Just moved into a 40 year old house that has an RUUD model UGPH-07EAMGR furnace. Went to check the filter (which of course was loaded), and it was just sitting over the insertion slot. Suspect someone put the wrong size in (measures 25X16X1). Can someone tell me the proper size filter for this unit. Found the specs for the UGLH version and it says two 12X20, but that seems too small. The slot width measures 15'' across.

SOURCE: Ruud Furnace won't turn on

Take of the access panel on the furnace and look for a wiring diagram either on the back of the panel or inside the housing. There will be a diagnostic chart on it that will give you a hint what 2 flashes mean. I think it is a "no Ignition" code. If it is, with the access panel off and the door switch taped in the closed position, the furnace will try to start if the thermostat is calling. You want to look at the control module to see if it is flashing, then you should notice a small fan that pushes out the combustion products start to turn. Then if you look in a small view port, you should see an orange glow followed by a clicking noise at the gas valve. Then you should notice a blue flame in the view port. This flame must stay on for 5-6 seconds or the unit will turn it self off. If one of these do not happen, you will need a technician to troubleshoot it. Check to see if all wires and hoses are tight and in place. Make sure your condensate hoses are not blocked and free of water. Make sure there is no blockage in your vent pipe(s). 

Let us know what you found. 

SOURCE: RUUD Heater and Ac MODEL #UGPH-07EAUER

It sounds like the thermostat is not functioning correctly. Has it been changed recently? I think the green wire is connected directly with red somewhere, maybe touching within the wiring in the wall. Also make sure the thermostat is set to auto not on. Sorry if you knew that but you would be surprised how many people don't.

SOURCE: Filter Placement Ruud UBHA

hey brad first you need to indentify wich is your supply and wich is the return after you have done that the filter is allways on your retun side however not allways is the filter set up at the air handler sometimes its in a duct sytemn on the ceeiling or wall hope you find it

SOURCE: Small pipe running from outside unit freezing up

SOUNDS LIKE THE FAN SPEED MAY BE TO LOW SO AS THE AIR GOES THROUGH THE COIL IT WILL START TO FREEZE HAVE SOMEONE CHECK THE FAN SPEED MAKE SURE IT IS ON HIGH ALSO MAKE SURE IF THAT IS THE ONLY FILTER ON THE SYSTEM

SOURCE: RUUD UPGH air/furnace just quit....no response...where to begin?

is the power light on the board lit? IF NOT THE 3 AMP OR 5 AMP FUSE COULD HAVE BLOWN ON THE BOARD