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I have a very similar problem with my Napoleon HD40 fireplace to what another user had posted on. My fireplace is using a Dexen 6K module and 6003 3v valve. The pilot ignites fine using the wall switch with either the transformer or 3v battery pack. However the main burner never lights up. I can also bypass the wall switch at the fireplace by shorting the SW1 contacts together . . . giving me the same result. The voltage from TP -> TH/TP is about 480mv after the pilot has been on for a minute or so. If I pull the TH wire from the valve there is no change. So I'm unsure if a) the ignition module isn't sending the TH wire what it needs or b) if the valve itself is defective. How can I tell? What reading should I have at TH on the valve?

  • Is the gas valve actually opening? What is the resistance across the coil terminals of the main valve? Oct 2, 2017 at 23:50
  • I'm not sure how to tell if the valve is opening. Wouldn't the main burner ignite if it was? Also, which terminals at the valve (TP, TH and TH/TP) should I be measuring . . . . and what should I expect to find if it is good or defective? Oct 4, 2017 at 2:54

2 Answers 2


I ordered a new ICM and that fixed the problem. In checking the voltages at the valve TH to ground is now 1.92v. Also, the red and green LEDs on the battery relay are now brightly illuminated. With the defective ICM they were very dim. Thanks for all your input. Hopefully this will help others in the future.


In millivolt systems which use a mercury switch the problem is that the switch was designed as 125- 50 VA operation not at 480 mv. The switch contacts need to be cleaned up! Remove the switch from the fireplace. Make a jig with a 20 watt bulb and a 110 volt source and have the bulb turned ON and OFF with a flame source (BBQ or torch). With a voltmeter you will find that the contact resistance is now below 1 ohm when it was some 60 ohms in my system before the aboe "cleaning".

Edit: This solution will work in millivolt system (450 mV-open,~220 mV closed). the current in this case is about 0.450 ma. The switch contacts get contaminated under this regiment. Using a jig to have the switch operate under. 125 volts 40 va range will clean the contacts. This is not the wall switch, it is located inside the fire place and its role is to sense if the pilot is lit. For safety remove ths switch from the fireplace when working with 125 volts.

  • OK now you've really lost me :) I'm pretty sure that the wall switch is not the problem. If I bypass it completely (shorting the 2 SW1 leads right at the fireplace) the problem is the same. Or are you referring to a different switch? Where would the mercury switch be in this fireplace? This is a 3V IPI system . . . or am I totally wrong on this ...? Oct 8, 2017 at 2:29
  • The OP bypassed the switch with no change so it is not the problem.
    – Ed Beal
    Oct 10, 2017 at 21:07
  • I guess I'm still trying to figure out what I should be seeing at the valve contacts (volts/amps/ohms) when it should be turning on. If I'm seeing the correct voltage between TP/THTP . . . which I think I am (~480mv) . . . is that what turns the main valve on? Or does TH/THTP need to be activated somehow? If so, how . .. . what am I expecting to see between those contacts, etc.??? Anyone ??? Oct 12, 2017 at 22:13
  • I know nothing about 3V IPI systems. The above solution may not apply.
    – JPR
    Oct 13, 2017 at 14:49

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