wire thermostat, then red/wht shouldn't matter . You probably want the thermostat set to #2.

If you can find where those red and white wires terminate at the boiler, try shorting then at the boiler and see if it comes on. Will tell us if the problem is in the thermostat and associated wiring, or in the boiler itself.

Another thought -- is this a single zone or multi zone? If multizone, could get more complicated, the thermostat you are replacing might just control a valve.
 

Thread Starter

marko1polo

Joined Oct 10, 2016
11
If it is a simple two wire thermostat, then red/wht shouldn't matter . You probably want the thermostat set to #2.

If you can find where those red and white wires terminate at the boiler, try shorting then at the boiler and see if it comes on. Will tell us if the problem is in the thermostat and associated wiring, or in the boiler itself.

Another thought -- is this a single zone or multi zone? If multizone, could get more complicated, the thermostat you are replacing might just control a valve.
With the cover off on the reset button box , there is what seems to be (2) small coiled transformer looking setup . The left one is for the downstairs/cellar thermostat , the right for all of upstairs where there's no heat . Each one has it's own "flap" or a "spoiler like on a car" that is seated closed , and when making a thermostat adjustment for more heat , it opens and the oil burner starts hence heat . The left one is fine , and the right makes the motion using the new thermostat , but doesn't fire up the boiler ! I'm on state help and can't afford a serviceman to address this ! I love the winter but really do wish it were spring or summer ! Thank you thus far Ylli ! I tried placing a wire across the red & white wire at the burner and there was no spark or any result by the way !
 

LesJones

Joined Jan 8, 2017
4,171
Some good pictures of the inside of what you call the "reset button box" might help. It sounds like the things you desribe as transformers could be relays. Can you also confirn that this is the sort of heating system where the poiler heats water which then heats radiators. (As opposed to the type that heats air that is ducted round the building.) Assuming it is the water based system there will probably be motorised valves that control the flow of water to different areas of the building. If so one of these may be faulty. Do you know if your system has motorised valves and if so where they are located. The way things are done in the UK they are normally near the boiler. As you do not give any idea of your location none of us know where you are. (People located in your country are more likely to know how things are done there.)

Les.
 

Thread Starter

marko1polo

Joined Oct 10, 2016
11
Some good pictures of the inside of what you call the "reset button box" might help. It sounds like the things you desribe as transformers could be relays. Can you also confirn that this is the sort of heating system where the poiler heats water which then heats radiators. (As opposed to the type that heats air that is ducted round the building.) Assuming it is the water based system there will probably be motorised valves that control the flow of water to different areas of the building. If so one of these may be faulty. Do you know if your system has motorised valves and if so where they are located. The way things are done in the UK they are normally near the boiler. As you do not give any idea of your location none of us know where you are. (People located in your country are more likely to know how things are done there.)

Les.
Thanks again Les ! Here are some pictures of what I was trying to explain from Fairfield CT , USA ...
Pic 1 : Shows that only (2) wires come out of the wall to power the new 2 wire Honeywell thermostat ... Pic 2 : Is kind of blurred , but shows that the old setup which was that way for decades , has the red wire going to the "W" , and the white wire going to the "R" ... Pic 3 : Shows the reset red button , the (2) left for the basement thermostat coil/flap contact that seems to work & the right one for the ground level thermostat which is not working . Also to the upper right of this "reset button box" , is the white and red wire hookup from the ground level non-working thermostat (maybe) , the "flapper/contacts are shown in gray , left lower one is the basement thermostat that is working , and the right upper one is for the ground level thermostat that works , but does not "ignite" the burner for more heat ! ... Pic 4 : Shows a bit better , the red and white wire from the ground level thermostat ... Pic 5 : Another view ... Pic 6 : Shows the left side of the "reset box's" contents . Also , the hot water still works for the dishwasher and the shower on the ground level , just not getting the hot water to all ground level and 2nd floor radiators ! Note : the ground level thermostat controls ALL ground level and 2nd floor bedroom radiator heat ! Looking forward to more solutions ! Thank you again and thanks to others that have elaborated on this matter !!!
 

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Ylli

Joined Nov 13, 2015
1,083
The two items where you can see the windings (upper right and lower center) are transformers. The two devices in the center appear to be relays. I have no idea what that box-like item is on center left.

You have been talking about two thermostats. I only see one set of red and white wires coming in at the upper right. Is there a second set i don't see?

So the downstairs thermostat activates the left relay, and the boiler comes on and produces heat. The ground floor thermostat appears to activate the right relay but the boiler does not come on, is that correct? (Trying to isolate where the problem might be.)

Be careful working inside this box. Line voltage is accessible. Keep fingers clear when you have the power on.
 

Thread Starter

marko1polo

Joined Oct 10, 2016
11
The two items where you can see the windings (upper right and lower center) are transformers. The two devices in the center appear to be relays. I have no idea what that box-like item is on center left.

