Gas furnace--no heat, no fan. Thermostat?
#1
03-18-18, 12:30 PM
Gas furnace--no heat, no fan. Thermostat?
we have a Lux manual mechanical heat-only thermostat with just two wires (red and white) of the four in the wall hooked up to it. The gas furnace has recently stopped working--no fan, no heat. Thinking (hoping) it might be a thermostat problem, we disconnected the two wires and removed the thermostat, then twisted the red and white wires together and still nothing. Does this mean it's time to call the HVAC guy, or is there something else a homeowner can do in the basement? Thanks.
Forgot to mention: the pilot light is lit.
Forgot to mention: the pilot light is lit.
Last edited by DaveLS; 03-18-18 at 12:48 PM. Reason: Omission
#2
03-18-18, 12:47 PM
Group Moderator
Connecting the two wires together will bypass the thermostat.
If the furnace doesn't start then.... the problem is at the furnace.
You can go down to the furnace and make sure the service switch is on and that it has 120vac.
If propane.... do you have propane ?
You can post the make and model number if you want further help. They can be found on an ID tag inside on the side wall and near the burner.
Pictures are always very helpful...... How-to-insert-pictures
If the furnace doesn't start then.... the problem is at the furnace.
You can go down to the furnace and make sure the service switch is on and that it has 120vac.
If propane.... do you have propane ?
You can post the make and model number if you want further help. They can be found on an ID tag inside on the side wall and near the burner.
Pictures are always very helpful...... How-to-insert-pictures
#4
09-25-18, 12:51 PM
More info
I managed to successfully delay progress on this until now. I think the problem is the gas valve. The fan works (runs if plugged into an extension cord), there's gas (pilot works), but when the wires from the thermostat are crossed, the valve isn't opening to get gas to the burner.
I am attaching some pics.
Can gas valves be serviced? I see Robertshaw valves for sale that look very similar to this one, so it looks like it'd be possible to replace. I'm thinking this isn't a job for a homeowner, though.
Thanks for any advice.
I am attaching some pics.
Can gas valves be serviced? I see Robertshaw valves for sale that look very similar to this one, so it looks like it'd be possible to replace. I'm thinking this isn't a job for a homeowner, though.
Thanks for any advice.
Last edited by PJmax; 09-25-18 at 07:01 PM. Reason: cropped/resized pictures
#5
09-25-18, 07:07 PM
Group Moderator
Wow..... that's a dinosaur. Standing pilot. No online service info. Can't find company either.
Doubtful it's a bad valve. More likely a defective 24vAc transformer.
You need to check the white and black wires on the valve for 24vAC.
Doubtful it's a bad valve. More likely a defective 24vAc transformer.
You need to check the white and black wires on the valve for 24vAC.
#6
09-25-18, 09:36 PM
Dinosaur indeed, lol, and thanks very much for the info. I do see a transformer-looking thing at upper left from where the black/white wires come. Will it be 'on' all the time so the voltage can be checked? Might be a lot easier for a DIYer to swap a transformer than to swap a valve.
#7
09-25-18, 09:42 PM
Group Moderator
It looks to be live all the time. If you don't measure the 24vAC at the gas valve. Look for the input wires to the transformer and make sure they have 120vAC on them.
#9
09-25-18, 10:02 PM
Group Moderator
A transformer is good or bad. If the voltage went down slowly..... the transformer would be smoking.
#13
09-26-18, 04:15 PM
Latest:
The transformer is putting out 27 volts, so it seems fine.
Because it was easy to do and cheap, and because the existing one looked a little ragged at the tip, I replaced the thermocouple with a new one. No difference.
Anything else it could be besides the gas valve?
The transformer is putting out 27 volts, so it seems fine.
Because it was easy to do and cheap, and because the existing one looked a little ragged at the tip, I replaced the thermocouple with a new one. No difference.
Anything else it could be besides the gas valve?
#14
09-26-18, 09:32 PM
Group Moderator
That gas valve only uses the thermocouple to hold the pilot flame on. It's a 24vac valve directly controlled from a thermostat.
Ok.... transformer good. Now set the thermostat to heat. Measure from black to red at gas valve. You should see 24vac there. If you do..... then the valve appears defective. If you don't measure 24vac..... your thermostat is not working correctly.
Ok.... transformer good. Now set the thermostat to heat. Measure from black to red at gas valve. You should see 24vac there. If you do..... then the valve appears defective. If you don't measure 24vac..... your thermostat is not working correctly.
#15
09-27-18, 10:13 AM
Thanks very much for the additional info. I assume 'thermostat' refers to the wall thermostat in the house, and that malfunctioning would mean it's not completing the circuit via what I think is a mercury switch. My sister (who lives in the house that we co-own) has taken the opportunity to request that the utility company come and look at the furnace, so there'll be a few-day delay in the process until that happens.
#16
10-02-18, 11:10 AM
A PG&E (util. co.) guy came by and checked gas and power and Dx'd it as a bad valve and said he thought it'd be easy enough to replace ourselves. This one https://www.robertshaw.com/Products/...cat=2147484264 looks close to identical. The guy also suggested buying a used one at 1/4 the cost of new. Any ideas about where to find one?
#17
10-02-18, 04:19 PM
Group Moderator
Sorry.... I disagree with your utility repairman.... a gas valve is not considered a DIY repair.
