Here’s a head scratcher – Question about an LP fired condensing hot air furnace….. What causes LP gas burner flash back? – ie. Burner lights but intermittently retains some flame within the burner. Sometimes the left one, sometimes the right, sometimes both. Gas supply is OK at 14″wc., 11″WC while running, Manifold pressure is OK at 9 to 10″WC matching the rating on the unit (Heil NULK050AF02 2 burner condensing furnace)not a sealed combustion type. Shutter position has no effect on this. Line pressure is unaffected while other appliances run. When burners (2) light properly, 25 degree air temp rise is in spec., firing rate is good. Flame appearance is good. Heat exchanger appears to be OK, unobstructed vent pipe. The Honeywell gas valve on this unit (VR8440P2013) has been replaced already with little improvement. Is this just a lousy valve design? Does anyone make an alternative? Gas valve is a step-opening type , If burner is shut off and immediately re-lit to defeat the step opening, it reliably lights properly. Orfices look new, not monkeyed with. Is there any way of adjusting the initial step pressure up from around 2 or 3″wc? Could this be a draft problem? I’d welcome any ideas !!
Usually the problem is related to two things with LPG one being incorrectly set air ports or slides and the other being the ingress into the piping system of the wax compound commonly found when Propane gas is vaporised and reduced in pressure.
Selgas Services Ltd Craftsman Gasfitters, Plumbers, Electrical Service Technicians