interesting issue..... need gas furnace troubleshooting help
#1
01-02-15, 09:51 PM
interesting issue..... need gas furnace troubleshooting help
Greetings all!
Woke up this morning to find out that my heating system is not turning on. Sentry s-90 dp gas hot water system, 1 zone.
I spent the last few hours reading and researching, putting pieces together but there is still something missing.
The problem:
When the thermostat calls for heat, the relay clicks but the damper does not move, therefore heat does not go ON.
But....
When I drain some hot water and the boiler gets filled with fresh cold water and the boiler water temp drops below the specified 180 degrees, the damper opens, and heat goes ON until the 180 is reached. This leads me to believe that the rollout switch and the blocked vent safety switch are OK since they allow the the system to turn ON. This also leads me to believe the damper is OK because it does open and close when the system calls for internal water temp of 180.
Here is what my plan is for tomorrow anyway:
1. Verify the rollout switch was not tripped with a multimeter. Just to be safe, try to jump it, see if that helps.
2. Verify the blocked vent switch was not tripped, try to reset it, make sure it is not an open circuit, try to jump it.
3. Verify 24VAC across relay B1 and B2.
Now....
What additional steps are involved in the sequence when the thermostat calls for heat vs. when the furnace itself calls for heat (to keep water temp at 180)???
Does this point to the relay being the faulty part?
Also...is the damper really necessary? Is it simply for efficiency? I'm thinking if I can't resolve the problem right away, maybe I can remove the flap from the inside so that it is always open and jump the damper switch so that it thinks its open, in turn letting the gas valve go on. Thoughts?
Thank you
Woke up this morning to find out that my heating system is not turning on. Sentry s-90 dp gas hot water system, 1 zone.
I spent the last few hours reading and researching, putting pieces together but there is still something missing.
The problem:
When the thermostat calls for heat, the relay clicks but the damper does not move, therefore heat does not go ON.
But....
When I drain some hot water and the boiler gets filled with fresh cold water and the boiler water temp drops below the specified 180 degrees, the damper opens, and heat goes ON until the 180 is reached. This leads me to believe that the rollout switch and the blocked vent safety switch are OK since they allow the the system to turn ON. This also leads me to believe the damper is OK because it does open and close when the system calls for internal water temp of 180.
Here is what my plan is for tomorrow anyway:
1. Verify the rollout switch was not tripped with a multimeter. Just to be safe, try to jump it, see if that helps.
2. Verify the blocked vent switch was not tripped, try to reset it, make sure it is not an open circuit, try to jump it.
3. Verify 24VAC across relay B1 and B2.
Now....
What additional steps are involved in the sequence when the thermostat calls for heat vs. when the furnace itself calls for heat (to keep water temp at 180)???
Does this point to the relay being the faulty part?
Also...is the damper really necessary? Is it simply for efficiency? I'm thinking if I can't resolve the problem right away, maybe I can remove the flap from the inside so that it is always open and jump the damper switch so that it thinks its open, in turn letting the gas valve go on. Thoughts?
Thank you
#2
01-03-15, 10:41 AM
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I'm not familiar with your boiler but from the sound of things, I believe you may have a circulator relay problem. Good clear pictures both from a distance for an overall look & closer up so we can see contols better would help.
#3
01-03-15, 11:45 AM
Update:
Rollout switch tested good, blocked vent switch tested good.
When the thermostat calls for heat, i am not getting 24VAC at B1-B2 which would explain why the damper doesnt open right?
But when fresh cold water is let into the system and boiler water temperature drops under 180, I do get 24VAC at B1-B2, damper opens and burners goes on until the 180 is reached.
Do the thermostat and aquastat send 24VAC to the damper 2 different ways which would explain the above observation?
I also tested the voltage at the circulator supply wires and it does get 120V. Should the circulator go ON and I should hear/feel it working as soon as the relay gets the call for heat from the thermostat OR does the damper open first and then circulator goes ON?
No pics at the moment but will take some later.
Rollout switch tested good, blocked vent switch tested good.
When the thermostat calls for heat, i am not getting 24VAC at B1-B2 which would explain why the damper doesnt open right?
But when fresh cold water is let into the system and boiler water temperature drops under 180, I do get 24VAC at B1-B2, damper opens and burners goes on until the 180 is reached.
Do the thermostat and aquastat send 24VAC to the damper 2 different ways which would explain the above observation?
I also tested the voltage at the circulator supply wires and it does get 120V. Should the circulator go ON and I should hear/feel it working as soon as the relay gets the call for heat from the thermostat OR does the damper open first and then circulator goes ON?
