Laars 250 burner won't fire

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Laars 250 burner won't fire

Postby tacobill » Wed 20 May, 2009 22:23

I have a Laars LG 250 and the main burner won't fire... I can get the pilot lit no problem., so i assume that means the piolet generator is fine, and I hate to assume but we all do it all the time.. I'm good with electronics so i can test the equipment if I knew where to go from here...I've bypass the on off swith on the unit for test propose only and still nothing.. also checked continunty on wiring and there ok.. tell me more please.. :wave:

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Laars 250 burner won't fire

Postby Denali » Thu 21 May, 2009 06:03


I assume you have good flow through your system? Low flow will keep the burners off. You can jump the pressure switch to see if the flow is keeping it off.

A common reason here in California that keeps the burners off is spider webs in the gas orifices. Not too difficult to take apart and get them cleaned out.

First make sure one of the safety switches isn't holding it off and then I would check out the gas orifices.

Good luck with it.
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Laars 250 burner won't fire

Postby Me... » Thu 21 May, 2009 09:21

Clean and tighten all the connections. Millivolt heaters are notorious for not firing due to this. You only start with 3/4 (750mv) of a volt and any degradation caused by slight corrosion or loose connections quickly makes that voltage fall too low to open the main gas valve. After the voltage travels through all the wiring, switches and controls it still needs almost 1/2 volt (500mv) left open the main valve and you still need around 1/4 volt (250mv) to maintain that.

That said, go call a gas fitter. I really don't like describing how to work on these because of the potential for someone to cause a great deal of damage to themselves, others or anything nearby. You would not believe the crazy things homeowners will do a heater in order to try and make it work.

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