DGAT intermittently lock-outs

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I have a 10 to 12 year old Coleman-Evcon furnace (DGAT070BDC) and just in the last month or so it started locking out. This is my week end lake place and I came into into this problem my last time down. The house was cold and the T-stat was calling for heat but only the purge pump was running. Reset the T-stat and it seemed to do fine running all night and getting up to temperature. But I caught it in action the following evening. I noticed the purge pump running but the burner not coming on and it locked out several tries in a row. First, the purge pump would come on and run for a bit as usual followed by the ignitor stick firing up and glowing red, then the gas valve opens and the burner ignites for 5 - 10 seconds only to go out. After 3 missed tries on the burner it just stays there locked out until turning the T-stat off and back on. I was there for 3 days and it ran normally most of the week end but it locked out 5 or 6 times. Had tech out on third day and he found 2 gas leaks (I had smelled gas when I first opened the house) - one on a plug on the side of the gas valve and one in the low pressure regulator which he replaced. He said the intermittent ignition problem had to be due to a bad ignition control module and then proceeded to tell me my heat exchanger was bad and I needed a new furnace.

I know a bad heat exchanger is a far more serious problem than the lock-out but I want to state up front I believe this tech was trying to rail road me in to a quick purchase. I talked to some DIY friends and they reminded me that the surest way to know if an exchanger is bad is if when the blower comes on the burner flame dances around. I am pretty certain this is not the case and when I head back down later this week I plan to double-check this so my concern is back on the ignition problem. I picked up a new ICM and after reading several posts on this site I have a feeling the ICM is not the prime suspect although it will be easy to replace. My first question is how likely is a leak in the low pressure regulator a possible cause in an intermittent problem like this? It could be the tech already fixed my problem but I left shortly after he did and didn't get a good feel if the lock-outs had stopped.

What other things should I check when I am down later this week? I wondered about cleaning / or testing the flame sensor but when I mentioned this to the tech he said that if it were the flame sensor the problem wouldn't be intermittent.

Thanks in advance for any help and kudos to a great site!

kc

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(What other things should I check when I am down later this week? I wondered about cleaning / or testing the flame sensor but when I mentioned this to the tech he said that if it were the flame sensor the problem wouldn't be intermittent.)

With everything else checked I would clean that sensor. In fact cleaning the sensor seems to clear up some problems like you have. Fine steel wool seems to work best according to my informed sources. Easy does it and do not break anything while cleaning it. Intermittent problems are tuff to find.

hvac1000

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I appreciate the reply hvac. I know what you mean about intermittent problems and even if the furnace runs good for a day or two I don't feel I can trust it. It did this last time down at least running for a day. I plan to winterize the trailer when I am down next so that I can leave the furnace off and not have to worry about the place freezing up. I usually just turn the t-stat all of the way down but I don't want to take the chance. I hope I do some good this week and things look up.

kc

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Hi,

The Sensor can be intermittant. Looking for a dancing flame IS NOT conclusive for a cracked heat exchanger.

Do not touch the remote sensor or hot surface ignitor with your bare hands or fingers.

Clean the sensor gently with steel wool and be sure it is positioned correctly.

Check the porcelin shroud of sensor for any cracks and make sure the wire is connected tightly.

Also, check positioning of hot surface ignitor and check for tight wire connections.

IF the sensor does not have any cracks, after cleaning, it is usually fine.

I would suspect the hot surface ignitor (HSI) the most.

The best a homeowner can do on the heat exchanger is run a cycle to get chamber HOT for expansion. Shut it off and use a mirror and bright light to look for cracks (do not get burned).

Also, place blower in continous ON mode for hi speed and look for dancing flame.

Also, making sure you have a working CO detector close by.

Take care and best wishes,
Robert

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Thanks for the tips Robert!

The HSI does come on and glows red and the gas does ignite. But does the HSI have to stay hot for the gas to stayed burning? Would the HSI do something differently when these lock ups happen or cause the flame to go out? I am just trying to find something to look for when I am down and the flame goes out again. This is going to be tricky to corner since it doesn't happen consistently.

I talked with my wife and we decided it would be a good idea to get one of the CO2 detectors for the trailer. Any advice on a good unit?

Thanks for your help!!!

kc

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Most often, when the burner ignites and goes out after 5-10 seconds, it is the HSI or Remote Sensor.

Most of the time, if it's the Sensor, it only needs cleaning.

Check the Sensor close for cracks. if none found, clean it good and see if that takes care of it.

IF not, then check to see if HSI is continously receiving 120 vac for 35 seconds.

IF the HSI is losing power, suspect the Ignition Module.

If not, then you would have to check amperage pull of HSI.

When it goes out, have your Meter leads on the Gas valve terminal wires and see if they lose the 24-28vac signal.

Thanks,
Robert