No pics at the moment but will take some later.
#4
01-03-15, 12:23 PM
Member
What model aquast are you using?how long has this benn going on?
Geo
Geo
Last edited by Geochurchi; 01-03-15 at 12:50 PM. Reason: More questions
#5
01-03-15, 12:50 PM
Geo,
This is the L8148E aquastat relay. From searching around on the net, it seems this one does not have a low limit feature. Stopped working since yesterday morning.
Im going to pick up a pump just in case as well but would this point to the Taco pump? Would the pump not engaging prevent the damper from opening?
Also I currently have the Taco 007-BF5-J which is the bronze one.....of course none of the stores have it. Is it safe to replace it with the 007-f5 cast iron one?
Thanks
This is the L8148E aquastat relay. From searching around on the net, it seems this one does not have a low limit feature. Stopped working since yesterday morning.
Im going to pick up a pump just in case as well but would this point to the Taco pump? Would the pump not engaging prevent the damper from opening?
Also I currently have the Taco 007-BF5-J which is the bronze one.....of course none of the stores have it. Is it safe to replace it with the 007-f5 cast iron one?
Thanks
#6
01-03-15, 01:12 PM
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Location: Delaware, The First State
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Bronze is for domestic water or other open loop applications. I see no need for a bronze circulator. Before you replace a circulator, what is the pressure on the boiler? Is the circulator motor hot?
#7
01-03-15, 01:29 PM
Pressure is right around 200 which is identical to the (working) furnace right next to it which is for the 2nd floor apartment.
The circulator is hot to the touch as well as 5 feet of the return pipe coming into it.
Thanks
The circulator is hot to the touch as well as 5 feet of the return pipe coming into it.
Thanks
#8
01-03-15, 01:45 PM
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Join Date: Jan 2005
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I'm a bit confused. If the return piping is hot I'm thinking you should have heat. Is the supply piping hot? What kind of emitters do you have (cast iron radiators, fin tube baseboard, etc.) & are they hot?
Pressure of 200? 200 what? Normal boiler pressure should be around 12-20 psi or 30-45 ft. of water column.
Pressure of 200? 200 what? Normal boiler pressure should be around 12-20 psi or 30-45 ft. of water column.
#9
01-03-15, 01:45 PM
Member
I agree with Grady,on the Bronze. Cir,here is a link to the aquast, explaining how it should work.
http://s3.supplyhouse.com/manuals/13..._PROD_FILE.pdf
Geo
http://s3.supplyhouse.com/manuals/13..._PROD_FILE.pdf
Geo
#11
01-04-15, 12:32 PM
Sorry, system pressure when burners are ON is ~200 kPa which is around 28psi. When burners are off the system pressure is around 17psi.
Problem solved, it was the circulator, I guess it burnt out. What gave it away is the 120VAC across the 2 terminals which go from the relay to the pump. When the thermostat was calling for heat, relay sent 120V but compared to another circulator, I did not feel any vibrations even though the circulator was hot.
Replaced the circulator and all good.
What confused me and made me thing that the aquastat is bad is the following:
Reading another post on here I saw that the order of events is as follows:
1. Thermostat calls for heat
2. Relay sends 24V to the damper across terminals B1 and B2
3. Damper opens
4. Burners go ON
This should be clarified.... The relay will send 24V ONLY when the system temperature is under what the aquastat is looking for. In my case the aquastat keeps the system temp at 170 degrees so if the system is already at 170, the relay will not tell the damper to open up, it will just turn the circulator on and push the water through if the house thermostat is calling for heat.
I was under the impression that the damper has to open every time the house thermostat calls for heat....now I have an extra relay.
Thanks for you help guys!
Problem solved, it was the circulator, I guess it burnt out. What gave it away is the 120VAC across the 2 terminals which go from the relay to the pump. When the thermostat was calling for heat, relay sent 120V but compared to another circulator, I did not feel any vibrations even though the circulator was hot.
Replaced the circulator and all good.
What confused me and made me thing that the aquastat is bad is the following:
Reading another post on here I saw that the order of events is as follows:
1. Thermostat calls for heat
2. Relay sends 24V to the damper across terminals B1 and B2
3. Damper opens
4. Burners go ON
This should be clarified.... The relay will send 24V ONLY when the system temperature is under what the aquastat is looking for. In my case the aquastat keeps the system temp at 170 degrees so if the system is already at 170, the relay will not tell the damper to open up, it will just turn the circulator on and push the water through if the house thermostat is calling for heat.
I was under the impression that the damper has to open every time the house thermostat calls for heat....now I have an extra relay.
Thanks for you help guys!
