garage heater help

[JB @ C and L Machine]

I had a Reznor gas fan heater insatlled about 2 years ago and it has a problem coming back on after it comes up to temp. I thought it was the cheapo theromstat I bought but I installed a new one and it seems worse. any thoughts JB

 

[Bill Stockard]

Does it have a standing pilot light?



I have a 100K BTU LP gas unit heater controlled by a thermostat in my toy house. I had intermittent problems with it coming back on which was caused by too low a flame on the pilot. I cleaned the LP "goop" out of the pilot flame orfice with spray brake cleaner which fixed it.



Bill

 

[mgoncalves]

If changing the T-stat changed your symptoms from before, you should isolate the furnace from the stat and proceed when you know which way to go.



On 99% of my service calls, the first thing I do is jumper out the stat.



Matt

 

[ToolManTimTaylor]

Standing pilot ... = Thermocouple ??

 

[JB @ C and L Machine]

ok. . heres some info I found out. . It doesnt have a standing pilot... we have had some lower temps here (teens and 20's) in the mornings and that when it acts up the most. Yesterday it was around 50 and the heater and t-stat worked fine. I talked to the guys that installed it and he said its either a bad curcit board or a sensor(I forgot what he called it)needed to be cleaned. This couldn't happen at a worse time. I'm painting my car on New Years day. JB

 

[HoleshotHolset]

If it doesn't have a standing pilot - the sensor you are talking about could be a 'flame sensor'. I'm not an HVAC guy, but I've learned a lot about that stuff here on the TDR.



Here's the startup sequence (on my furnace, anyhow... yours will be sorta similar to this):

1) 'Stat calls for heat

2) Draft inducer (if so equipped... ) fires off

3) Spark (or hot surface... ) ignitor fires off

4) Pilot flame ignites

5) Flame sensor verifies good pilot ignition

6) Flame sensor causes gas valve to open for main ignition - then it's mucho gas/flame time!



Step 4 doesn't happen in other furnaces - just my old Carrier. Step 5 happens after main ignition on other furnaces... if the flame sensor is dirty/bad - main ignition won't last very long.



Sometimes you can clean the flame sensor with some steel wool or light sandpaper. On my furnace... the pilot light orifice was clogged up with crud since the non-standing pilot light was inadequate - causing the ignitor to continue to operate and therefore - the furnace never got main ignition.



I swapped out the pilot light/flame sensor assembly on my furnace and it has been running great for over 300 hours now.



Matt