Hot Dawg 2nd Call For Heat Not Working

Rlhall6310

I am not a heating contractor. Thought this would be an easy fix!

Before I purchase any more parts. Working on my 2001 Hot Dawg. Has run beautifully for years in my garage workshop. Clean environment. Michigan resident so only used during cold weather months.

Issue: If the unit has been turned off completely, and then turned on using the thermostat to set the desired temperature, everything works as it should, things click, gas on, igniter lights, tubes fill with flame, fan goes on and the shop will come to the set temperature and the unit turns off. Just as expected.

However after the temp drops below the thermostat setting and the thermostat is again calling for heat, to maintain the temperature, the unit goes into a series of clicks but the igniter does not light, no flame in the tubes and then the fan starts running with no heat. Running and running until I use the thermostat to turn the unit off.

After a while, if I again turn the unit on to a set temperature, everything works again as it should on the first sequence but fails to light on the second call for heat.

I have replaced the wall thermostat with recommended Honeywell, and purchased a Robert Shaw Replacement Igniter for my model, but still having the same problem. First turned on everything works fine, second call for heat and nothing but the fan running blowing cold air around because there is no flame in the tubes.

Will a OEM Fame Sensor fix this? Could it be the Robert Shaw Igniter?
Thx Bob Hall

HomerJSmith

Sounds like an intermittent heat related issue, maybe the control board or a connection in the circuitry? Unplug any sockets or connections and re connect them. Solder and circuit traces on the board are a common issue.

EdTheHeaterMan

There is a sequence of operation that starts at "turned on using the thermostat" and ends with "shop will come to the set temperature". The clicks and ignition and all the other steps must happen in the correct sequence to get the flame to operate safely. When there is a failure, the experienced technician will know all the steps that it takes to get a successful ignition. Then watch the appliance go thru the steps, and watch for what step is missing. For example: If the ignitor works and there is a flame for a short time, then it extinguishes within a few seconds, the experienced tech would look at the flame sensor and the control that senses the flame. On the other hand if the Ignitor does not glow (or spark, depending the system) and there is no flame at all, then they would look at the ignition system for problems.

So your next step is to look at the system as it fails to light and starts to blow cold air. Look, listen and observe. It is unlikely the fact that the system is trying to start a "second time" is the problem. The ambient temperature of a warm room compared to a cold cold room might be a contributing factor. Look at the I/O manual for the Maintenance section. There are several things that may be easy to do in order to get this problem solved. The first that comes to mind is the flame sensor. Sometimes just cleaning the flame rod with emery cloth will solve this problem.

Mr. ED

HVACNUT

I just looked at a wiring diagram for a Hot Dawg. Not sure if it's the same as a 2001 model, but from what you describe, it seems like the pressure switch isn't opening when the first call for heat ends. On the second call for heat, the gas valve will not open if the control detects a closed pressure switch before a heat demand.
Check the hose of the pressure switch, and the bungs that the hose connects to. Sometimes the holes get clogged. I had one last week on a 20 year old Goodman furnace that another tech diagnosed as a faulty pressure switch, when in fact it was just doing its job. Use a small paper clip or piece of thermostat wire to clear the holes.
Do not enlarge the holes or go deep into the pressure switch. 
Shut off the power first of course.