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Reznor garage heater wont light. Why?

Customer Question

I have a Reznor V3 T Core2 MDL no UDAP45 garage heater that won't light. The control card has a lit solid green light that starts flashing green when it tries to light. What's wrong?

Submitted: 5 years ago.
Category: HVAC
Expert:  Tom replied 5 years ago.

Tom :

Hi.

When it calls for heat...[green light flashing]...does the vent motor start? [small exhaust motor inside cabinet]

JACUSTOMER-mejyyh48- :

Unit started working again yesterday morning but then quit again yesterday afternoon. It is not working this morning. When the unit was working yesterday morning, it had an exhaust-like smell so I took the vent cap off and inspected. I didn't find any obstructions so I put the exhaust cap back on. Now, the answer to your question. I checked the unit this morning and when there is a call for heat, the vent motor does start and continue running. I watched the green light on the IC board and it flashes 3 times. Then there is a 1 second delay and then it repeats. Any ideas? I'm wondering if there is a clog in the natural gas line?

Tom :

3 flashes is an open hi limit switch or rollout switch open. The rollout on your 45 is a manual reset...so it wouldn't light again if it tripped until you reset it...

The high limit is an auto reset so it would try to go again after it cooled down.

Is this an old or new installation?

How long does it run before it shuts down? Was the unit ever converted from natural to LP or vice versa... and does the main fan run OK?

If it won't light at all now ... and you're getting three flashes..it's probably an open limit switch. Check the wire connections to the limit and make sure they are good. Also check all plug in connections and in the wire harness.

Here is a link to the install manual if you don't have one. Page 31 shows the location of the high limit sensor. You can pull the wires off and check for continuity with an OHM meter if you have one. If it's open circuited it will have to be replaced.

We still need to figure out why it's tripping...were you able to see through the entire vent pipe? Also check the heat exchanger for cracks...(inspect through the front louvers) if it's been in service for awhile.

JACUSTOMER-mejyyh48- :

I had to work late yesterday and didn't get a chance to look at unit until this morning. Answers to your questions about the unit. I bought the house back in August so that's as far back as I know. House was built in 2005 and looks like the unit was new when the house was built. Unit has worked okay until recently (Sept - Present). I just checked the limit control and flame rollout switches with an OHM meter and both checked at 0.1 OHMS. I noticed the thermal wrap on the flame rollout switch near the heat exchanger had slid off and was exposing the copper wire. I slide the thermal wrap over the exposed copper conductor and reinstalled the flame rollout switch. When I powered the unit up, it started working. Also, I visually inspected the heat exchanger and didn't find any cracks or rust . . . but quite a bit of dust which might be what I was smelling last time the unit was working. Anyway, I'd like to give the unit a day to see if it keeps operating. Can the limit switch work intermittently or do they usually fail once and quite working permanently?

Tom - Ok

JACUSTOMER-mejyyh48- :

Heater is working fine now. Problem must have been bad electrical connection to limit switches. Thanks for your help!

Tom, HVAC Technician
Category: HVAC
Satisfied Customers: 770
Experience: 16+yrs HVAC/R service. Residential Commerical Industrial
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Expert:  Tom replied 5 years ago.

You are welcome. Glad it's working. As for the limit...very seldom would one be intermittent..usually good or bad. You are correct..the wire connection was probably at fault..

Intermittent problems like that ...I usually start tugging on wires..cleaning connections..unplugging and rep-lugging harnesses....good call..

Let me know if you need further assistance.

Thank you!

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