Need advice from a heating tech

[midnightventure]

I work for Modine and I bought and installed one of their ceiling hung heaters that was on clearance. Installed it in Sept. and it worked perfect until last week when the weather cooled off drastically. It is hooked up to a 100 lb bottle that probably has a foot of liquid left in it. The pilot went out and I can't get it to light again. I assumed it was a pressure problem. Yesterday it got into the 50s and it worked again. I figured that confirmed what I thought. Today it cooled off again. I made a pressure gauge for inches of water column from plans on the internet. Hooked it up to the input side of the valve ( a Robertshaw 720-402) and it measured exactly 11 inches just like it was supposed to. Part of my problem is that the company sent instructions for an intermittent pilot valve and mine is a standing pilot. When I hooked the gauge up to the output side it shows no pressure and of course I can't get it to light again. What does an expert think?

[Marcarl]

I think you have some moisture in the line, take it off, thaw it out, blow it through and reinstall it. I'm a meat processor, not a heating mechanic, but that's what I would do first.

[Leland]

You don't say how many BTUs your heater is rated for, but as you can see from the attached chart, the tank's vaporization rate is greatly effected by the outdoor temperature.

[straycatt]

I think you have some moisture in the line, take it off, thaw it out, blow it through and reinstall it. I'm a meat processor, not a heating mechanic, but that's what I would do first.

 

 

Ding, ding, ding.

This is the likely culprit, but it can also be dependent on several other factors......What type of elevation is the unit heater mounted at versus the tank? Do you know what the regulator setting is? What size gas line did you run, A. from the tank to the regulator and B. from the reg to the appliance?? Also is the gas line sized properly for the BTU load and how far is the run?

 

As a professional Plumbing/Mechanical Inspector I look at it from an overall installation standpoint. If it did freeze, why? If it is a pressure problem, what? So I ask a lot of questions.

[midnightventure]

The line is only about 5' from the tank to the heater. I have the 11 wc that I'm supposed to have at the control valve on the heater. Tommorow I am going to take out the pilot line and blow out the orifice.

[straycatt]

Hmmmm, could also be a defective gas valve on the unit itself. Do not blow compressed air thru the gas valve itself. (you probably know that, but it must be said) The springs and diaphragm inside the valve don't respond well to high pressures. Anything more than about 1/2 pound will damage it.

Do what you will with the pilot tube and orifice.

 

The more that I think about it, it's got to be an defective or iced gas valve. You've got LP to the gas valve but not thru the gas valve. Gotta be the gas valve.

[uncledj]

Just for the record, I am a heating tech. (24 yrs)

I wouldn't worry so much about the propane supply as a problem as I would a failing (weak) thermocouple or possibly a restricted pilot orifice. Spiders and wasps love to build nests in the most inconvenient places, often causing problems, most especially in equipment that isn't used in the warmer months.

Make sure that you have a strong pilot flame, and that it contacts the thermocouple. It should heat the thermocouple to the point that it glows cherry red.

After checking these things, if you still have a problem, feel free to call me at 614 595 2046, and we'll see if we can figure it out together.

Hope this helps.

John

[FROG MAN]

I made a pressure gauge for inches of water column from plans on the internet

I'm interested in seeing those plans been needing one of my own.I would start with cleaning the pilot orfice and replacement of thermocouple is a low dollar item.

[midnightventure]

Here is basically what I built although I made mine neater and carefully marked the lines on my board ahead. Then you have to be real careful to get your waterline at zero.

http://www.komar.org/faq/manometer/

[midnightventure]

Thanks for the replies. I got it going this morning. It was 16 degrees outside. Blew out the pilot orifice. Got the pilot to light and turned the thermostat up and it took off. Then I checked the out put pressure and it was 7 WI and supposed to be 10. Used the internal regulator to adjust that. It's burning good and I believe putting out more heat than it did before. I think that I had a hard time believing that it could be plugged when it had only been installed for 2 months. Maybe a spider was working in the box all summer while I was waiting for the attic to cool off enough to work in.