Sterling 75,000 tube heater help

[ph1gering]

I recently picked up a 75,000 BTU tube heater used - http://www.h-mac.com/sterling-slr75.html - manual here..

I had to convert it to gas new spring and tapped into the yellow common for 24v power for my wifi thermostat.

Everything was working great for 3-4 weeks, except an occasional failure to light on the first three attempts, it would lock out and usually fire first try after the lock out cleared. I generally could just cut power and try again it would fire.

Now today it wont fire at all, getting three blinks on the control unit, manual says it was a failure to start and locks out.

I am getting Good spark from the Direct spark ignition, I put a gauge on the gas valve it opens when the unit sparks and I am getting 3.5-3.8 WC on my gauge which is exactly what the manual says and the blower unit is cycling fine so its not an air senor issue. I cant figure out why this isn't firing all of a sudden? looking for any advice.

 

[ph1gering]

bueller? bueller? bueller?

Messed around for another 30 minutes today, still can't get the unit to fire. Good spark, gas valve opening, correct pressure, air flow test passed.. Stumped

 

[dfiler2]

Most common problem would be a dirty flame sensor. That is a small rod next to the igniter that sends a signal back to the gas valve telling it the unit has lit. If the valve doesn't get this signal the valve will close. They can be cleaned by using a dollar bill or a light sand paper, just don't be too aggressive. The other thing that can happen is a piece of carbon falls down and can ground out the sensing rod. Be sure there is nothing touching it.

Just in case you don't have a dollar bill a $100 will work fine.

Thought I should add this, sometimes the igniter and the flame sensor are the same rod.

 

[ph1gering]

You are right, flame sensor and igniter are one in this unit, its only a two metal barbs into a spark plug like connector. I got it running, but no clue what it could be, leaning towards a bad igniter.

I took out the igniter again for the 4th time, cleaned it, checked gap to .0125. Then I stuck a torch into the igniter hole and flamed the orifice and air inlets. Put it back together and it fired right up.

I then shut it down took my gauge off and it wouldn't fire again. So did the same thing again and it fired again. I left it on for two hours got the shop up to 60 again, shut it down and cycled it several times it came on each time. But certainly doesn't give me a warm fuzzy feeling of finding a smoking gun.

Do these heaters like to stay well above freezing? I have been keeping the shop at 40 and only kicking it up when I am out there.

 

[dfiler2]

A couple of thoughts, if there is a sparkplug like connector on the end of a ceramic igniter rod make sure that connector is tight. Make sure the igniter is cleaned well with the dollar bill. Also check to be sure you have a good ground and that the polarity on the outlet is not reversed.
Question, when it fails does it go through the valve opening then igniter then flame for 3 seconds then valve closes, or does it just try to ignite and no flame. If you are getting a flame for a few seconds then it is most likely the flame sensor. They are a thermopile and do produce a small amount of electricity and they do sometimes just fail.

 

[ph1gering]

Connection is good and tight, I cleaned it very lightly with a brass brush, I could try with a dollar bill tmrw.

It cycles three times, Valve opens, I can see gas flow 3.5wc, I can see good spark, 3-5seconds later it stops, no flame starts at all, 30 second later it trys it all again, after 3 failures it goes into lock out mode and requires me removing power to reset unit.

Its again not lighting again just tried from my wifi thermostat, its in heat mode, but the room hasn't got any hotter indicating it didn't light again. grr...

 

[dfiler2]

Ok, so if you're not getting a flame then it's probably not getting gas. Have you checked the orifice. You may want to pull it out and make sure there isn't something getting blown into the opening plugging it every once in a while, a small burr can let loose after years of use and cause a problem. You can carefully clean the orifice with a torch cleaning tool.

Gotta love those WIFI thermostats though, my shop is about 3 blocks from my house so It's really nice to warm it up before I get there or turn the heat down after I leave when I forget to.

 

[ph1gering]

I'll drop the unit tmrw and check it out, but its a brand new orifice, i just converted from propane to Gas before installing in my shop so new spring and orifice. Also brand new lines and drip legs etc..

So i guess it could be something got blown into it or rust or something. Thanks for all the tips frustrating... Love my wifi thermostats!

 

[dfiler2]

Is the 3.5-3.8 WC on the outlet side of the gas valve?

 

[ph1gering]

Gas coming into the unit is set by local company to 7.5-14wc, I forget what he told me it was set at. There are two ports on the gas valve, I am checking after the solenoid.

So when the valve is closed it reads zero, then when it opens allowing gas into the system it jumps to 5wc briefly then drops instantly to 3.5ish. I had to put a new spring in when i changed to Gas and had to adjust this till i got to the optimal setting.

 

[dfiler2]

To me everything is pointing to a plugged line or orifice after the valve. You might also want to re-check the hole size in the orifice, the hole for NG should be larger than the one for LP.