You have been talking about two thermostats. I only see one set of red and white wires coming in at the upper right. Is there a second set i don't see?

So the downstairs thermostat activates the left relay, and the boiler comes on and produces heat. The ground floor thermostat appears to activate the right relay but the boiler does not come on, is that correct? (Trying to isolate where the problem might be.)

Be careful working inside this box. Line voltage is accessible. Keep fingers clear when you have the power on.
Thank you Ylli ! Yes you are correct ! Right relay moves when actuated by the ground level thermostat , but the oil burner does not fire up ! About electricity that totally scares me ? I am super careful ! Thanks again ..... Mark
 

LesJones

Joined Jan 8, 2017
4,171
I am faily sure that the two items you are talking about are relays but the way they are mounted I can't see the contact assembly on them. If I understand waht you are saying correctly I thing the contacts on the right hand relay are faulty. Can you confirm that when the new thermostat is set above the temperature of the room it is in (I.E The heating needs to be on.) that the flapper as you call it is pulled agains the coil part ? Can you also confirm that when the thermostsat is set below the room temperature (I.E no heating is required.) that the flapper is NOT pulled against the coil part of the realay ? If this is the case then the thermostat is working. If you can find a manufacturers name and model number on the control unit then it may be possible to fined a schematic or manual online which would be a great help. It is possible that the relay does not fire up the boiler directly. It could drive a motorised valve which has a contact in it that fires up the boiler when it has reached it's fully open position.
One last point for now. Some types of relay plug into the board and others are soldered in. I can't tell this from the pictures. Can you see which type of relay they are ?
Les.
 

Ylli

Joined Nov 13, 2015
1,083
What Les said. Beginning to sound like a bad set of contacts on then relay. Turn power off at the switch for the boiler and then see if you can see/access the contacts on the relay.
 

Thread Starter

marko1polo

Joined Oct 10, 2016
11
I am faily sure that the two items you are talking about are relays but the way they are mounted I can't see the contact assembly on them. If I understand waht you are saying correctly I thing the contacts on the right hand relay are faulty. Can you confirm that when the new thermostat is set above the temperature of the room it is in (I.E The heating needs to be on.) that the flapper as you call it is pulled agains the coil part ? Can you also confirm that when the thermostsat is set below the room temperature (I.E no heating is required.) that the flapper is NOT pulled against the coil part of the realay ? If this is the case then the thermostat is working. If you can find a manufacturers name and model number on the control unit then it may be possible to fined a schematic or manual online which would be a great help. It is possible that the relay does not fire up the boiler directly. It could drive a motorised valve which has a contact in it that fires up the boiler when it has reached it's fully open position.
One last point for now. Some types of relay plug into the board and others are soldered in. I can't tell this from the pictures. Can you see which type of relay they are ?

Les.
What Les said. Beginning to sound like a bad set of contacts on then relay. Turn power off at the switch for the boiler and then see if you can see/access the contacts on the relay.
Problem Solved
!! The next door neighbor who is a plumber / hvac mechanic has made the ground level heat work again ! He told me a bunch of things that I don't understand , but this is what we did .... the red and white wire that went to the ground level thermostat had no power ! He told me that it was kind of useless to heat the cellar (as we needed a fast cure) , so we took the wire off the cellar thermostat and brought it through the ceiling to the oil burner area , and connected it to the ground level thermostat ! He disconnected the regulator (I think he called it) from the ground level one , and connected the cellar one and BOOM the burner went on and once again began to heat the ground level and 2nd floor radiators !!! Just in time for the Superbowl , but most importantly just before the next cold snap coming to us from up past Canada ! Best of all , problem solved in 45 minutes and at no cost ! Thanking the heavens for good neighbors ! Thank you ALL for the concern and the time you took , I greatly appreciate it ! This site is truly amazing ! God Bless to ALL !!! .............. Mark
 

MisterBill2

Joined Jan 23, 2018
17,743
If it is a simple two wire thermostat, then red/wht shouldn't matter . You probably want the thermostat set to #2.

If you can find where those red and white wires terminate at the boiler, try shorting then at the boiler and see if it comes on. Will tell us if the problem is in the thermostat and associated wiring, or in the boiler itself.

Another thought -- is this a single zone or multi zone? If multizone, could get more complicated, the thermostat you are replacing might just control a valve.
Yes indeed! If the downstairs thermostat makes the heat work for downstairs then the fault is not with the furnace, but since it seems like there must be two zones, the fault would be with the zone controller. If the working portion of the system makes the boiler come on and the circulation pump run, then probably the fault is in the zone control valve for the zone that is not working. Often each zone valve has a switch that enables the boiler when the valve is operated. The valve may have a manual over ride lever, in which case you can operate that and get heat until the valve can be either repaired or replaced. I experienced exactly the same problem in the 4-zone heating system for an apartment building that I service.
 
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