Teledyne Laars Mark V type DM heater

[amazed11]

Hi everyone
I recently got my house and we have a Teledyne Laars Mark V type DM pool heater. I did some dig online and found the user manual. I successfully turned the gas valve switch to pilot position and was able to light the pilot tube(I can actually see the fire in front of the tube just like a in house gas heater). But then when I tried to turn the gas switch to ON position, somehow the switch got stuck and just won’t turn. The switch is kind of loose and it comes with a flathead screw in the center of the knob. The knob can be easily taken off with a flathead screwdriver. Does anyone know what could cause this? Should I be replacing the switch knob?

 

[Bperry]

Hi everyone
I recently got my house and we have a Teledyne Laars Mark V type DM pool heater. I did some dig online and found the user manual. I successfully turned the gas valve switch to pilot position and was able to light the pilot tube(I can actually see the fire in front of the tube just like a in house gas heater). But then when I tried to turn the gas switch to ON position, somehow the switch got stuck and just won’t turn. The switch is kind of loose and it comes with a flathead screw in the center of the knob. The knob can be easily taken off with a flathead screwdriver. Does anyone know what could cause this? Should I be replacing the switch knob?

Sometimes you need to press the knob in, in order to turn it.

 

[1poolman1]

Hi everyone
I recently got my house and we have a Teledyne Laars Mark V type DM pool heater. I did some dig online and found the user manual. I successfully turned the gas valve switch to pilot position and was able to light the pilot tube(I can actually see the fire in front of the tube just like a in house gas heater). But then when I tried to turn the gas switch to ON position, somehow the switch got stuck and just won’t turn. The switch is kind of loose and it comes with a flathead screw in the center of the knob. The knob can be easily taken off with a flathead screwdriver. Does anyone know what could cause this? Should I be replacing the switch knob?

When you depressed the knob to light the pilot, did it raise back up when the pilot was lit and you removed your hand/finger? If not, you likely need a new gas valve, somewhat difficult to find for that dinosaur of a heater. A heater with a stuck gas valve is not safe to operate and you never want to "un-stick" a gas valve. You also don't know if the pilot will remain lit or the pilot generator has enough voltage to actually run the heater.

If the original General Control valve is still in the heater, or the Honeywell, it will need to be replaced with a newer valve, likely by Robertshaw. The pilot tubing will need to be replaced along with the valve (most of the time it will come in a kit), and you may lose the "viso-flame" pilot lighting tube. It will need to be a millivolt valve with a rated btu capacity of at least the rating of the heater. You will also probably need a new pilot generator. Just in parts, you are looking at +/- $300.00 to $350.00, maybe more.

Since you are not familiar with working on a large gas appliance, for the sake of safety, it is better to have someone with the expertise of working on an old heater like that do the job. Not many of us around anymore. Its not really a DIY project if you are not somewhat trained. Thirty years ago, Laars had heater schools that spent one full day on those type heaters and the next on electronic ignition heaters. Those schools are long gone, but I still have the manual that went along with the class.

If you really want to heat your pool or spa, the safest way to do it is to get a new heater. That one hasn't been made for over 40 years